Iron and cobalt hydroxides: Describing the oxygen evolution reaction activity trend with the amount of electrocatalyst Electrochim. Acta (IF 4.798) Pub Date : 2018-04-12 Javier Quiñonero, Roberto Gómez
Although the amount of oxygen evolution electrocatalyst is a factor determining its efficiency, its fundamental correlation with activity remains unclear. To address this issue, we take advantage of a urea-based chemical bath deposition method (CBD) that enables to control the amount of electrocatalyst (Fe(OH)2 and α-Co(OH)2) deposited on conducting glass. The thickness of the resulting films, whose use in electrocatalysis is unprecedented, is tuned by controlling the deposition time. The turnover frequency (TOF) for O2 generation decreases drastically as the electrocatalyst amount increases from equivalent coverages of 3.5 monolayers (ML) for Fe(OH)2 and of 0.06 ML for α-Co(OH)2 electrodes. The contrasting behavior of both hydroxides comes from the different structure of the incipient deposits, formed by small acicular nanoparticles in the case of Fe(OH)2 and larger flat microparticles in the case of α-Co(OH)2. The former structure allows a large fraction of the Fe sites to be in direct contact with solution, while such a fraction rapidly diminishes with loading for α-Co(OH)2. In addition, the resulting Co(OH)2 electrodes show TOFs similar or higher than those of electrodes prepared by more complex routes. The optimum ultrathin films are remarkably stable in alkaline media, showing that the preparation of efficient electrocatalysts for oxygen evolution with an extremely small amount of metal through a novel, facile and scalable CBD is possible.
The combined effect of CaF2 coating and La-doping on electrochemical performance of layered lithium-rich cathode material Electrochim. Acta (IF 4.798) Pub Date : 2018-04-12 Min Li, Yi Zhou, Xiaoyan Wu, Lei Duan, Chunming Zhang, Fang Zhang, Dannong He
This work provides a new strategy for using the combined effect of coating-CaF2 and La-doping to improve the electrochemical performance of lithium-rich layer material. Here, La-doping in metal transition(MT) layer is employed to block the migration channel of TM ions and stabilize the crystal structure, and coating-CaF2 on the surface of lithium-rich layer oxide material is employed to retard the side reaction between active material and electrolyte. Benefiting from the combined effect of coating-CaF2 and La-doping, CaF2 coated Li1.2Mn0.52Ni0.13Co0.13La0.02O2 exhibits excellent cycling performance and voltage stability. CaF2 coated Li1.2Mn0.52Ni0.13Co0.13La0.02O2 delivers the initial discharge capacity of 227.1 mAh g−1 at 0.5 C. After 100 cycles, its retention of discharge capacity is 93.9%, and its voltage decay is only 0.203 V. This connecting mechanism of coating and doping, which can avoid the insufficient of single coating or single doping, is very helpful to develop effective strategies for the modification of Li-rich oxide materials.
Three-dimensional reduced graphene oxide/carbon nanotube nanocomposites anchoring of amorphous and crystalline molybdenum sulfide: Physicochemical characteristics and electrocatalytic hydrogen evolution performances Electrochim. Acta (IF 4.798) Pub Date : 2018-04-12 Yali Guo, Rui Wang, Xing Xu, Yanan Shang, Baoyu Gao
The three-dimensional (3D) reduced graphene oxide/carbon nanotube nanocomposites (rGO/CNTs nanocomposites) and reduced graphene oxide nanocomposites (rGO nanocomposites) were anchored with amorphous MoSx, forming the MoSx-rGO/CNTs and MoSx-rGO nanocomposites. Their hydrogen evolution reaction (HER) activities were intensively evaluated. Results indicated that the rGO/CNTs nanocomposite provided more sites for the amorphous MoSx as compared with that of CNTs nanocomposite. Raman spectra of MoSx-rGO and MoSx-rGO/CNTs nanocomposites confirmed the amorphous state of MoSx in all MoSx anchored nanocomposites. TEM and SEM morphology indicated that the amorphous MoSx was well-dispersed on the rGO/CNTs and rGO nanocomposites. The amorphous MoSx nanoparticles in MoSx-rGO/CNTs and MoSx-rGO nanocomposites could provide more S atoms at their edges, and therefore greatly improve the HER activity. HER performances indicated that the rGO/CNTs and rGO nanocomposites anchored with crystalline MoS2 exhibited poor HER performance. In contrast, MoSx-rGO/CNTs and MoSx-rGO nanocomposites anchored with a small amount of MoSx exhibited the excellent HER activity (179 mV of overpotential at 10 mA cm−2). Results also indicated that the HER activities of the MoSx-@rGO nanocomposites were a bit smaller than those of MoSx-rGO/CNTs nanocomposites. The CNTs in the rGO/CNTs nanocomposites would improve the intimate electrolyte/electrode contact and promote the high-rate charge transfer, which further strengthened their electrocatalytic hydrogen evolution performances.
Electrochemically synthesised xanthone-cored conjugated polymers as materials for electrochromic windows Electrochim. Acta (IF 4.798) Pub Date : 2018-04-11 H.F. Higginbotham, M. Czichy, B.K. Sharma, A.M. Shaikh, R.M. Kamble, P. Data
In this work, we present the electrochemical polymerisation process of triarylamine-xanthone derivatives and behaviour of the formed polymers using various potentiodynamic techniques. The formed electropolymers have limited conjugation but show very promising electrochromic behaviour. Furthermore, by coupling the electrochemical analysis with each polymer's spectroscopic output, we were able to evaluate doping processes and the type of charge carriers formed. Through careful analysis, we were able to describe the electropolymerisation process and formed triarylamine-based polyxanthone derivatives. The polymers were found to exhibit good stability and good colouration efficiency to suggesting that they have potential application in electrochromic devices.
