Evolutionary based multi-criteria optimization of an integrated energy system with SOFC, gas turbine, and hydrogen production via electrolysis Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-14 Ehsan Gholamian, Pedram Hanafizadeh, Ali Habibollahzade, Pouria Ahmadi
The aim of this study is to exploit the waste heat of a biomass-based solid oxide fuel cell (SOFC)–model (a)–in a gas turbine (GT) to enhance the power generation/exergy efficiency (model (b)). Moreover, surplus power which is generated by the GT is transferred to a proton exchange membrane electrolyzer (PEME) for hydrogen production (model (c)). Parametric study is performed to investigate the influence of the effective parameters on performance and economic indicators. Eventually, considering exergy efficiency and total product cost as the objective functions, the proposed models are optimized by multi-objective optimization method based on genetic algorithm. Accordingly, the optimum solution points are gathered as Pareto frontiers and subsequently favorable solution points are ascertained from exergy/economic standpoints. Results of parametric study indicate that model (b) is the best model as it has higher exergy efficiency and lower total product cost. Moreover, model (c) may be a more suitable model compared to the model (a) because of higher exergy efficiency and capability of hydrogen production. The results further show that, at the best final solution point, the exergy efficiency and total product cost of the model (b) would be 33.22% and 19.01 $/GJ, respectively. Corresponding values of exergy efficiency and total product cost of the model (c) are 32.3% and 20.1 $/GJ. Moreover, the rate of hydrogen production of the model (c) is 8.393 kg/day, at the best solution point. Overall, the integration methods are promising techniques for increasing exergy efficiency, reducing total product cost and also for hydrogen production.
Hydrogen storage in Zr0.9Ti0.1(Ni0.5Cr0.5-xVx)2 Laves phase, with x = 0, 0.125, 0.25, 0.375, 0.5. A theoretical approach Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-14 A. Robina, P. Bechthold, A. Juan, C. Pistonesi, M.E. Pronsato
Density functional calculations were performed on Zr0.9Ti0.1(Ni0.5Cr0.5-xVx)2 Laves Phase, with x = 0, 0.125, 0.25, 0.375 and 0.5, in order to study its H absorption capacity. Binding energy, electronic structure and bonding were analyzed for the intermetallic compound with different V content and increasing amounts of hydrogen.The optimized geometry was found in good agreement with experimental data of the C14 Laves phase. Hydrogen locates preferentially in A2B2 tetrahedral sites in the AB2 matrix (A = Zr, Ti; B = Ni, Cr, V) but AB3 and B4sites are also stable. The volume of the intermetallic and the H binding energy increases with vanadium content. Theoretically H absorption is possible up to 4.5 H/F.U. but the strongest binding energy is achieved with 3 H/F. U.The main contribution to density of states is due to d states of all components of the structure and an H-metal bonding is observed in the range −10 to −4 eV.
Long-term effect of carbon nanotubes on electrochemical properties and microbial community of electrochemically active biofilms in microbial fuel cells Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-14 Yaping Zhang, Xi Chen, Yong Yuan, Xingwen Lu, Zuoyi Yang, Yujie Wang, Jian Sun
Carbon nanotubes (CNTs) have been widely exploited to improve anodic performance, but information is needed on their long-term stability for improvement. Herein, we prepared a novel CNTs-modified graphite felt (CNTs-GF) by a simple and scalable process and evaluated its long-term performance using anaerobic sludge as inoculum. the MFC with CNTs-GF yielded a sustained enhancement of power output, increasing from 1.93 ± 0.09 W m−2 after 1 month to 2.10 ± 0.05 W m−2 after 3 months and reaching 2.00 ± 0.10 W m−2 after 13 month, indicating the enhancement in electricity generation by the CNTs was not declined over one year. However, the bare GF showed a declining tendency of performance during 13 months. The long-term enhancement can be explained by the facts that the CNTs-GF was beneficial to electrochemically active biofilms (EABs) growth and interacted better with EABs and increased the extracellular electron transfer. Community analysis showed an increase in Geobacter in response to CNTs modification. These results demonstrated that CNTs modification could sustain a superior long-term enhancement in MFC performance.
Thermodynamic efficiency analysis of zinc oxide based solar driven thermochemical H2O splitting cycle: Effect of partial pressure of O2, thermal reduction and H2O splitting temperatures Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-14 Rahul R. Bhosale
In this paper, the thermodynamic efficiency analysis of ZnO-based solar-driven thermochemical H2O splitting cycle is performed and compared with the SnO2-based H2O splitting cycle. The HSC Chemistry 7.1 software is used for this analysis and effects of thermal reduction (TH) and water splitting temperature (TL) on various thermodynamic parameters associated with the ZnO-based H2O splitting cycle are explored. The thermodynamic equilibrium compositions allied with the ZnO reduction and re-oxidation of Zn via H2O splitting reaction are identified by varying the TH, TL, and PO2 in the inert gas. The efficiency analysis indicates that the highest cycle and solar-to-fuel energy conversion efficiency equal to 41.1 and 49.5% can be achieved at TH = 1340 K and TL = 650 K. Both efficiencies can be increased further by more than 10% via employing heat recuperation (50%). Based on the cycle and solar-to-fuel energy conversion efficiency values, the ZnO-based H2O splitting cycle seems to be more attractive than SnO2-based H2O splitting cycle.
Evaluation of PrNi0.4Fe0.6O3-δ as a symmetrical SOFC electrode material Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-14 Haoliang Tao, Jianjun Xie, Yefan Wu, Shaorong Wang
Symmetrical Solid Oxide Fuel Cell has identical electrode material on both electrodes, of which the most outstanding advantage is the ability to remove the deposited carbon and other deposits from anode. Owing to the working conditions of electrodes, there are more requirements for electrode materials than normal ones. In this study, we evaluate the traditional cathode material PrNi0.4Fe0.6O3-δ as a symmetrical solid oxide fuel cell electrode material. Unstable as most traditional cathode materials are in fuel gas, however, the result here exhibits PrNi0.4Fe0.6O3-δ has good performance. The peak power density of the cell with PrNi0.4Fe0.6O3-δ electrode in wet methane at 800 °C is 663 mWcm−2 with observable decomposition on anode. After switching the fuel gas on anode to air, the structure recovers quickly. In terms of the recyclable performance, PrNi0.4Fe0.6O3-δ seems suitable for symmetrical solid oxide fuel cell.
Chemical bath deposition synthesis of TiO2/Cu2O core/shell nanowire arrays with enhanced photoelectrochemical water splitting for H2 evolution and photostability Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-14 Lizhen Yao, Wenzhong Wang, Lijuan Wang, Yujie Liang, Junli Fu, Honglong Shi
In this study, we have developed a facile chemical bath deposition (CBD) method to grow p-type Cu2O nanoparticles on n-type TiO2 nanowire arrays (TiO2 NWAs) to fabricate TiO2/Cu2O core/shell heterojunction nanowire arrays (TiO2/Cu2O core/shell NWAs). When used as photoelectrode, the fabricated TiO2/Cu2O core/shell NWAs show improved photoelectrochemical (PEC) water splitting activity to pure TiO2 NWAs. The effects of the CBD cycle times on the PEC activities have been studied. The TiO2/Cu2O core/shell heterojunction nanowire array photoelectrode prepared by cycling 5 times in the CBD process achieves the highest photocurrent of 2.5 mA cm−2, which is 2.5 times higher than that of pure TiO2 NWAs. In addition, the H2 generation rate of this photoelectrode reaches to 32 μmol h−1 cm−2, 1.7 times higher than that of pure TiO2 NWAs. Furthermore, the TiO2/Cu2O core/shell heterojunction nanowire array photoelectrode shows excellent photostability and achieves a stable photocurrent of over 2.3 mA cm−2 during long light illumination time of 5 h. The enhanced photocatalytic activity of TiO2/Cu2O core/shell heterojunction nanowire array photoelectrode is attributed to the synergistic actions of TiO2 and Cu2O for improving visible light harvesting, and efficient transfer and separation of photogenerated electrons and holes.
Laminar burning velocities and flame instabilities of diluted H2/CO/air mixtures under different hydrogen fractions Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-14 Hong-Meng Li, Guo-Xiu Li, Yan-Huan Jiang
An experimental study was conducted using outwardly propagating flame to evaluate the laminar burning velocity and flame intrinsic instability of diluted H2/CO/air mixtures. The laminar burning velocity of H2/CO/air mixtures diluted with CO2 and N2 was measured at lean equivalence ratios with different dilution fractions and hydrogen fractions at 0.1 MPa; two fitting formulas are proposed to express the laminar burning velocity in our experimental scope. The flame instability was evaluated for diluted H2/CO/air mixtures under different hydrogen fractions at 0.3 MPa and room temperature. As the H2 fraction in H2/CO mixtures was more than 50%, the flame became more unstable with the decrease in equivalence ratio; however, the flame became more stable with the decrease in equivalence ratio when the hydrogen fraction was low. The flame instability of 70%H2/30%CO premixed flames hardly changed with increasing dilution fraction. However, the flames became more stable with increasing dilution fraction for 30%H2/70%CO premixed flames. The variation in cellular instability was analyzed, and the effects of hydrogen fraction, equivalence ratio, and dilution fraction on diffusive-thermal and hydrodynamic instabilities were discussed.