Heterogeneously catalyzed two-step cascade electrochemical reduction of CO2 to ethanol Electrochim. Acta (IF 4.798) Pub Date : 2018-04-11 Nolan Theaker, Jacob M. Strain, Bijandra Kumar, J. Patrick Brian, Sudesh Kumari, Joshua M. Spurgeon
Electrochemical reduction of CO2 to liquid fuels is a promising route to a carbon-neutral, energy-dense storage of intermittent renewable electricity. However, electrocatalysts generally suffer from high overpotential and poor selectivity for multi-carbon products such as ethanol, and efforts to enhance such catalysts are limited by scaling relations which inhibit a simultaneous optimization of each elementary electrochemical step. In this work, the multistep proton-coupled electron-transfer reaction for the conversion of CO2 to C2H5OH was strategically divided into two independently optimized steps in a sequential cascade reaction using heterogeneous electrocatalysts to convert CO2 to CO and CO to C2H5OH within a single integrated electrochemical system. The exclusion of CO2 reactant from the second-stage electrolyzer was observed to be critical for maintaining appreciable ethanol selectivity. The cascade system produced C2H5OH at an overall faradaic efficiency of 11.0% at an average applied potential of −0.52 V vs. RHE, making it highly competitive with known single-step electrocatalysts for ethanol production from CO2. This performance was despite limited conversion of the intermediate CO between cascade steps (∼6.4%), and reactor design improvements to enhance the conversion could lead to significantly enhanced ethanol production performance.
Porous oxide electrocatalysts for oxygen evolution reaction prepared through a combination of hydrogen bubble templated deposition, oxidation and galvanic displacement steps Electrochim. Acta (IF 4.798) Pub Date : 2018-04-11 Nicola Comisso, Lidia Armelao, Sandro Cattarin, Paolo Guerriero, Luca Mattarozzi, Marco Musiani, Marzio Rancan, Lourdes Vázquez-Gómez, Enrico Verlato
Porous oxide layers active in the oxygen evolution reaction (OER) were prepared with the following sequence of steps: (i) porous Pb was produced by cathodic hydrogen bubble templated electrodeposition; (ii) Pb was partially converted to its oxides; (iii) Co3O4 shells were formed on the surface of lead/lead oxides nanowires by spontaneous galvanic displacement reactions. The effect of deposition current density and charge on the porous Pb morphology was studied. Deposits with extended surface areas were obtained and then oxidized in neutral Na2SO4 solutions. Pb and PbO2, initially coexisting in oxidized samples, underwent a spontaneous reaction leading to the formation of Pb3O4. Both PbO2 and Pb3O4 spontaneously reacted with Co2+ to yield Co3O4 layers. Co-modified electrodes described in this work had higher activity in oxygen evolution reaction (OER) than those obtained by submitting to galvanic displacement porous PbO2 layers prepared by oxygen bubble templated anodic deposition.
Ternary polymer solar cells based on two highly efficient fullerene acceptors with high efficiency and stability under long-time thermal annealing treatment Electrochim. Acta (IF 4.798) Pub Date : 2018-04-11 Shengli Niu, Zhiyong Liu, Qiang Liu, Ning Wang
By introducing a dihydronaphthyl-based C60 bisadduct (NCBA) small molecule acceptor as an third component materials to typical polymer donor:fullerene acceptor binary polymer solar cells (PSCs), we demonstrate that the short-circuit current density (JSC), open circuit voltage (VOC), fill factor (FF), power conversion efficiency (PCE), and thermal stability can be enhanced simultaneously. The ternary photoactive layer enhances photogenerated charge-carrier generation efficiency through complementary short wavelength visible-light absorption between the donor molecule and fullerene acceptors. Simultaneously, the improved PSC performance is mainly attributed to the enhanced exciton dissociation and charge-carrier transport. Furthermore, we find that the NCBA as third component materials can reduce charge-carrier recombination and enhancement of thermal stability in ternary PSCs as well. The results bring new insight into the future development of high-efficiency ternary PSCs.
Electronic properties and corrosion resistance of passive films on austenitic and duplex stainless steels Electrochim. Acta (IF 4.798) Pub Date : 2018-04-10 G. Tranchida, M. Clesi, F. Di Franco, F. Di Quarto, M. Santamaria
Passive films were grown at constant potential in acidic (pH 2) and alkaline (pH 13) solutions on chromium, AISI 304L, AISI 316L and Duplex stainless steels. Passive films on chromium grow following a high field mechanism considering the presence of dissolution phenomena. According to the photoelectrochemical characterization, passive films on Cr have a bandgap of 3.4 eV when formed in acidic solution, and of 2.4 eV when formed in alkaline solution due to the formation of Cr(OH)3. These films result to be poorly stable against anodic dissolution due to a very anodic flat band potential. Conversely, impedance and photoelectrochemical measurements proved that passive films on stainless steels are chromium rich oxide n-type semiconductors with a very high polarization resistance. Their band gap depends on the pH of the passivation solution and the SS composition.
O2 electrochemistry on Pt: A unified multi-step model for oxygen reduction and oxide growth Electrochim. Acta (IF 4.798) Pub Date : 2018-04-10 Barathram Jayasankar, Kunal Karan
Oxygen electrochemistry on platinum comprises of three well-known, phenomena - oxygen reduction reaction (ORR), platinum oxide cyclic voltammetry (CV) and platinum oxide growth. Many of the elementary reaction steps are common to the three reaction systems but usually separate kinetic models for the three phenomena are reported in the literature. In this paper, we present a single reaction framework comprising multistep mechanism, based on suitable modification of double trap kinetic model , that captures the key characteristics of the ORR, CV and oxide growth. Comparison between experimental data and model as well as other models is presented in this work.
Electrosynthesis of polypyrrole-vanadium oxide composites on graphite electrode in acetonitrile in the presence of carboxymethyl cellulose for electrochemical supercapacitors Electrochim. Acta (IF 4.798) Pub Date : 2018-04-10 Erhan Karaca, Kadir Pekmez, Nuran Özçiçek Pekmez
One-step electrochemical synthesis of polypyrrole-vanadium oxide (PPy-VOx) composites was performed on the Vanadium-intercalated pencil graphite (PG) surface in an acetonitrile solution with the presence of carboxymethyl cellulose (CMC). Both intercalated surface and composite coating were characterized using SEM-EDX Spectroscopy and X-Ray Diffraction (XRD) techniques. The capacitive properties of the coating were elaborated in an H2SO4/water medium using galvanostatic charge–discharge, potential cycling, and electrochemical impedance spectroscopy methods in comparison with the coatings prepared without additives. While V-intercalation provides a significant increase in the specific capacitance, the carboxymethyl cellulose enhances the cyclic performance of the composite. The improvement at the capacitance of the composite may be due to the homogenous distribution as well as the synergetic effect between PPy and VOx. The capacitive properties were studied in aqueous solutions of H2SO4 and Li2SO4, and in an acetonitrile solution of HBF4/TBABF4. The specific capacitance value of the composite coating on the V-intercalated pencil graphite was determined as 204 F g−1 in an acetonitrile solution of HBF4/TBABF4 for a mass loading of 10.0 mg cm−2 at 2.0 A g−1, when the capacitance of bare graphite was subtracted. The two-electrode supercapacitors composed of both asymmetric and symmetric configurations were also prepared and examined in an acetonitrile/adiponitrile solution of HBF4/TBABF4. The charge–discharge results for asymmetric supercapacitor reveal that the PPy-VOx-CMC composite coating (20 mg cm−2) on V-intercalated graphite paper represents a high energy density of 18 Wh.kg−1 and a high power density of 0.43 kW kg-1 at 0.5 A g−1, as well as a stable cycle life at the potential range of 1.2 V.
Computational analysis and experimental evidence of two typical levelers for acid copper electroplating Electrochim. Acta (IF 4.798) Pub Date : 2018-04-10 Zhiqiang Lai, Shouxu Wang, Chong Wang, Yan Hong, Yuanming Chen, Huaiwu Zhang, Guoyun Zhou, Wei He, Kehua Ai, Yongqiang Peng
In this work, the leveling effect of two typical levelers for copper electroplating, Janus Green B (JGB) and polymerizates of imidazole and epichlorohydrin (IMEP) are both analyzed through computational calculations and electrochemical experiments. Frontier Molecule Orbital (FMO) and the electrostatic potential (ESP) of JGB, IMEP and accelerated complex MPS-Cu(I) are calculated and visualized by Density Functional Theory (DFT) method to predict the preferable reaction sites for electrophilic or nucleophilic attack and the corresponding interactions. The adsorption processes of JGB and IMEP with MPS-Cu(I) on copper surface are examined through molecular dynamics (MD) simulation. According to the results of calculations, we conclude that IMEP is the better candidate for electroplating at high current density in comparison with JGB. The results from electrochemical tests validate that MPS has both synergistic and antagonistic effect with IMEP and has an antagonistic effect with JGB. Electroplating tests confirms that the system with IMEP exhibits a better leveling effect at higher current density. In addition, relatively higher ESP value is preferred for a leveler in a large current density electroplating.
Self-powered sensor for tannic acid exploiting visible LED light as excitation source Electrochim. Acta (IF 4.798) Pub Date : 2018-04-10 Fernanda Gabrielle Soares da Silva, Greicy Kelly Cerqueira dos Santos, Sakae Yotsumoto Neto, Rita de Cássia Silva Luz, Flávio Santos Damos
The present work describes the development of a self-powered photoelectrochemical sensor for the determination of tannic acid (TA) based on a TA-sensitized TiO2 (TA/TiO2) as photoanode and Cu2O/ZnO/FTO photocathode to water reduction. The self-powered cell was comprised of a photoanode and a photocathode separated in two chambers to generate the suitable power output under irradiation from a visible LED light driving the tannic acid sensing process. The electronic characteristics of TA/TiO2/FTO photoanode and Cu2O/ZnO/FTO photocathode were evaluated by electrochemical impedance spectroscopy. The principle of the self-powered photoelectrochemical cell is based on water reduction in the cathodic chamber on the Cu2O/ZnO/FTO photocathode while TA is oxidized in the anodic chamber to generate a cell output which depends on the concentration of TA in the anodic compartment. Under optimized conditions, the cell presented a wide linear response range for TA from 1 μmol L−1 up to 500 μmol L−1, demonstrating that the capability of the proposed system to generate power can be modulated by the TA concentration.