Catalytic properties of Sr1−xCexWO4: The role of mixed conduction in methane oxidation Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-12 Rafael Hernandez Damascena dos Passos, Carlson Pereira de Souza, Christine Leroux, Madjid Arab
The catalytic efficiency of ternary strontium cerium tungstate Sr0.5Ce0.35WO4, for the production of syngas through methane oxidation, was investigated and compared to those of binary strontium tungstate SrWO4. Total and partial oxidation reactions were observed for both samples in the temperature range 600–750 °C under CH4/dry air flux. At high CH4 concentration and low temperature with the ternary tungstate as catalyst, the partial oxidation, leading to CO/H2, prevails. This indicates the potentiality of the new strontium cerium tungstate scheelite compound for the catalysis of CH4. Sr0.5Ce0.35WO4 and SrWO4 exhibit different conduction mechanisms. Conduction in the binary compound is related to the overlapping large polaron tunneling model, whereas conduction in the ternary one is due to a correlated barrier hopping phenomenon. The activation energies, in the low temperature range where the partial oxidation occurs, are significantly lower for the ternary compound than for the binary one. These electrical tendencies favor both partial and total oxidation of methane. The correlated barrier hopping conduction in the ternary compound leads to a better partial oxidation rate than conduction through large polaron tunneling.
Perovskite-based proton conducting membranes for hydrogen separation: A review Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-13 Siti Salwa Hashim, Mahendra Rao Somalu, Kee Shyuan Loh, Shaomin Liu, Wei Zhou, Jaka Sunarso
Hydrogen is considered a fuel of the future due to its diversified supply and zero greenhouse gas emission. The application of advanced membrane technology for hydrogen separation within the larger hydrogen production process context can substitute the use of more expensive and energy intensive cryogenic distillation and pressure swing adsorption technologies. This review overviews the basic aspects and progresses in perovskite-based proton conducting hydrogen separation membranes. Different configurations such as symmetric, asymmetric, hollow fiber, and surface modified perovskite membranes with various compositions are discussed and summarized. The challenges and future directions of such membranes are also elaborated.
Favourable band edge alignment and increased visible light absorption in β-MoO3/α-MoO3 oxide heterojunction for enhanced photoelectrochemical performance Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-13 Nisha Kodan, Aadesh P. Singh, Matthias Vandichel, Björn Wickman, B.R. Mehta
Optimum band gap values, favourable band edge positions and stability in the electrolyte are critical parameters required for a semiconductor to have efficient photoelectrode properties. The present investigation carried out on the phase pure α & β MoO3 thin film shows that the low bandgap β-MoO3 possesses a mis-alignment with the water oxidation potential, while a more suitable band alignment is observed for the comparatively large bandgap α-MoO3. Both experimental and DFT calculations show that the valence edge of the orthorhombic (α-MoO3) phase is located at a higher energy (0.9 eV higher in VB-XPS and 1 eV higher in the DOS plots) than the monoclinic (β-MoO3) phase, while the conduction edge value is roughly at the same energy level (−2.5 eV) in both polymorphs. Based on the above investigations, an all oxide heterojunction comprising of β-MoO3/α-MoO3 is found to be suitable for improved PEC performance due to favourable energy band diagram and increased visible light absorption in β-MoO3. Significantly higher cathodic photocurrent is observed for the β-MoO3/α-MoO3 (1.6 mA/cm2 at applied bias of −0.3VRHE under simulated 1 sun irradiation) as compared to the very low anodic response in β-MoO3 (∼1.0 nA/cm2) and α-MoO3 (32 μA/cm2).
Metallic iron doped vitamin B12/C as efficient nonprecious metal catalysts for oxygen reduction reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-13 Sa Liu, Zheng Yang, Liwen Liu, Mengli Li, Yan Wang, Wenjie Lv, Xiaowen Chen, Xinsheng Zhao, Ping Zhu, Guoxiang Wang
The development of efficient nonprecious metal catalysts for oxygen reduction reaction (ORR) is crucial but challenging. Herein, one simple and effective strategy is developed to synthesize bimetallic nitrogen-doped carbon catalysts by pyrolyzing Fe-doped Vitamin B12 (VB12) supported carbon black (Fe-VB12/C). A typical Fe20-VB12/C catalyst with a nominal iron content of 20 wt% pyrolyzed at 700 °C exhibits remarkably ORR activity in alkaline medium (half-wave potential of 0.88 V, 10 mV positive than that of commercial Pt/C), high selectivity (electron transfer number > 3.93), excellent stability (only 6 mV negative shift of half-wave potential after 5000 potential cycles) and good methanol-tolerance. The superior ORR activity of the composite is mainly attributed to the improved mesoporous structure and co-existence of abundant Fe-Nx and Co-Nx active sites. Meanwhile, the metallic Fe are necessary for the improved ORR activity by means of the interaction of metallic Fe with neighboring active sites.
Optimization of MnO2-Graphene/polythioaniline (MnO2-G/PTA) hybrid nanocomposite for the application of biofuel cell bioanode Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-13 Ruma Perveen, Abu Nasar, Inamuddin, Abdullah M. Asiri, A.K. Mishra
This study reports the synthesis of a nanocomposite comprised of graphene (G) supported manganese dioxide (MnO2) incorporated into the network of polythioaniline (MnO2-G/PTA). The hybrid composite was applied as an electrode material for the development of a bioanode. The bioanode was fabricated by the electrochemical entrapment of ferritin (Frt) as mediator and glucose oxidase (GOx) enzyme in the matrix of the as-synthesized MnO2-G/PTA deposited on glassy carbon electrode (GCE) surface. The structural features and electrochemical behaviour of the modified electrodes were investigated by Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The results unfolded that the hybrid electroactive support (MnO2-G/PTA) employed for the immobilization of the enzyme (GOx) established an appropriate electrical cabling between the redox enzyme (GOx) and the electrode surface with the assistance provided by the biocompatible mediator (Frt) working to enhance the electrical signals. The developed GCE/MnO2-G/PTA/Frt/GOx bioanode attained a maximum current density of 3.68 mAcm−2 at 35 mM glucose concentration at a scan rate of 100 mVs−1. Thus, the MnO2-G/PTA/Frt/GOx modified electrode possesses high potential and good biocompatibility for bio-electricity production from glucose.
In-situ ammonia-modulated silver oxide as efficient oxygen evolution catalyst in neutral organic carboxylate buffer Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-10 Dandan Li, Congcong Wei, Qiang Wang, Lin Liu, Dazhong Zhong, Genyan Hao, Jinping Li, Qiang Zhao
Silver-based catalysts with an adjustable structure are promising as efficient oxygen evolution catalysts. Four types of silver-oxide (AgO) morphologies were obtained by potentiostatic deposition in situ in organic carboxylate by altering the amount of ammonia as the complexing agent. AgO films can be used in the oxygen-evolution reaction; AgO that is formed by using potassium acetate that contains 1.32 mM ammonia as an electrolyte exhibits preferable performance. Catalyzed water oxidation occurs in 0.1 mol/L potassium phosphate solution (pH 12.3) with an average activity of 3.5 mA/cm2, and persists for at least 10 h at 2.03 V (vs. Reversible Hydrogen Electrode, RHE). Overpotential is 438 mV at a current density of 1 mA/cm2. The Faradaic efficiency is 94.4%. Samples were well characterized by X-ray powder diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy.
Methane bi-reforming over boron-doped Ni/SBA-15 catalyst: Longevity evaluation Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Tan Ji Siang, Long Giang Bach, Sharanjit Singh, Quang Duc Truong, Van Thi Thanh Ho, Nguyen Huu Huy Phuc, Feraih Alenazey, Dai-Viet N. Vo
A highly active and stable boron-promoted catalyst was successfully prepared by using the sequential incipient wetness impregnation technique and examined for methane bi-reforming reaction. The initial investigation found that the NiO and B2O3 particles were dispersed on the outer surface of the high surface area SBA-15 support. In addition, the catalytic activity was increased linearly with the tested reaction temperature due to the endothermic nature of the reaction. In fact, the catalyst achieved the CH4 conversion and H2/CO molar ratio of approximately 67.3% and 2.7, respectively at 1073 K. The resulting product ratio is highly suitable for downstream Fischer-Tropsch (FT) synthesis. The B-promoted catalyst showed the lowest degree of catalyst deactivation (4%) at 1023 K. Additionally, the XPS measurements unveiled that the boron facilitates the adsorption of CO2 by donating electrons to the neighbouring Ni cluster and thus improved its catalytic performance. Furthermore, Raman and XRD analysis revealed that the boron promotion on 10%Ni/SBA-15 could prevent the reoxidation and deposition of carbonaceous species.
Kinetics of iron ore pellets reduced by H2N2 under non-isothermal condition Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Minghua Bai, Hu Long, Liejun Li, Dong Liu, Su-Bo Ren, Chang-Fu Zhao, Jiayuan Cheng
Direct reduction experiments under non-isothermal conditions are induced to simulate reaction in the actual hydrogen shaft furnace. Morphology of metalized pellets is analyzed through optical microscope. Weight loss during reduction is recorded and the model of un-reacted core is adopted for dynamic analysis in sections. Compressive strengths of products are also detected. Results show that reduction rates under heating conditions are lower compared with the isothermal situation. The un-reacted core still exists in products. It is found through kinetics analysis that the reaction is firstly mix controlled by the interfacial chemical reaction and internal diffusion, and then controlled dominantly by the interfacial chemical reaction as the temperature and efficient reduction gas content increase gradually with reaction going on. The compressive strengths under heating condition are also lower than the value obtained at constant temperature of 900 °C.This phenomenon may be caused by the crystalline transformation and volume expansion during the dominating Fe2O3 to Fe3O4 reduction at lower temperature. This study can provide scientific guide for rational utilization of hydrogen energy in iron making.
Theoretical study of hydrogen production by ethanol steam reforming: Technical evaluation and performance analysis of catalytic membrane reactor Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Majid Saidi, Alireza Jahangiri
Ethanol steam reforming over a Co/Al2O3 catalyst was studied theoretically in a catalytic PdAg membrane reactor (CMR). A mathematical model has been developed to elucidate the behavior of CMR by taking into account the chemical reactions, heat and mass transfer phenomena. The effect of operating parameters on the performance of CMR has been evaluated in terms of ethanol conversion, hydrogen recovery and hydrogen yield. The results revealed the high performance of this configuration is related to the continuous removal of hydrogen from the retentate side, shifting the reaction equilibrium towards hydrogen formation. Sensitivity analysis of operating parameters indicate that ethanol conversion is favored at higher temperatures, pressures, sweep ratios and feed molar ratios. Moreover, increasing the feed molar ratio enhances the ethanol conversion, and decreases the hydrogen recovery due to reduction of partial pressure of hydrogen and consequently decreasing the driving force for the hydrogen permeation through the membrane.
Hydrogen production via CO2 dry reforming of glycerol over ReNi/CaO catalysts Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Nur Nabillah Mohd Arif, Sumaiya Zainal Abidin, Osarieme Uyi Osazuwa, Dai-Viet N. Vo, Mohammad Tazli Azizan, Yun Hin Taufiq-Yap
The present work investigates the performance of Re-promoted Nickel-based catalyst supported on calcium oxide for glycerol dry reforming reaction. The catalysts were prepared using wet impregnation method and their catalytic performance was tested in a packed bed reactor with CO2 to glycerol ratio (CGR) of 1–5, reaction temperature of 600–900 °C and gas hourly specific velocity (GHSV) of 1.44 × 104–7.20 × 104 ml gcat−1 s−1. The optimum operating temperature for both Ni/CaO and ReNi/CaO is 800 °C, with the GHSV of 3.6 × 104 mL gcat−1s−1. The optimum CGR for Ni/CaO and ReNi/CaO is 1.0 and 3.0, respectively. At this condition, hydrogen gas is directly produced from glycerol decomposition and indirectly from water-gas-shift reaction. After 2 h at the optimum conditions, 5% ReNi/CaO gives optimal glycerol conversion and hydrogen yield of approximately 61% and 56%, respectively, while in comparison to 15% Ni/CaO, the conversion and yield are 35 and 30%, respectively. Characterization of the spent catalysts showed the existence of whisker carbon from the CO2 hydrogenation and methanation processes. By comparing to 15% Ni/CaO, the addition of Re increases the acidic sites of the catalyst and enhanced the surface adsorption of OH group of the glycerol. The adsorbed glycerol on the catalyst surface would further react with the adsorbed CO2 to yield gases products. Thus, the catalytic activity improved significantly.
Thermal management optimization of an air-cooled hydrogen fuel cell system in an extreme environmental condition Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Xin Gao, Anders Christian Olesen, Søren Knudsen Kær
An air-cooled proton exchange membrane (PEM) fuel cell system is designed and under manufacture for telecommunication back-up power. To enhance its competence in various environments, the system thermal feature is optimized in this work via simulation based on a computational fluid dynamics (CFD) model. The model is three-dimensional (3D) and built in the commercial CFD package Fluent (ANSYS Inc.). It makes the full-scale system-level study feasible by only considering the system essences with adequate accuracy. Through the model, the optimization is attained in several aspects. Firstly, structural sources of a notable thermal disparity under an extremely low environmental temperature (−40 °C) are identified. Secondly, system design modifications are explored including elimination of interruptions in the airflow, implementation of fins, relocation of the system fan, etc. At last, an operation setting, the intake airflow magnitude, is also studied for a more uniform airflow and in turn a suppressed temperature disparity inside the system. Following the guidelines drawn by this work on the system design and the operation setting, the air-cooled fuel cell system can be expected with better performances and a longer lifetime. In addition, this work demonstrates the effectiveness of a compact 3D CFD model in improving a fuel cell system design and operation.
Preparation of highly dispersed Cu/SiO2 doped with CeO2 and its application for high temperature water gas shift reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Liuye Mo, Eng-Toon Saw, Yasotha Kathiraser, Ming Li Ang, Sibudjing Kawi
Highly dispersed Cu/SiO2 catalysts doped with CeO2 have been successfully prepared via in-situ self-assembled core-shell precursor route. The prepared catalysts were characterized by XRD, SEM, TPR, chemisorption and XPS techniques. The results showed that our newly developed method could not only prepare highly dispersed supported metal catalysts but also highly dispersed supported CeO2 on silica. The highly dispersed CeO2 showed strong interaction with highly dispersed Cu. The synergy between the highly dispersed CeO2 and the highly dispersed Cu exhibited high catalytic activity for high temperature water gas shift reaction compared to the catalysts prepared with the routine method of incipient impregnation.
Optimal operation of a photovoltaic generation-powered hydrogen production system at a hydrogen refueling station Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Hirohisa Aki, Ichiro Sugimoto, Tokuyoshi Sugai, Masahisa Toda, Masahiro Kobayashi, Masayoshi Ishida
As the popularity of fuel cell vehicles continues to rise in the global market, production and supply of low-carbon hydrogen are important to mitigate CO2 emissions. We propose a design for a hydrogen refueling station with a proton exchange membrane electrolyzer (PEM-EL)-based electrolysis system (EL-System) and photovoltaic generation (PV) to supply low-carbon hydrogen. Hydrogen is produced by the EL-System using electricity from PV and the power grid. The system was formulated as a mixed integer linear programming (MILP) model to allow analysis of optimal operational strategies. Case studies with different objective functions, CO2 emission targets, and capacity utilization of the EL-System were evaluated. Efficiency characteristics of the EL-System were obtained through measurements. The optimized operational strategies were evaluated with reference to three evaluation indices: CO2 emissions, capacity utilization, and operational cost of the system. The results were as follows: 1) Regardless of the objective function, the EL-System generally operated in highest efficiency state, and optimal operation depended on the efficiency characteristics of the EL-System; 2) mitigation of CO2 emissions and increase in capacity utilization of the EL-System required trade-offs; and 3) increased capacity utilization of the EL-System showed two opposing effects on hydrogen retail price.
Techno-economic comparison of anode-supported, cathode-supported, and electrolyte-supported SOFCs Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Milad Ebadi Chelmehsara, Javad Mahmoudimehr
Different types of self-supported SOFCs (i.e., anode-supported, cathode-supported and electrolyte-supported SOFCs) have been compared in literature mostly from technical point of view. In this study, the mentioned types of SOFCs are compared from technical and economic points of view simultaneously. In this regard, “maximum power density” and “material cost of PEN layer” are taken as objective functions. These functions are evaluated through numerical modeling and based on available cost data, respectively. The results illustrate that the cathode-supported SOFC is the optimal choice when power density is regarded alone. On the other hand, the electrolyte-supported SOFC is observed to be the optimal option when the material cost of PEN is considered as the only objective function. However, the anode-supported SOFC makes the best trade-off between the two objective functions when they are simultaneously taken into consideration. The results also indicate that the electrolyte-supported SOFC leads to a symmetrical and most uniform current density distribution as compared to the electrode-supported ones in which peak local current densities tend toward non-supporting side. The paper discusses in detail the reasoning for the mentioned observations.
A review of CH4CO2 reforming to synthesis gas over Ni-based catalysts in recent years (2010–2017) Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 Guojie Zhang, Jiwei Liu, Ying Xu, Yinghui Sun
In recent years, global warming issue has been a major environmental concern, so the treatment or utilization of the greenhouse gases CO2 and CH4 have become a matter of urgency. Given this realization, dry reforming of methane (DRM) provides a comprehensive utilization of methane and carbon dioxide, which has been investigated systematically. In CH4CO2 reforming reaction, Ni-based catalysts are widely used and promisingly industrialized due to their outstanding features and low price compared with precious metals. In this paper, we emphasize the recent accomplishments in catalyst design for DRM reaction, particularly focusing on the influence of supports, promoters, and preparation methods on the DRM reaction with nickel-based catalysts. We also present a review on the catalytic mechanistic and kinetics of the DRM reaction. Furthermore, this review looks ahead the major challenges and opportunities of nickel-based catalysts in DRM reaction research.
Impact of PTFE distribution across the GDL on the water droplet removal from a PEM fuel cell electrode containing binder Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-11 A.H. Kakaee, G.R. Molaeimanesh, M.H. Elyasi Garmaroudi
By progress of the new generation of electrical powertrains and reducing of the fossil fuel resources, vehicle industry becomes more interested in utilizing proton exchange membrane (PEM) fuel cells. However, practical utilization of them is faced with some challenges including liquid water accumulation in the porous electrodes. The common belief for mitigating this issue is the treatment of electrodes' gas diffusion layers (such as carbon papers consisting of carbon fibers and binder for binding fibers) with a highly hydrophobic material such as poly-tetra-fluoro-ethylene (PTFE). In the current investigation, 3D stochastic reconstructions and 3D lattice Boltzmann simulations are employed to discover the impact of PTFE distribution as well as the role of binder content on the removal process of a water droplet from a PEM fuel cell electrode for the first time. Nine different simulations with three dissimilar PTFE distributions and three dissimilar binder contents are implemented. The results demonstrate that the PTFE distribution and the existence of binder can greatly affect the removal efficiency of water droplet from gas diffusion layer. Unexpectedly, for higher binder contents, the uniform distribution of PTFE is less effective. Besides, for a specific PTFE distribution adding binder can effectively hinder the removal process of droplet.