Ultrathin all-solid-state supercapacitor devices based on chitosan activated carbon electrodes and polymer electrolytes Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Matthew Genovese, Haoran Wu, Alvin Virya, Jak Li, Peizhi Shen, Keryn Lian
Two of the most promising current trends in supercapacitor research, (i) the development of biomass based carbon electrodes, and (ii) the transition to solid thin flexible form factors via polymer electrolytes are combined and investigated. A high surface area (3312 m2 g−1) mesoporous activated carbon was synthesized from chitosan biomass and showed excellent capacitive behaviour in a range of acidic, neutral, and alkaline liquid electrolytes. The performance in the neutral Li2SO4 electrolyte system was particularly promising with the chitosan AC electrodes showing a high capacitance (264 F g−1) similar to the values in acidic and alkaline electrolytes but with a much larger 1.8 V potential window. The chitosan AC also proved compatible with a series of solid polymer electrolytes through a detailed comparison in which solid-state chitosan supercapacitor devices were shown to closely mimic the capacitance and high rate performance of their liquid counterparts. This is an important finding as it demonstrates that high surface area, intricately porous activated carbon networks can still be readily accessible to solid electrolytes. Combining the chitosan AC with a Li2SO4-polyacrylamide (PAM) solid electrolyte enabled the fabrication of ultra-thin (<0.38 mm) supercapacitor devices which demonstrated a capacitance close to 3 times greater than analogues prepared with a commercially available microporous AC (YP-50). These chitosan devices also demonstrated high volumetric energy density (1.6 mWh cm−3) and power density (0.8 W cm−1) comparable to state-of-the-art SC devices utilizing much more expensive materials. This material system represents a simple and cost effective approach for the design of next-generation solid thin, flexible energy storage devices.
Carbon quantum dots based charge bridge between photoanode and electrocatalysts for efficiency water oxidation Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Xiao Jiang, Zemin Zhang, Junfeng Mei, Dongyan Han, Mingzheng Xie, Fangcong Wang, Erqing Xie, Weihua Han
SOFC operation with carbon oxides: Experimental analysis of performance and degradation Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Bernhard Stoeckl, Vanja Subotić, Michael Preininger, Hartmuth Schroettner, Christoph Hochenauer
The high fuel flexibility of solid oxide fuel cells allow them to be operated using carbonaceous fuels. This work focuses on a supply of carbon monoxide on large planar single cells, since detailed investigations thereof are rarely found in literature. In the course of this project, stable cell operation was achieved with CO/CO2/N2CO/CO2/N2 gas compositions at 800 °C and 750 °C as well as acceptable performance, though test results with H2/H2O/N2H2/H2O/N2 gas mixtures were not reached. Electrochemical impedance measurements revealed high polarization resistances to be the cause of this differences in performance. The combination of carbon monoxide and hydrogen as reactants in fuel mixtures results in rapid performance degradation: a performance reduction of 27% was recognizable within 6 h. Additionally, a 100 h test at 700 °C with <img height="16" border="0" style="vertical-align:bottom" width="204" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0013468618307680-si3.gif">CO/CO2/N2=20/10/70vol% in polarization conditions (50 mA cm−2) is also presented, wherein there was continuous degradation at a rate of 17.2% over 100 h. Scanning electron investigations showed significant influences on the microstructure as carbon led to an enlargement of the nickel components and the coverage of the catalyst surfaces, respectively.
NMR spectroelectrochemistry in studies of hydroquinone oxidation by polyaniline thin films Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Xiao-Ping Zhang, Wen-Long Jiang, Shuo-Hui Cao, Hui-Jun Sun, Xue-Qiu You, Shu-Hui Cai, Jiang-Li Wang, Cheng-Sen Zhao, Xin Wang, Zhong Chen, Shi-Gang Sun
In this paper, we developed a direct way for the study of hydroquinone oxidation through in situ electrochemistry-combined nuclear magnetic resonance (EC-NMR). Electro-polymerization-induced nano-polyaniline film was utilized as the catalyst in the process of electrochemical oxidation of hydroquinone. In situ EC-NMR provides a powerful tool to probe products distribution and reaction rate, which could be useful to investigate electro-catalytic mechanism and evaluate the electro-catalytic capacity. To study the influence of both protic and aprotic media in the electrocatalytic process, we mixed water and dimethylsulfoxide to mimic possible real-life electrochemical environments. The proposed in situ EC-NMR is capable of quantitatively monitoring the generation of products under varied solvent composition and pH values. A positive effect to electro-catalysis capacity is observed when the concentration of DMSO or water is increased from the volume equivalent point, implying that there should be a competition between protic and aprotic media, which can be characterized by EC-NMR technique.
Enhancing rate capability of amorphous nickel phosphate supercapattery electrode via composition with crystalline silver phosphate Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Fatin Saiha Omar, Arshid Numan, Shahid Bashir, Navaneethan Duraisamy, R. Vikneswaran, Yueh-Lin Loo, K. Ramesh, S. Ramesh
The performance of a supercapattery depends on its energy density, rate capability of charge and discharge and stability of electrode. Here in, a sonochemical method followed by calcination was applied to synthesize nickel phosphate-silver phosphate (Ni3(PO4)2<img border="0" alt="single bond" src="https://cdn.els-cdn.com/sd/entities/sbnd">Ag3PO4) nanocomposites. Morphological studies revealed that crystalline Ag3PO4 (∼10 nm) was intimately anchored on the surface of amorphous Ni3(PO4)2, which benefits efficient charge transfer between the two metal phosphates. The optimized Ni3(PO4)2<img border="0" alt="single bond" src="https://cdn.els-cdn.com/sd/entities/sbnd">Ag3PO4 nanocomposite electrode exhibited a significant boost in rate capability from 29% (Ni3(PO4)2) to 78% capacity retention with the maximum specific capacity of 478C/g at 1 A/g in 1 M KOH electrolyte. The enhancement of rate capability originated from a more rapid electron-transfer rate and an augmentation of electroactive sites for electrolyte ion diffusion from the interfaces of porous Ni3(PO4)2 and an improvement in the electrical conductivity of crystalline Ag3PO4. The fabricated Ni3(PO4)2<img border="0" alt="single bond" src="https://cdn.els-cdn.com/sd/entities/sbnd">Ag3PO4//activated carbon-based supercapattery exhibited an energy density of 32.4 Wh/kg at 399.5 W/kg and excellent cyclic stability (∼82% capacity retention after 5000 cycles).