Controlling the degree of sulfonation and its impact on hybrid cross-linked network based polyphosphazene grafted butylphenoxy as proton exchange membrane Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-12 Amina Ouadah, Tianwei Luo, Shuitao Gao, Changjin Zhu
A new hybrid based polyphosphazene backbone is synthesized via a series of reactions (ring opening of polyphosphazene, bromination, grafting groups, Atom transfer radical polymerization (ATRP) and sulfonation) with a controlled degree of sulfonation. The synthesis is proved via the 1H NMR analysis at different steps. The corresponding membranes were elaborated via a casting method and characterized by 1H NMR, FTIR, and XPS. Conductivity of the synthesized proton exchange membranes is as good as that of the commercial Nafion and displays at the same time a low swelling ratio and water uptake due to the cross-linking process. The membrane's activation energies are very low confirming the easy transport through the channels. As matter of fact, the morphology study reveals a well hydrophilic/hydrophobic nanophase separation. The present membranes are chemically and thermally very stable, no significant weight loss was observed after the Fenton's reagent test and no thermal degradation occurs at temperatures lower than 250 °C (considered high temperature for nowadays proton exchange membranes).
Mesoporous NiO with different morphology: Synthesis, characterization and their evaluation for oxygen evolution reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-12 J. Praveen Kumar, Sachin D. Giri, A. Sarkar
Mesoporous NiO samples with different morphology were synthesized by hydrothermal method, and they were studied as electrocatalysts for oxygen evolution reaction in alkaline solution. The NiO samples were characterized by X-ray diffraction, transmission electron microscopy, N2-adsorption, scanning electron microscopy and X-ray photoelectron spectroscopy. The critical synthesis parameters like hydrothermal reaction temperature, time and molar ratio of precursors were varied using Taguchi experimental method to investigate their effect on morphology and specific surface area of mesoporous NiO samples. The characterization data illustrated the formation of nanoplates, nanorods, and nanoparticles. All the NiO samples exhibited mesoporosity and the specific surface area values in the range of 88–156 m2/g. One of the synthesized mesoporous NiO samples, largely constituting of nanoplates and nanorods with high porosity, exhibited a Tafel slope of 62 mV/dec and achieved a current density of 41.6 mA/cm2 at 1.6 V (vs. RHE). It showed better electrocatalytic activity for oxygen evolution reaction than remaining samples.
Mutual effect of extrinsic defects and electronic carbon traps of M-TiO2 (M = V, Co, Ni) nanorod arrays on photoexcited charge extraction of CdS for superior photoelectrochemical activity of hydrogen production Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-12 Asad Mumtaz, Norani Muti Mohamed, Muhammad Imran Irshad, Asfand Yar, Mohamed Shuaib Mohamed Saheed
Understanding the photoexcited charge carrier dynamics such as separation, transportation and extraction in smart hybrid nanocomposites is the key to high performance solar cells. Nanocomposites possess advantage of broader solar absorption with their fast photoexcited charge separation and transportation but their use as photocorrosion-stable material is yet to be explored. Also, bulk and surface defects in individual components of the nanocomposites boost the efficiency of the solar cells, despite of the fact the recombination of the photoexcited charges at the interfaces lead to a substantial loss of charges and realizing a big challenge. Herein, the extrinsic defects like bulk and surface defects are induced by transition metal (M = V, Co, Ni) doping of M − TiO2 nanorod arrays. Consequently, the hydrothermal synthesis method offers the tuning of the carbon trapping states depending upon the type of the metal doped in M − TiO2 that decelerates the charge carrier dynamics in the M-TiO2/CdS (M = V, Co, Ni) nanocomposites with the increase in the amount of carbon. Excellent charge extraction is observed in VTiO2 (4% carbon) from its CdS sensitizer with photocurrent density of 2.06 mA/cm2 than NiTiO2 (14.6% carbon), TiO2 (18.94% carbon) and CoTiO2 (39.2% carbon) with photocurrent densities of 1.83, 1.46 and 1.34 mA/cm2 at 0 V versus Ag/AgCl under 100 mW/cm2 light intensity, respectively. This shows primary dependence of photoexcited charge dynamics upon the density of the carbon trapping states to be least while secondary dependence upon the density of the extrinsic defects in M − TiO2 to be maximum. This work creates a paradigm for future studies to have a broader insight of the photocatalyst's overall functioning to boost the efficiencies in solar cells by controlling the amount of electronic carbon traps during the synthesis of a large class of inorganic semiconductor photocatalysts.
Assessment of layered La2-x(Sr,Ba)xCuO4-δ oxides as potential cathode materials for SOFCs Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-12 Anna Niemczyk, Anna Olszewska, Zhihong Du, Zijia Zhang, Konrad Świerczek, Hailei Zhao
In this paper, selected layered cuprates with La2-x(Sr,Ba)xCuO4-δ formula are evaluated as candidate cathode materials for Solid Oxide Fuel Cells. Two synthesis routes, a typical solid state reaction and a sol-gel method yield well-crystallized La1.5Sr0.5CuO4-δ, La1.6Ba0.4CuO4-δ and La1.5Sr0.3Ba0.2CuO4-δ materials having tetragonal I4/mmm space group, but differing in morphology of the powder. Fine powders obtained using sol-gel route seem to be more suitable for preparation of the porous cathode layers having good adhesion on the solid electrolyte, but powders obtained after the solid state route can be also successfully utilized. Investigations of structural and transport properties, the oxygen nonstoichiometry and its change with temperature, thermal expansion, as well as chemical and thermal stability are systematically performed, to evaluate and compare basic physicochemical properties of the oxides. At room temperature the average valence state of copper is found to be in 2.2–2.35 range, indicating oxygen deficiency in all of the compounds, which further increases with temperature. The conducted high-temperature X-ray diffraction tests reveal moderate, but anisotropic thermal expansion of La2-x(Sr,Ba)xCuO4-δ, with higher expansion at temperatures above 400 °C occurring along a-axis, due to the oxygen release. However, the corresponding chemical expansion effect is small and the materials possess moderate thermal expansion in the whole studied temperature range. All compounds show relatively high electrical conductivity at the elevated temperatures, related to the Cu2+/Cu3+ charge transfer, with the highest values recorded for La1.5Sr0.5CuO4-δ. Comprehensive studies of chemical stability of the selected La1.5Sr0.5CuO4-δ material with La0.8Sr0.2Ga0.8Mg0.2O3-δ solid electrolyte revealed complex behavior, with stability being dependent apart from temperature, also on morphology of the powders. A model describing such behavior is presented. While it is possible to minimize reactivity and characterize electrochemical properties of the La1.5Sr0.5CuO4-δ-based cathode layer, usage of the buffer layer is indispensable to maintain full stability. It is shown that mutual chemical compatibility of La1.5Sr0.5CuO4-δ and commonly used La0.4Ce0.6O2-δ buffer layer material is excellent, with no reactivity even at 1000 °C for prolonged time. Laboratory-scale fuel cell with the La1.5Sr0.5CuO4-δ cathode sintered at the optimized temperature is able to deliver 0.16 W cm−2 at 800 °C while fueled with wet hydrogen.
Chemical degradation of PFSA ionomer binder in PEMFC's catalyst layer Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-09 Assma El Kaddouri, Lionel Flandin, Corine Bas
The degradation of perfluorinated sulfonic acid ionomer (PFSA) binder in catalyst layer of Proton Exchange Membrane Fuel Cell (PEMFC) was investigated on Membrane-Electrode-Assemblies (MEA) operated up to 10400 h in base load conditions for telecom relay. Soxhlet extractions in water media were performed on the catalyst layer deposited on the Gas Diffusion Layer (GDL). The Soxhlet solutions for anode and cathode sides were analyzed by 19F NMR spectroscopy showing degradation products originating from the ionomer in the catalyst layer. At the cathode side, 1,2,2-tetrafluoro-2-(1,2,2,2-tetrafluoroethoxy)ethanesulfonic acid were clearly identified. This suggests that PFSA binder degradation originated from an H• and/or •OH radical attack of the side chain. The NMR quantification of the degradation products allows a fruitful comparison with the literature. The degradation mechanism of the PFSA binder is different from that of the membrane.
Hydrogen storage properties of the novel crosslinked UiO-66-(OH)2 Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-09 Saisai Chen, Jin Liu, Yongfei Xu, Zhen Li, Tai Wang, Jiong Xu, Zhuo Wang
Metal organic frameworks (MOF) are a type of nanoporous materials with large specific surface area, which are especially suitable for gas separation and storage. In this work, we report a new approach of crosslinking UiO-66-(OH)2 to enhance its hydrogen storage capacity. UiO-66-(OH)2 was synthesized using hafnium tetrachloride (HfCl4) and 2, 5-dihydroxyterephthalic acid (DTPA) through a canonical modulated hydrothermal method (MHT), followed by a post-synthesis modification, which is to form a crosslinking structure inside the porous structure of UiO-66-(OH)2. During the modification process, the phenolic hydroxyl groups on the UiO-66-(OH)2 reacted with methanal, and HCl aqueous solution and triethylamine served as catalyst (the products denoted as UiO-66-H and UiO-66-T, respectively). Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), 13C nuclear magnetic resonance spectroscopy (13C NMR) proved that the crosslinking was formed. The BET specific surface area and the average adsorption pore size of UiO-66-H and UiO-66-T significantly increased after modification. The hydrogen storage capacity of UiO-66-H reached a maximum of 3.37 wt% (16.87 mmol/g) at 77 K, 2 MPa. Hydrogen adsorption enthalpy of UiO-66-T was 0.986 kJ/mol, which was higher than that of UiO-66-(OH)2 (0.695 kJ/mol). This work shows that UiO-66-(OH)2 is a promising candidate for potential application in high-performance hydrogen storage.
The role of interface charge transfer on Pt based catalysts for water splitting Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-09 Shangguo Liu, Shiping Huang
The controllable charge transfer at the interface between substrate and supported metal provides a powerful tool for fine tuning the electronic structure and catalytic activity of supported metal. Aiming at exploring the role of interface charge transfer in cleavage of OH bond in H2O, we performed DFT calculations to investigate H2O splitting on Pt based catalysts: Starting from supported Pt, going to TM13@Pt42 nanoparticles. By choosing different substrates or introducing different electronegative dopants, the amount of charge transfer from Pt can be manipulated. It was found that the charge transfer from Pt to substrate and core metals to shell Pt will influence the ability of Pt atoms to cleavage the OH bonds. Our work reveals that the interface charge transfer can act as one of the microscopic driving forces for the OH bonds cleavage, which will provide useful insight into rational design catalysts for H2O splitting.
Novel Ni–Co–B hollow nanospheres promote hydrogen generation from the hydrolysis of sodium borohydride Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-09 Jie Guo, Yongjiang Hou, Bo Li, Yulei Liu
Ni–Co–B hollow nanospheres were synthesized by the galvanic replacement reaction using a Co–B amorphous alloy and a NiCl2 solution as the template and additional reagent, respectively. The Ni–Co–B hollow nanospheres that were synthesized in 60 min (Ni–Co–B-60) showed the best catalytic activity at 303 K, with a hydrogen production rate of 6400 mLhydrogenmin−1gcatalyst−1 and activation energy of 33.1 kJ/mol for the NaBH4 hydrolysis reaction. The high catalytic activity was attributed to the high surface area of the hollow structure and the electronic effect. The transfer of an electron from B to Co resulted in higher electron density at Co sites. It was also found that Ni was dispersed on the Co–B alloy surface as result of the galvanic replacement reaction. This, in turn, facilitated an efficient hydrolysis reaction to enhance the hydrogen production rate. The parameters that influenced the hydrolysis of NaBH4 over Ni–Co–B hollow nanospheres (e.g., NaOH concentration, reaction temperature, and catalyst loading) were investigated. The reusability test results show that the catalyst is active, even after the fifth run. Thus, the Ni–Co–B hollow nanospheres are a practical material for the generation of hydrogen from chemical hydrides.
Specimen thickness effect on the property of hydrogen embrittlement in single edge notch tension testing of high strength pipeline steel Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-09 Yizhe Li, Baoming Gong, Xiaogang Li, Caiyan Deng, Dongpo Wang
In the study, hydrogen effects on the fracture toughness of an API X90 pipeline steel are investigated considering specimen thickness effects. It is found that the embrittlement of fracture increases with thickness for the hydrogenated specimens. The fracture toughness of hydrogen-free specimens are about 2.9, 5.2 and 11.6 times larger than the hydrogenated ones for B/W = 0.5, 1 and 2, respectively. Digital image correlation (DIC) measurement indicates that as the specimen thickness increases, hydrogen deteriorates drastically the plasticity in the vicinity of the crack tip. A remarkably low dislocation density is observed, indicating hydrogen atom has great influence on the cohesive energy, rather than the dislocation pile-ups. Finally, it is concluded that hydrogen enhanced decohesion (HEDE) mechanism is responsible for the high hydrogen sensitivity to the specimen thickness.
Rapidly mixed combustion of hydrogen/oxygen diluted by N2 and CO2 in a tubular flame combustor Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-05 Baolu Shi, Bo Li, Xiaoyao Zhao, Run Chen, Osamu Fujita, Ningfei Wang
In this study hydrogen flames have been attempted in a rapidly mixed tubular flame combustor for the first time, in which fuel and oxidizer are individually and tangentially injected into a cylindrical combustor to avoid flame flash back. Three different cases were designed to examine the effects of fuel and oxidizer feeding method, diluent property, oxygen content and equivalence ratio on the characteristics of hydrogen flame, including the flame structure, lean extinction limit, flame stability and temperature. The results show that by enhancing mixing rate through feeding system, the range of equivalence ratio for steady tubular flame can be much expanded for the N2 diluted mixture, however, at the oxygen content of 0.21 (hydrogen/air) the steady tubular flame is achieved only up to equivalence ratio of 0.5; by decreasing oxygen content, the lean extinction limit slightly increases, and the upper limit for steady tubular flame establishment increases significantly, resulting in an expanded tubular flame range. For CO2 diluted mixture, the stoichiometric combustion has been achieved within oxygen content of 0.1 and 0.25, for which the burned gas temperature is uniformly distributed inside the flame front; as oxygen content is below 0.21, a steady tubular flame can be obtained from the lean to rich limits; and the lean extinction limit increases from 0.17 to 0.4 as oxygen content decreases from 0.21 to 0.1, resulting in a shrunk tubular flame range. Laminar burning velocity, temperature and Damköhler number are calculated to examine the differences between N2 and CO2 diluted combustion as well as the requirement for hydrogen-fueled tubular flame establishment.
Hydrogen related degradation in pipeline steel: A review Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-06 Enyinnaya Ohaeri, Ubong Eduok, Jerzy Szpunar
To support our increasing energy demand, steel pipelines are deployed in transporting oil and natural gas resources for long distances. However, numerous steel structures experience catastrophic failures due to the evolution of hydrogen from their service environments initiated by corrosion reactions and/or cathodic protection. This process results in deleterious effect on the mechanical strength of these ferrous steel structures and their principal components. The major sources of hydrogen in offshore/subsea pipeline installations are moisture as well as molecular water reduction resulting from cathodic protection. Hydrogen induced cracking comes into effect as a synergy of hydrogen concentration and stress level on susceptible steel materials, leading to severe hydrogen embrittlement (HE) scenarios. This usually manifests in the form of induced-crack episodes, e.g., hydrogen induced cracking (HIC), stress-oriented hydrogen induced cracking (SOHIC) and sulfide stress corrosion cracking (SSCC). In this work, we have outlined sources of hydrogen attack as well as their induced failure mechanisms. Several past and recent studies supporting them have also been highlighted in line with understanding of the effect of hydrogen on pipeline steel failure. Different experimental techniques such as Devanathan–Stachurski method, thermal desorption spectrometry, hydrogen microprint technique, electrochemical impedance spectroscopy and electrochemical noise have proven to be useful in investigating hydrogen damage in pipeline steels. This has also necessitated our coverage of relatively comprehensive assessments of the effect of hydrogen on contemporary high-strength pipeline steel processed by thermomechanical controlled rolling. The effect of HE on cleavage planes and/or grain boundaries has prompted in depth crystallographic texture analysis within this work as a very important parameter influencing the corrosion behavior of pipeline steels. More information regarding microstructure and grain boundary interaction effects have been presented as well as the mechanisms of crack interaction with microstructure. Since hydrogen degradation is accompanied by other corrosion-related causes, this review also addresses key corrosion causes affecting offshore pipeline structures fabricated from steel. We have enlisted and extensively discussed several recent corrosion mitigation trials and performance tests in various media at different thermal and pressure conditions.
Controlled synthesis of MnO2@TiO2 hybrid nanotube arrays with enhanced oxygen evolution reaction performance Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-06 Xia Li, Manru Zhang, Yong Zhang, Cuiping Yu, Wentao Qi, Jiewu Cui, Yan Wang, Yongqiang Qin, Jiaqin Liu, Xia Shu, Ying Chen, Ting Xie, Yucheng Wu
A novel tube-in-tube nanostructure of MnO2@ TiO2 hybrid arrays has been obtained by a facile and controllable chemical bath deposition method. Scrutiny on the hybrid arrays indicates that the chemical bath deposition method favors the growth of the MnO2 nanotubes with different diameter which can modulate the oxygen evolution reaction (OER) activity as well as bandgap width of the hybrid. In terms of OER activity, onset potential (Es) shifts negatively from 0.698 V (vs.Ag/AgCl) of pristine titania nanotube arrays (TNAs) to 0.501 V of the hybrid loaded with 26.6%wt MnO2, and the current density on the hybrid electrode can be significantly enhanced up to 20.87 mA/cm2, almost 97 times higher than that on TNAs electrode (0.214 mA/cm2). Optical absorption measurement suggests that the bandgap width (Eg) can be tuned by loading MnO2 onto the TNAs implying interaction between the MnO2 and TNAs. The MnO2@TiO2 hybrid nanotube arrays may find promising potential in electrochemical water splitting, photocatalysis, thermocatalysis and other sustainable energy applications.
Assessment of steady and unsteady flamelet models for MILD combustion modeling Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-06 F. Chitgarha, A. Mardani
Moderate or intense low-oxygen dilution (MILD) combustion is a novel combustion technology with the comparable chemical and turbulent mixing timescales. In the most of literatures, relatively expensive volume-based models are recommended for this combustion regime while this regime is not completely idealized homogenized reactor and nor strong flamelet like. This paper is focused on the assessment of the lower cost, flamelet approach for MILD condition. In this way, simplifying JHC burner of Dally et al. is considered to model using RANS approach. The effects of inclusion of unity versus non-unity Lewis numbers, radiation heat transfer, and various scalar dissipation rates are evaluated. Results show that the flamelet model may not be totally rejected for the MILD condition because it could still capture flame characteristics relatively acceptable. Choosing an appropriate scalar dissipation rate value is discussed for single flamelet and higher values are recommended by O2 increment. Moreover, considering non-unity Lewis numbers improved species concentration at the jet centerline for low O2 levels. Furthermore, the unsteady flamelet model with radiation had a better prediction for NOx especially for higher O2 Levels.