Self-supported cobalt nitride porous nanowire arrays as bifunctional electrocatalyst for overall water splitting Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Ziliang Xue, Jianyu Kang, Dong Guo, Chunling Zhu, Chunyan Li, Xitian Zhang, Yujin Chen
Designing noble-metal-free and highly active bifunctional electrocatalysts for overall water splitting is extremely desirable. Herein, we apply a facile method to fabricate cobalt nitride porous nanowires with a length of 7 μm and a diameter of 135 nm on carbon cloth (CC) as a bifunctional electrocatalyst for overall water splitting. The self-supported cobalt nitride porous nanowire arrays exhibit superior catalytic activities with a current density of 10 mA cm-2 at an overpotential of 97 mV for hydrogen evolution reaction and at an overpotential of 251 mV for oxygen evolution reaction. The alkaline water electrolyzer with the self-supported porous nanowire arrays as cathode and anode requires a cell voltage of 1.587 V to achieve a current density of 10 mA cm−2 and shows long-term stability at the high current density(∼360 mA cm−2) over 37 h, favorably comparable to the integrated performance of commercial Pt and IrO2.
Dynamics of single bubble departure from TiO2 nanorod-array photoelectrode Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Juanwen Chen, Liejin Guo, Xiaowei Hu, Zhenshan Cao, Yechun Wang
Bubble evolution from photo(electro)catalytic water splitting plays a vital role in the interfacial mass transport on photocatalyst surface. However, little success has been achieved to optimize this process, restricted by the poor understanding. Herein, taking photoelectrochemical (PEC) water splitting over a titanium dioxide (TiO2) nanorod-array electrode as a model system, experiments were performed to study single oxygen bubble dynamics by combining electrochemical measurement and high-speed microscopic imaging. The experimental results indicate that the departure of bubble from photoelectrode is retarded by light irradiation, but the traditional bubble departure criterions fail to predict the bubble departure diameters especially in high light intensity. Additional analysis reveals that the light irradiation causes the Marangoni force acting on the evolving bubble, because it induces temperature rise and generates dissolved gas. A modified force balance model for bubble departure from photoelectrode was developed by adding Marangoni force. This modified model that takes account of the light-induced temperature rise and the dissolved gas, agrees well with the experimental data and can be extended to other photo(electro)catalytic reactions.
Nature of mixed electrical transport in Ag2O-ZnO-P2O5 glasses containing WO3 and MoO3 Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 Luka Pavić, Ana Šantić, Juraj Nikolić, Petr Mošner, Ladislav Koudelka, Damir Pajić, Andrea Moguš-Milanković
This study reports on the nature of electrical transport and role of structural changes induced by different type and content of TMO in Ag-containing glasses of xTMO-(30-0.5x)Ag2O-(30-0.5x)ZnO 40P2O5 (TMO = MoO3/WO3, 0 ≤ x ≤ 60 mol%) composition. Raman spectra show clustering of WO6 units in glasses with high WO3 content while the addition of MoO3 induces a gradual change of MoO6 octahedra to MoO4 tetrahedra both being cross-linked with phosphate units without clustering. For WO3 glasses, minimum in DC conductivity is observed at 30–40 mol% of WO3 for temperatures from 303 to 513 K, followed by an increase in conductivity with further WO3 addition due to an increase in polaronic contribution. Observed turnover suggests a distinct transition from predominantly ionic to predominantly polaronic transport. Contrary, for MoO3 glasses conductivity decreases in the whole mixed compositional range indicating the nature of transport is dominated by ionic component throughout the measured temperature range. A comparative study of Ag+, Li+, Na+ transport in MoO3/WO3 glasses reveals a strong correlation between pre-exponential factor and activation energy, which allows detection of the prevalence of conduction mechanism. Finally, the results demonstrate that Ag2O WO3 ZnO P2O5 glass system is a promising electrically tunable material with significant contributions of ionic or polaronic conductivity depending on composition.
Electrochemical fabrication of 3D quasi-amorphous pompon-like Co-O and Co-Se hybrid films from choline chloride/urea deep eutectic solvent for efficient overall water splitting Electrochim. Acta (IF 4.798) Pub Date : 2018-04-09 W.Q. Yang, Y.X. Hua, Q.B. Zhang, H. Lei, C.Y. Xu
The development of earth-abundant, low-cost, highly active, and durable bifunctional catalysts competent for efficient electrochemical water-splitting is intensively demanding and of vital importance to realize high-purity hydrogen production. Herein, we report that 3D quasi-amorphous pompon-like Co-O and Co-Se hybrid films grown on copper foil (Co-O@Co-Se/Cu) can be electrochemically synthesized from a choline chloride and urea mixed deep eutectic solvent, denoted as Reline, via a facile one-step electrochemical deposition approach. Benefiting from the induction effect of Se, the obtained Co-O@Co-Se/Cu hybrid electrode exhibits strongly enhanced catalytic activity. The optimal Co-O@Co-Se/Cu sample shows good activity and excellent durability for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline solution with low overpotentials of 85 mV for HER and 340 mV for OER, respectively to reach a catalytic current of 10 mA cm−2. The Co-Se component within the hybrid films is gradually converted into Co-O species during the course of the OER, which are responsible for the good OER performance. In addition, when performed as bifunctional catalysts in a two-electrode configured electrolyzer, the Co-O@Co-Se/Cu couple displays a water-splitting current of 10 mA cm-2 at 1.65 V with reasonable stability for long-term electrolysis over 100 h. This simple one-step electrochemical synthesis route operated in the Reline-based deep eutectic solvent is demonstrated as an efficient strategy to fabricate active non-noble-free electrocatalysts toward overall water splitting applications.
A novel N,Fe-Decorated carbon nanotube/carbon nanosheet architecture for efficient CO2 reduction Electrochim. Acta (IF 4.798) Pub Date : 2018-04-07 Fuping Pan, Huilei Zhao, Wei Deng, Xuhui Feng, Ying Li
The development of high-performance electrocatalysts for CO2 reduction reaction (CO2RR) is a prerequisite to enable CO2-to-fuels electrolysis a feasible solution for reaching a carbon neutral cycle and producing value-added fuels. In this work, we report the design of a novel nanostructured electrocatalyst consisting of carbon nanotube/carbon nanosheet architecture with N and Fe doping (NFe-CNT/CNS) by a SiO2-protected calcination strategy. The hierarchical structure of CNT/CNS affords abundant N-induced defects and Fe−N species as highly active sites and facilitates mass transportation, and carbon nanotube also offers a smooth route for charge transfer in the CO2RR process. These synergistic merits afford NFe-CNT/CNS with high performance for CO2RR in terms of a maximum FE of 69% at a low overpotential of 0.48 V, a small Tafel slope of 89 mV dec−1, and enhanced stability for CO production in aqueous solution. The findings demonstrate that the integration of structural design and dopants optimization is effective to boost electrocatalytic activity of nanocarbons for CO2 reduction.
Polymer-assisted chemical solution synthesis of La0.8Sr0.2MnO3-based perovskite with A-site deficiency and cobalt-doping for bifunctional oxygen catalyst in alkaline media Electrochim. Acta (IF 4.798) Pub Date : 2018-04-07 Weichuan Xu, Litao Yan, Lara Teich, Steven Liaw, Meng Zhou, Hongmei Luo
The polymer-assisted chemical solution (PACS) method was used for the synthesis of La0.8Sr0.2MnO3 (LSM)-based perovskite catalyst network with nanoparticle size of 30–80 nm to enhance oxygen evolution reaction (OER) activity and maintain highly active oxygen reduction reaction (ORR). Samples investigated include the A-site cation deficient (La0.8Sr0.2)0.95MnO3-δ (ALSM) and the A-site cation deficient with the B-site cobalt-doped (La0.8Sr0.2)1-xMn1-xCoxO3-δ (x = 0.05 and 0.1 for LSMC5 and LSMC10, respectively). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) aided in physical characterizations. Electrochemical properties were tested in 0.1 M KOH solution by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Our results indicate as compared to LSM, the lattice-shrunk ALSM with high oxygen vacancy displays enhanced OER performance, but its inferior ORR activity could be caused by reduced crystallinity. LSMC5 and LSMC10 show lowest total overpotential (0.93 and 0.91 V vs. Ag/AgCl (3.5 M)) with slightly less efficient ORR, despite their superior specific kinetic current density. Oxygen vacancy induces Fermi level upshift and reduced resistivity, while Co-doping increases orbital hybridization and enhances charge transfer. Understanding how the A-site non-stoichiometry and the B-site doping influence the B<img border="0" alt="single bond" src="https://cdn.els-cdn.com/sd/entities/sbnd">O covalence is the key to the rational design of perovskite bifunctional oxygen catalysts.
Influences of trace water on electrochemical performances for lithium hexafluoro phosphate- and lithium Bis(oxalato)borate-based electrolytes Electrochim. Acta (IF 4.798) Pub Date : 2018-04-07 Xiaoling Cui, Fengjuan Tang, Yu Zhang, Chunlei Li, Dongni Zhao, Fangzhi Zhou, Shiyou Li, Huixia Feng
Water has a fatal influence on the performance of lithium ion batteries. In this work, Lithium hexafluoro phosphate(LiPF6)-ethylene carbonate (EC)/diethyl carbonate (DEC) and lithium bis(oxalato)borate (LiBOB)-tetramethylene sulfone (SL)/DEC are taken as examples to investigate the influences of water concentration for electrochemical window, acidity, impedance and cycling performance for lithium ion batteries by adjusting water concentrations in the electrolytes. Results show that LiBOB-based electrolyte has better water tolerance compared with LiPF6-based system, due to the formation of LiBOB·xH2O compounds by consuming the additive trace water. Besides, inductively coupled plasma test result shows that Mn ion dissolution in LiPF6 systems is extremely severe, which is mainly caused by the corrosive reaction between LiMn2O4 and by-product HF acid. And we believe that Mn ion dissolution and the following deposition should be responsible for failure work of LiPF6-based cells. But for LiBOB-based cells, stable SEI layers and good electrochemical performances have been obtained, benefitting from the synergistic effect between LiBOB salt and SL solvent. And the presence of high-resistance B(C2O4) (OH) and LiB(C2O4) (OH)2 products on surface of graphite electrode is the main reason for a small number of capacity fading.
Designing high-voltage and high-rate Li1-xNaxCoO2 by enlarging Li layer spacing Electrochim. Acta (IF 4.798) Pub Date : 2018-04-07 Qi Li, Kang Wu, Minmin Chen, Yu Lin Lee, Dongfeng Chen, Meimei Wu, Faqiang Li, Xiaoling Xiao, Zhongbo Hu
In our work, a series of Li1-xMxCoO2 (M = Na, x = 0–0.05) samples are synthesized by the solid-state calcination route. Electrochemical measurements show that high-rate capacities and high-voltage performances receive obvious improvements with an appropriate content of Na-doping. Specially, the capacity retention of Li0.97Na0.03CoO2 and LiCoO2 are 65.6% and 62.7% after the 100th cycles at 3.0–4.5 V, respectively. The discharge capacity of Li0.97Na0.03CoO2 compared with the pristine electrode LiCoO2 is greatly enhanced from 125 to 135 mAh·g−1 at the rate of 5C and 98 to 120 mAh·g−1 at the rate of 10C (1C = 140 mA g−1) respectively. With the larger radius of Na+ substituted for the smaller radius of Li+, it is found that the bond length of Li<img border="0" alt="single bond" src="https://cdn.els-cdn.com/sd/entities/sbnd">O is reduced from 2.0801 Å to 2.0781 Å, which is helpful for stabilizing the structure of LiCoO2 and improving the cycle capability at high voltages. At the same time, the inter-planar distance of Li slabs is expanded from 2.5904 Å to 2.59511 Å which can accelerate the diffusion of Li+ and improve the rate capacity. Therefore, Na-doped LiCoO2 shows outstanding high-voltage and high-rate performances, and the strategy can also be popularized and applied to other layered cathodes.