Electrocatalysis of oxygen reduction when varying the mass ratio of metal nanoparticles to carbon support for catalysts with a 10 to 10 to 80 mol% of Pt and Pd on Ag Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-06 I.E. Pech-Pech, Dominic Gervasio, S.A. Aguila, J.F. Perez-Robles
The reduction of total Pt-loading in a cathode catalyst without sacrificing performance is one of the key objectives for the large-scale commercialization of proton exchange membrane fuel cell (PEMFC) technology. A core-shell type nanostructured catalyst with a Pt-loading 20 times lower than a commercial catalyst is demonstrated herein to be more active for the electrocatalysis of the oxygen reduction reaction (ORR) in acid electrolyte. The weight ratio of metal nanoparticles on carbon support is the key to achieving the highest ORR activity in a series of silver-based catalysts, all with 10 mol percent of Pt and 10 mol percent of Pd over 80 mol percent of silver (Ag) and supported on untreated Vulcan carbon to form an electrocatalyst (Ag@Pt10Pd10/C) with either 5, 10, 20 or 30 wt% of total metals on carbon; which correspond to a Pt concentration around 1, 2, 3 and 5 wt%, respectively. All metal nanostructures on carbon show a similar morphology, size and structure. Thin films of these four Ag@Pt10Pd10/C catalysts on rotating disk electrodes (TF-RDEs) all shown a 4-electrons pathway for the ORR and give higher exchange current densities (jo > 3.8 mA/cm2) than a commercial Etek Pt20/C catalyst (jo = 2.4 mA/cm2). The Ag@Pt10Pd10/C catalyst with 5 wt% of total metals (1 wt% of Pt) on carbon gives the best electrocatalysis; reducing molecular oxygen to water two times faster and generating 25% higher current per milligram of platinum (mass activity) than the commercial catalyst (Pt20/C). Therefore, the Ag@Pt10Pd10/C catalyst with 5 wt% of total metals is a new catalyst for ORR for a PEMFC with a lower Pt loading and cost.
Hydrogen dispersion in a closed environment Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 M. De Stefano, X. Rocourt, I. Sochet, N. Daudey
The highly combustible nature of hydrogen poses a great hazard, creating a number of problems with its safety and handling. As a part of safety studies related to the use of hydrogen in a confined environment, it is extremely important to have a good knowledge of the dispersion mechanism.The present work investigates the concentration field and flammability envelope from a small scale leak. The hydrogen is released into a 0.47 m × 0.33 m x 0.20 m enclosure designed as a 1/15 – scale model of a room in a nuclear facility. The performed tests evaluates the influence of the initial conditions at the leakage source on the dispersion and mixing characteristics in a confined environment. The role of the leak location and the presence of obstacles, are also analyzed. Throughout the test, during the release and the subsequent dispersion phase, temporal profiles of hydrogen concentration are measured using thermal conductivity gauges within the enclosure. In addition, the BOS (Background Oriented Schlieren) technique is used to visualise the cloud evolution inside the enclosure. These instruments allow the observation and quantification of the stratification effects.
Platinum-palladium nanoparticles-loaded on N-doped graphene oxide/polypyrrole framework as a high performance electrode in ethanol oxidation reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Masoume Boulaghi, Hamidreza Ghafouri Taleghani, Mohammad Soleimani Lashkenari, Mohsen Ghorbani
Existing catalysts for ethanol oxidation in direct ethanol fuel cells (DEFC) are faced to significant challenges due to their poor performance and CO like intermediates poisoning tolerance at anode surface. Hence researchers are looking for new electrocatalysts in the ethanol oxidation. In this study, polypyrrole/N-doped graphene oxide (PPy/NGO) nanocomposite was prepared using in-situ polymerization method. Next the platinum-palladium (PtPd) was electrochemically decorated on PPy/NGO nanocomposite surface. In order to ensure the correct preparation of nanocomposite, fourier transform infrared spectroscopy (FT-IR) analysis was carried out to peruse the chemical structure of the nanocomposite and also to investigate their morphology, field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used. The morphology of nanocomposite shows that PPy has penetrated into the space between NGO plates. Disparate electrochemical techniques like cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) were employed to evaluate the oxidation of ethanol. Results showed that PtPd/PPy/NGO exhibits improved electrocatalytic activity and stability for ethanol oxidation. Enhanced active surface area of the PtPd/PPy/NGO electrode (35.1 m2 g−1) contributes to increase in current density and decrease in over potential values in the ethanol oxidation as compared to PtPd electrocatalyst.
Numerical investigation of cold-start behavior of polymer electrolyte fuel cells in the presence of super-cooled water Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Lei Yao, Jie Peng, Jian-bo Zhang, Yang-jun Zhang
In this study, a mathematical model has been developed to simulate the transient cold-start processes of polymer electrolyte fuel cells. The super-cooled water is assumed to exist within the cell. The non-equilibrium water transfer between the membrane and the catalyst layer is considered. The models of water freezing and ice melting in the catalyst layer and gas diffusion layer have been established. For the first time, the randomicity of the freezing process is captured by introducing a freezing probability function. Based on this model, the cold-start processes of a single polymer electrolyte fuel cell starting at various operating and initial conditions have been simulated numerically. The results indicate that the cold-start performance of the cell is determined by the water storage potential of the electrolyte in cathode catalyst layer. For each startup temperature and operating current load, there is a most appropriate initial membrane water content, which corresponds to the longest cell shutdown time. When the cold-start process is failed, the ice is mainly accumulated in the cathode catalyst layer. The ice distribution becomes more non-uniform as the cold-start temperature is lower.
Core/shell Fe3O4@Fe encapsulated in N-doped three-dimensional carbon architecture as anode material for lithium-ion batteries Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Qiang Wu, Cheng Ji, Xiaohui Zhang, Qichang Pan, Jiujun Zhang, Qingyu Li, Hongqiang Wang
Core-shell Fe3O4@Fe nanoparticles embedded into porous N-doped carbon nanosheets was prepared by a facile method with NaCl as hard-template. The three-dimensional carbon architecture built by carbon nanosheets enhance the conductivity of the encapsulated Fe3O4@Fe nanoparticles and strengthen the structure stability suffering from volume expansion during extraction and insertion of lithium ions. Rich Pores enhance the surface between electrode and electrolyte, which short the transmission path of ions and electrons. The core-shell structure with Fe as core further improves charge transferring inside particles thus lead to high capacity. The as-prepared Fe3O4@Fe/NC composite displays an irreversible discharge capacity of 839 mAh g−1 at 1 A g−1, long cycling life (722.2 mAh g−1 after 500th cycle at 2 A g−1) and excellent rate performance (1164.2 and 649.2 mAh g−1 at 1 and 20 A g−1, respectively). The outstanding electrochemical performance of the Fe3O4@Fe/NC composite indicates its application potential as anode material for LIBs.
Improved photocatalytic H2 production assisted by aqueous glucose biomass by oxidized g-C3N4 Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Andrea Speltini, Andrea Scalabrini, Federica Maraschi, Michela Sturini, Ambra Pisanu, Lorenzo Malavasi, Antonella Profumo
Chemically modified g-C3N4 for the photocatalytic H2 evolution from water was explored. Bulk g-C3N4 was treated in hot HNO3 aqueous solution to obtain the oxidized material (o-g-C3N4), tested in water containing glucose as model water-soluble sacrificial biomass, using Pt as co-catalyst, under simulated solar light. The behaviour of o-g-C3N4 was studied in relation with catalyst amount, Pt loading, glucose concentration. Results showed that H2 production is favoured by increasing glucose concentration up to 0.1 M and Pt loading up to 3 wt%, and it resulted strongly enhanced using small amount of o-g-C3N4 (0.25 g L−1). o-g-C3N4 possesses superior photocatalytic activity (∼26-fold higher) compared to pristine g-C3N4, with H2 evolution further improved by ultrasound-assisted exfoliation and evolution rates up to ca. 1370 μmol h−1 per gram of catalyst, with excellent reproducibility (RSD < 6%, n = 3). Significant production was observed also in river water and seawater, with results far better (up to ca. 2500 μmol g−1 h−1) compared to commercial AEROXIDE® P25 TiO2 under natural solar light.
Synthesis of nitrogen-doped MoSe2 nanosheets with enhanced electrocatalytic activity for hydrogen evolution reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Xianpei Ren, Qiang Ma, Pinyun Ren, Yonghua Wang
Benefiting from improved electrical conductivity, the N-doped MoSe2 nanosheets show substantially enhanced HER activity with a lower onset overpotential of approximately −135 mV and a smaller Tafel slope of 62 mV dec−1, which exhibiting enhanced catalytic performance compared with that of pure MoSe2. The success of improving the HER performance via the introduction of N dopant offers a new opportunity in the development of high performance MoSe2-based electrocatalyst.
A novel hydrogen storage medium of Ca-coated B40: First principles study Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Yafei Zhang, Xinlu Cheng
Using first principles study, we have investigated the hydrogen storage capacity of Ca-coated B40. Our result shows that Ca prefers to adsorb on the top hollow center of heptagonal ring of B40 due to the large binding energy of −2.820 eV. Bader charges calculation indicates that charges transfer from Ca to B40 result in an induced electric field so that H2 molecules are polarized and adsorbed onto the surface of B40 without dissociation. The Ca6B40 complex can adsorb up to 30 H2 molecules with average adsorption energy of −0.177 eV/H2 and the hydrogen storage gravimetric density reaches up to 8.11 wt.%, higher than the goal from DOE by the year 2020. These findings will suggest a new and potential structure for hydrogen storage in the future.
Monolithic nanoporous NiFe alloy by dealloying laser processed NiFeAl as electrocatalyst toward oxygen evolution reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Xiaodan Cui, Boliang Zhang, Congyuan Zeng, Hao Wen, Shengmin Guo
In this paper, monolithic nanoporous NiFe electrocatalyst is developed by dealloying a NiFeAl alloy, fabricated by a laser-based manufacturing method, as the electrocatalyst toward oxygen evolution reaction (OER). The nanoporous NiFe alloy displays an improved electrochemical performance by exhibiting an OER current density of 100 mA/cm2 at 442 mV overpotential in the 1 M KOH aqueous solution, which is better than that of laser processed bulk NiFe alloy (464 mV). The structures, crystallinities, and chemical compositions of the nanoporous NiFe electrocatalyst are characterized by SEM, XRD and EDXS. With an activity comparable to the electrocatalysts reported to date, the monolithic nanoporous NiFe electrodes are also highly flexible in mechanical configurations, due to the combined advantages of both laser and dealloying processes, which provide new options for OER electrode design.
Remarkable enhancement of the photocatalytic activity of ZnO nanorod array by utilizing energy transfer between Eosin Y and Rose Bengal for visible light-driven hydrogen evolution Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Luwei He, Xiaomeng Dou, Xiangqing Li, Lixia Qin, Shi-Zhao Kang
In this work, we suggested that an efficient ZnO-based photocatalyst can be prepared utilizing energy transfer among organic dyes for visible light-driven hydrogen evolution. Followed this idea, a photocatalytic system containing Eosin Y, Rose Bengal, ZnO nanorod array and Pt was fabricated. Meanwhile, photocatalytic H2 evolution over the as-prepared photocatalytic system was explored. The results indicate that the visible photocatalytic activity of ZnO nanorod array can be obviously enhanced utilizing the energy transfer between Eosin Y and Rose Bengal. This photocatalytic system possesses high activity for visible light-driven H2 evolution. A rate of H2 evolution of approximate 0.52 L m−2 h−1 was achieved under optimal condition, which is 130% and 58% higher than those of the photocatalytic systems containing individual dye, respectively. The present results may reveal a new strategy for preparation of efficient visible photocatalyst.
Facile synthesis of electrospun C@NiO/Ni nanofibers as an electrocatalyst for hydrogen evolution reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Amutha Chinnappan, Ji Dongxiao, W.A.D.M. Jayathilaka, Chinnappan Baskar, Xiaohong Qin, Seeram Ramakrishna
Hydrogen evolution reaction (HER) is considered to be one of the most important electrochemical reactions from both fundamental and application perspective to produce hydrogen. Polyacrylonitrile (PAN) based carbon (C)@NiO/Ni nanofibers were fabricated via simple electrospinning method. The as-prepared C@NiO/Ni nanofibers were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectra. The SEM and TEM analyses revealed that NiO/Ni nanoparticles distributed on the PAN based carbon nanofibers. EDS, XPS and XRD results confirm the presence of the nanoparticles. The catalytic activity and durability of C@NiO/Ni nanofibers containing different weight ratio of Ni salt content (2%, 3%, & 4%) were examined for HER in 1 M KOH solution. It has been observed that C@NiO/Ni nanofibers containing Ni content (4%) showed the highest catalytic activity. It indicates that the catalytic activity of electrocatalyst can be enhanced by increasing the effective active sites. Noteworthy to mention here that the nanofibers catalyst reached a current density of 60 mA/cm2. The as-prepared catalyst showed remarkable stability up to 22 h and retained 99% of its initial activity even after 16 h of reaction.
Effect of UV irradiation on PC membrane and use of Pd nanoparticles with/without PVP for H2 selectivity enhancement over CO2 and N2 gases Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Rajesh Kumar, Kamakshi, Shivani Shisodia, Manoj Kumar, Kamlendra Awasthi
The hydrogen-based economy is one of the possible approaches toward to eliminate the problem of global warming, which are increases because of the gathering of greenhouse gases. Palladium (Pd) is well-known material having a strong affinity to the hydrogen absorbing property and thus appropriate material to embed in the membrane for the improvement of selective permeation of hydrogen gas. In present work, we have functionalized polycarbonate (PC) membranes with the help of UV irradiation to embed the Pd nanoparticles in pores as well as on the surface of the PC membrane. Use of Pd Nanoparticles is helpful to enhance the H2 selectivity over other gases (CO2, N2, etc.). Also, the UV based modification of membrane increases the attachment of Pd Nanoparticles. Further to enhance the Pd nanoparticles attachment, we used PVP binder with Pd nanoparticles solution. Gas permeability measurements of functionalized PC membranes have been carried out, and better selectivity of hydrogen has been found in the functionalized and Pd nanoparticle binded membrane. PC membrane with 48 h UV irradiated and Pd NPs with PVP have been found to have maximum selectivity and permeability for H2 gas. All the samples being characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and UV–Vis spectroscopy for their morphological and structural investigation.
In-situ synthesis of well dispersed CoP nanoparticles modified CdS nanorods composite with boosted performance for photocatalytic hydrogen evolution Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Junfang Wang, Peifang Wang, Chao Wang, Yanhui Ao
Development of photocatalysts with characters of low-cost, environment friendliness, visible light response and good performance is vital for the transformation of solar energy into hydrogen fuel. Here, we constructed CoPCdS nanorods hybrid composites via a novel two-step in-situ growth method for the first time. The obtained CoPCdS composites exhibited remarkably enhanced photocatalytic performance and excellent stability in comparison with bare CdS nanorods. Notably, the optimum H2 evolution rate of 1 wt%CoPCdS was 9.11 times higher than that of pristine CdS. The apparent quantum efficiency of the photocatalyst was calculated to be 11.6%. The superior activity of this material could be attributed to the role of well dispersed CoP nanoparticles and the intimate interface between CoP cocatalysts and CdS nanorods, which efficiently accelerated the separation and transfer of photogenerated electrons. This work provided a new in-situ growth method for the preparation of transition metal phosphides coated photocatalysts with boosted photocatalytic activity of hydrogen evolution.
Nitrogen-doped graphene-supported zinc sulfide nanorods as efficient Pt-free for visible-light photocatalytic hydrogen production Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-07 Majid Azarang, Mehran Sookhakian, Mousa Aliahmad, Masoumeh Dorraj, Wan Jeffrey Basirun, Boon Tong Goh, Yatimah Alias
Nitrogen-doped graphene-ZnS composite (NG-ZnS) was synthesized by thermal treatment of graphene-ZnS composite (G-ZnS) in NH3 medium. In the second step, the as-synthesized samples were deposited on indium tin oxide glass (ITO) by electrophoretic deposition for photocatalytic hydrogen evolution reaction. The as-prepared NG-ZnS-modified ITO electrode displayed excellent photocatalytic activity, rapid transient photocurrent response, superior stability and high recyclability compared to the pure ZnS and G-ZnS-modified ITO electrode due to the synergy between the photocatalytic activity of ZnS nanorods and the large surface area and high conductivity of N-graphene.
The catalytic effect of the Au(111) and Pt(111) surfaces to the sodium borohydride hydrolysis reaction mechanism: A DFT study Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 A.E. Genç, A. Akça, B. Kutlu
In this research, hydrolysis mechanism of sodium borohydride (NaBH4) have been studied theoretically on Au (111) and Pt (111) noble metal surfaces by periodic density functional theory calculations. Elementary reaction steps have been generated based on study of borohydride oxidation. Reaction intermediates which have plethora of hydroxyl (OH) radical(s) have been produced by decomposition of water molecule(s). In order to investigate surface effect, we have followed two different routes. The first route is that the atomic and molecular structures in the reaction steps have been optimized in 3-d box without a catalyst. At second one, they were interacted with the Au (111) and Pt (111) surfaces to compare relative behavior with reference to the non-catalytic medium. The relative energy diagrams were produced by relative energy differences which is useful to generate energy landscape using required/released energies in order to pursue the reaction. Three main peaks that means considerable energy changes have been observed to proceed the reaction in the non-catalytic medium. Then, changes in the energy differences depending on surfaces have been discussed. Although acquired relative energies are not within chemical accuracy, they are very successful to show the affect of the OH radical concentration to the potential energy diagram. Pt (111) surface have been found more reactive than Au (111) surface for Sodium Borohydride Hydrolysis reaction, as it is obviously coherent with the literature.
Low voltage water electrolysis: Decoupling hydrogen production using bioelectrochemical system Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 Pierre Belleville, Francois Guillet, Alessia Pons, Jonathan Deseure, Gérard Merlin, Florence Druart, Julien Ramousse, Elisa Grindler
Decoupling water electrolysis using mediator is an interesting way to produce pure hydrogen. The present work validates the proof of concept of decoupled electrolyser associated with a bioelectrochemical system (MFC-DES) through a redox flow mediator (potassium hexacyanoferrate (KHCF)). Low voltage (1 V) hydrogen production was achieved with a current density up to 25 mA cm−2. Regeneration of the mediator was performed by glucose fed microbial fuel cells. The oxidation rate of KHCF in the electrolyser is, at least, an order of magnitude higher than the reduction rate in MFC cascade fed system. MFC-DES is thus a promising set up as it desynchronizes limited microbial rate and hydrogen production, generate value from wastewater and reduce energetic cost of water electrolysis.