Preparation of nanoporous nickel-copper sulfide on carbon cloth for high-performance hybrid supercapacitors Electrochim. Acta (IF 4.798) Pub Date : 2018-04-07 Dongwei Du, Rong Lan, John Humphreys, Houari Amari, Shanwen Tao
In this work, nanoporous nickel-copper sulfide on carbon cloth was successfully prepared via sulfurizing the nickel-copper carbonate hydroxide precursor through an anion exchange reaction. The as-fabricated electrode exhibits a high specific capacitance of 938.6 F g−1 at a current density of 1 A g−1 and good rate capability of 76% at 10 A g−1, as well as excellent flexibility. Charge storage analysis demonstrates that the combination of surface-controlled capacitive process and diffusion-controlled Faradaic process, both contribute to the total capacitance. In addition, the good performance of the nanoporous nickel-copper sulfide can be attributed to the possible higher conductivity and porous nanostructures which offers more active sites to yield extrinsic pseudocapacitance. A hybrid supercapacitor was assembled with nickel-copper sulfide as the positive electrode and nitrogen-doped graphene as the negative electrode, delivering a high cell voltage up to 1.7 V with a maximum energy density of 35.3 Wh kg−1 and a maximum power density of 12700 W kg−1. The high performance we achieved suggests that the nanoporous nickel-copper sulfide has deep potential for high-performance supercapacitor applications.
Phenomenon of two transition times in chronopotentiometry of electrically inhomogeneous ion exchange membranes Electrochim. Acta (IF 4.798) Pub Date : 2018-04-07 D. Yu Butylskii, S.A. Mareev, N.D. Pismenskaya, P. Yu Apel, O.A. Polezhaeva, V.V. Nikonenko
Transition time in chronopotentiometry is an important parameter, which is widely used for electrochemical characterization of various systems. Occurrence of multiple transition times is typical for multicomponent or multilayer electrode and membrane systems. In this paper we show that there may be another cause of multiple transition times. It is electrical heterogeneity of ion exchange membrane surface. It is found that there are two transition times on the chronopotentiograms of a commercial anion-exchange MA-41 (Shchekinoazot) and two specially prepared cation-exchange heterogeneous membranes in dilute electrolyte solutions (0.02 M NaCl in the experiment). It is found that both transition times are determined by diffusion limitations of ion delivery to the membrane surface in the depleted diffusion layer. The value of the first transition time depends on the dimensions of the conductive regions and their surface fraction; this transition time is determined as the time necessary for the depletion of electrolyte concentration near the conductive regions of the surface. The rate of concentration depletion depends on the electromigration through the conductive regions, on the one hand, and on the normal the tangential ion diffusion to the conductive surface regions, which mitigate the concentration decrease, on the other hand. The experimental value of the first transition time for the laboratory-made membranes is in a good agreement with simulation using a 3D electrodiffusion model. The value of the second transition time is in a good agreement with the Sand theory, hence it is conditioned by the normal diffusion delivery of electrolyte from the solution bulk to the entire membrane surface. The tangential diffusion plays a secondary role in this stage of concentration polarization since current-induced convection levels off the concentrations along the heterogeneous membrane surface.
Polyvinyl alcohol protected Mo2C/Mo2N multicomponent electrocatalysts with controlled morphology for hydrogen evolution reaction in acid and alkaline medium Electrochim. Acta (IF 4.798) Pub Date : 2018-04-07 Xiaozhen Chen, Ji Qi, Pan Wang, Chuang Li, Chen Xiao, Changhai Liang
Herein, PVA-Mo2C/Mo2N nanospheres with surface roughness are synthesized via a polyvinyl alcohol (PVA) involved approach and used for hydrogen evolution reaction (HER). The average crystallite size of the PVA protected PVA-Mo2C/Mo2N nanospheres (6.1 nm) is one third of that of the PVA-Mo2C/Mo2N without PVA protection (17.9 nm). At 10 mA cm−2 current density, the as-synthesized PVA-Mo2C/Mo2N nanospheres with surface roughness exhibits HER overpotentials of 132 mV and 142 mV with corresponding Tafel slope of 51.8 mV dec−1 and 50.4 mV dec−1 in acid and alkaline medium, respectively. This high apparent activity can be attributed to the high intrinsic activity originated from the adjacent surface active sites of Mo2C and Mo2N as well as the large ECSA of PVA-Mo2C/Mo2N nanospheres with surface roughness.