Hydrogen production from glycerol steam reforming over nickel catalysts supported on alumina and niobia: Deactivation process, effect of reaction conditions and kinetic modeling Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 João Paulo da S.Q. Menezes, Robinson L. Manfro, Mariana M.V.M. Souza
Ni catalysts were prepared by wet impregnation of three different supports: alumina, niobia and 10 wt.% niobia/alumina, prepared by (co)precipitation. The catalysts were evaluated on steam reforming of glycerol at 500 °C, for 30 h. The catalyst supported on Nb2O5/Al2O3 presented the best performance, with higher conversion into gas (80%) during all reaction time and hydrogen yield of 50%. Alumina supported catalyst showed higher deactivation and lower hydrogen yield. All catalysts showed coke formation, but it was formed in larger amount on the catalysts supported on single oxides. A depth study was conducted to evaluate the effect of reaction variables as space velocity, glycerol concentration in feed and temperature on the catalytic performance of the Nb2O5/Al2O3 catalyst. Kinetic study was also performed for this catalyst using two different approaches, obtaining glycerol and steam orders, as well as the apparent activation energy.
Synthesis, characterization and photocatalytic evaluation of potassium hexatitanate (K2Ti6O13) fibers Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 M.A. Escobedo Bretado, M.A. González Lozano, V. Collins Martínez, A. López Ortiz, M. Meléndez Zaragoza, R.H. Lara, C.U. Moreno Medina
Potassium hexatitanate has been barely studied as a photocatalytic material for the hydrogen production from water splitting. The aim is to synthesize and characterize K2Ti6O13 fibers in order to evaluate their photocatalytic activity. Materials were characterized by XRD, BET, UV–Vis and SEM. Fibers were produced with sizes varying from 12 to 35 μm in length and 260–530 nm in diameter, as well as with a specific surface area of 4.1 m2/g and 2.3 m2/g for a heat treatment at 900 °C (C21) and 1000 °C (C22), respectively. Band gap energies for these titanates fall within the visible spectrum 3.23 eV (C21) and 3.28 eV (C22), respectively. Maximum hydrogen production was achieved by (C21) with 2387 μmolH2/gcat, while the lowest production was observed for sample (C22) with 1538 μmolH2/gcat at 8 h of irradiation. Crystals of K2Ti6O13 exhibited high photocatalytic activity and they can be considered as potential photocatalysts for H2 production.
Prediction of turbulence radiation interactions of CH4H2/air turbulent flames at atmospheric and elevated pressures Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 Xiao Yang, Zhihong He, Shikui Dong, Heping Tan
Predicting thermal radiation for turbulent combustion highlights the significance of turbulence radiation interactions (TRI). Thermal radiation behaviors of methane/hydrogen flames under elevated pressures are investigated numerically using the developed TRI module integrated into CFD codes. The updated non-gray weighted sum of gray gases model is used to calculate the radiative properties of participating media. TRI effects have been analyzed with 0%–50% volumetric fraction of hydrogen in the methane/hydrogen blended fuels under 1–5 atm working pressures. Employing the radiation model considering TRI achieves closer predicted consistency to the experimental data. Only thermal radiation makes the flame temperature dropped about 60–140 K, while the predicted radiative source term calculated with TRI is higher than that without TRI, which results in a colder flame (approximately 13–60 K lower). The impact of TRI on the radiation behavior is enhanced in hydrogen-enriched high-pressure flame as the predicted radiation heat flux and radiative source term are increased above 25% than that without TRI. On account of TRI effect, the net radiative heat loss increases almost 50% at elevated pressure. The strong radiation of participating media in methane/hydrogen flames under elevated pressures emphasizes the importance of TRI effect on accurate predictions of thermal radiation and NO emission.
High performance hybrid supercapacitors with LiNi1/3Mn1/3Co1/3O2/activated carbon cathode and activated carbon anode Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 Seung-Hwan Lee, Tae-Ho Lee
Hybrid supercapacitors have been studied as a next generation energy storage device that combines the advantages of supercapacitors and batteries. One important challenge of hybrid supercapacitors is to improve energy density (8.9–42 Wh/kg) with maintaining excellent power density (800–7989 W/kg) and cyclability (98.9% after 9000 cycles). Herein, we demonstrate an approach to design hybrid supercapacitors based on LiNi1/3Mn1/3Co1/3O2 (NMC)/activated carbon (AC) cathode and AC anode (NMC/AC//AC). The NMC/AC//AC hybrid supercapacitors shows outstanding electrochemical performances due to the enhanced energy and power densities. These findings suggest that the NMC/AC cathode is an effective method for high performance hybrid supercapacitors.
Thermocatalytic decomposition of methane over mesoporous Ni/xMgO·Al2O3 nanocatalysts Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 Ali Rastegarpanah, Mehran Rezaei, Fereshteh Meshkani, Hongxing Dai, Hamidreza Arandiyan
This paper describes a facile method to produce mesoporous nanostructure Ni/Al2O3, Ni/MgO, and Ni/xMgO.Al2O3 (x: MgO/Al2O3 molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N2 adsorption/desorption, hydrogen temperature-programmed reduction (H2-TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al2O3 molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m2 g−1. The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al2O3 catalyst calcined at 600οC possessed an acceptable methane conversion (∼60%) under the harsh reaction conditions (GHSV = 48000 (mL h−1 gcat−1)).
Boosting the capacitance of NiCo2O4 hierarchical structures on nickel foam in supercapacitors Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 Hongmei Du, Yeyu Li, Feifei Ding, Jinsheng Zhao, Xianxi Zhang, Yunwu Li, Ruijuan Zhao, Mengting Cao, Tiantian Yu, Xuejuan Xu
A facile method of directly growing NiCo2O4 hybrid hierarchical nanostructures on nickel foam is developed by a hydrothermal and post heat-treatment method without using any surfactant, stabilizer or organic binder. Due to the rich porous nanostructures, relative large specific surface area (177.71 m2 g−1) of the NiCo2O4 hybrid structure and efficient electrical contact with the conductive nickel substrate, the NiCo2O4NF hybrid electrode shows significantly enhanced specific capacitance (3105.1 F g−1 at 1 A g−1), outstanding rate properties (1621.3 F g−1 at 20 A g−1 and 1191.5 F g−1 at 50 A g−1) and high energy density (95.26 Wh kg−1). This facile and effective design method opens up new possibilities for producing binder-free electrodes in high-performance electrochemical supercapacitors and miniaturized devices.
Facile in-situ formation of high efficiency nanocarbon supported tungsten carbide nanocatalysts for hydrogen evolution reaction Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 Cheng Liu, Yan Wen, Liangxu Lin, Haijun Zhang, Xifei Li, Shaowei Zhang
Electrochemical hydrogen evolution reaction (HER) is one of the key techniques for hydrogen production. Much great effort has been made so far to develop highly efficient HER catalysts to replace expensive precious metals (e.g. Pt). Unfortunately, the synthesis processes were generally not cost-effective and/or scalable. So it is highly desirable to develop a facile technique to enhance HER activity of conventional inexpensive but less active materials. In this work, monodispersed tungsten carbide (WC) nanoparticles (<5 nm) were in-situ formed/anchored on nanosized carbon black (CB) and carbon nanotube (CNT) via a simple low temperature molten salt synthesis technique. Owing to this special hybrid structure, both the exposed surface area of active species and the electrical conductivity of the catalysts were increased effectively, making the catalysts perform considerably better in HER than pure WC and WC based catalysts prepared via other conventional routes. WC nanocrystals in-situ formed/anchored on CNTs showed small onset overpotential (90 mV), low Tafel slope (69 mV dec−1), high current density (93.4 and 28 mA cm−2 at 200 and 300 mV, respectively) and excellent stability (remaining stable even after 3000 cycles). Such a performance is one of the best among those of WC based electrocatalysts developed to date. We demonstrate here significantly improved HER performances of inexpensive tailored WC materials, along with a facile synthesis strategy which could be also readily extended to prepare a range of other types of mono-dispersed nanocatalysts for more potential applications.
Study of hybrid energy system coupling fuel cell, solar thermal system and photovoltaic cell Int. J. Hydrogen Energy (IF 4.229) Pub Date : 2018-07-04 Ahmad Haddad, Mohamad Ramadan, Mahmoud Khaled, Haitham Ramadan, Mohamad Becherif
The present work examines the combination of solar energy systems with Fuel cell. Indeed, fuel cells are green storage systems without any pollution effects. They are supplied by oxygen and hydrogen to produce electricity. That is why it is inescapable to find a source of hydrogen in order to use fuel cell. Several techniques can be adopted to produce hydrogen depending on the availability and the cost of the sources. One of the most utilized techniques is electrolysers. They allow to obtain hydrogen from water by several technologies among them proton exchange membrane (PEM) which is considered in this work. On the other hand, electrolysers need electrical power to operate. A green-green energy system can be constructed by using a renewable energy source to supply fuel cell trough electrolysers. A comparison between two solar systems (Photovoltaic and Parabolic Trough) coupled to fuel cell is performed. A case study on the Lebanese city of Tripoli is carried out. The study shows the performance of each of both combined systems for different parameters and proposes recommendations depending on the considered configuration.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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