Three-dimensional macrohomogeneous mathematical model of an industrial-scale high-temperature PEM fuel cell stack Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Monika Drakselová, Roman Kodým, Dalimil Šnita, Frank Beckmann, Karel Bouzek
Mathematical modelling offers an efficient tool for the development and optimization of various technologies, including fuel cells. However, the implementation and utilization of such a model for an industrial-scale fuel cell stack is a considerable challenge. The reason is that it consists of many layers and interphases which often display stiff behaviour. Consequently, a detailed mathematical model of such a stack is computationally difficult and highly demanding on the computational power of the hardware. The macrohomogeneous (volume-averaged) approach presented assumes a continuum on a characteristic length scale of a few centimetres (cumulative thickness of a few cells of the stack) in all spatial directions. The anisotropic structure of the real system is then expressed by means of anisotropic transport parameters. In this work, the macrohomogeneous approach is applied to a three-dimensional model of an industrial-scale high-temperature polymer electrolyte membrane (PEM) fuel cell stack consisting of 100 cells with two different flow-field geometries: (a) a 5-fold serpentine and (b) a parallel channel flow field. They were selected because of the significantly different uniformity of the gas distribution in the cell. Stationary conditions, dry pure hydrogen and air at the inlet, as well as common operating conditions (160 °C, 101.325 kPa) are considered. The model approach described not only helps to provide a better understanding of the behaviour of a fuel cell stack on a local scale, but also to identify potential weaknesses in the system design.
Fabrication of three-dimensional carbon coating for SnO2/TiO2 hybrid anode material of lithium-ion batteries Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Qinghua Tian, Jingbin Yan, Li Yang, Jizhang Chen
Charge storage mechanisms of birnessite-type MnO2 nanosheets in Na2SO4 electrolytes with different pH values: In situ electrochemical X-ray absorption spectroscopy investigation Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Chan Tanggarnjanavalukul, Nutthaphon Phattharasupakun, Juthaporn Wutthiprom, Pinit Kidkhunthod, Montree Sawangphruk
The charge storage mechanism of birnessite-type MnO2 nanosheet electrode with ca. 100 μm in thickness in 0.5 M Na2SO4 electrolytes with different pH values was investigated by an in situ electrochemical X-ray absorption spectroscopy (XAS) technique. It is found that the charge storage capacity of MnO2 is controlled by both surface adsorption and redox reaction. At pH 1 and 2, the rate of surface adsorption is faster than that of the surface redox reaction. Whilst, at pH 3, 4, and 5.9, the major capacitance originates from the redox reaction or the insertion/de-insertion of solvated cations into the layered MnO2 nanostructures. As a result, the MnO2-based supercapacitor electrode in 0.5 M Na2SO4 with diluted H2SO4 (pH 4) exhibits higher specific capacitance than that in electrolytes with pH 1–2. The decrease of capacitance at low pH is due to the partial dissolution of MnO2. This finding may lead to better understanding on the charge storage mechanism of the MnO2 materials.
Electrochemical energy storage of nanocrystalline vanadium oxide thin films prepared from various plating solutions for supercapacitors Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Jian-De Xie, Hui-Ying Li, Tzi-Yi Wu, Jeng-Kuei Chang, Yasser Ashraf Gandomi
Nanocrystalline V2O5 is electrochemically deposited onto an indium tin oxide substrate in VOSO4–based solution with various acetate additives, i.e., lithium acetate, sodium acetate, and potassium acetate. The deposition conditions including pH value and acetate additive are found to be crucial factors in influencing the deposition rate, crystallinity, and porous structure of V2O5 electrodes. The electrochemical capacitive behavior of the deposited V2O5 electrodes in KCl electrolyte is investigated by cyclic voltammetry at various scan rates, ranged from 5 to 200 mV s−1. The specific capacitance of V2O5 electrode prepared from the potassium acetate containing plating solution is up to 350 F g−1, indicating that the level of K+ occupancy reaches as high as 0.71. This suggests that the occupancy of K+ ions is in tetrahedral and eight coordinated sites in V2O5 crystals. The capacitance retention at 200 mV s−1 compared to that at 5 mV s−1 reaches to 75% for this electrode. The enhanced performance is mainly attributed to the highly porous structure which significantly increases the active sites, imparts oxide/electrolyte interfaces for energy storage, and subsequently enhances the rate of insertion/extraction of K+ ions. The V2O5 electrode is capable of delivering high energy density up to 48.6 Wh kg−1, demonstrating a significant potential for thin-film energy storage devices.
Reduced graphene-oxide/highly ordered mesoporous SiOx hybrid material as an anode material for lithium ion batteries Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Dan Liu, Congrui Chen, Yanyan Hu, Jorryn Wu, Dong Zheng, Zhi-zhong Xie, Gongwei Wang, Deyang Qu, Junsheng Li, Deyu Qu
rGO wrapped SiOx with ordered meso-porous structure material is fabricated via a facile route. This meso-porous SiOx/rGO composite, used as anode in LIBs, exhibits a reversible capacity of 580 mAh g−1 under the applied current density of 100 mAg−1 up to 200 cycles. And it still can deliver a reversible capacity of 120 mAh g−1 even at 10,000 mA g−1 rate. The high cyclic stability and superior rate performance is attributed to the graphene layer as well as the inert products formed in the reduction of SiOx, which can buffer the volume expansion elastically, thus preserve the integrity of the electrode. Moreover, the ordered meso-porous structure can provide high specific surface area, sufficient void space to shorten the pathway of Li ions, improve the electrolyte penetration and enhanced the electrochemical Li ion storage.
Influence of dipping cycle on SILAR synthesized NiO thin film for improved electrochemical performance Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Mahima Ranjan Das, Atanu Roy, Siyasanga Mpelane, Ayan Mukherjee, Partha Mitra, Sachindranath Das
NiO thin films have been successfully synthesized using by successive ionic layer absorption and reaction (SILAR) technique which is simple, cost-effective and low-temperature wet chemical process. Influences of deposition cycle on structural and morphological property were investigated using XRD and FESEM. Surface morphological study shows formation of highly porous network which provides more active sites and deposition path for electrolyte ions. NiO thin film based electrode provides highest specific capacitance of 1341 Fg−1 at the voltage scan rate of 2 mVs−1 for the film deposited at 40 deposition cycle. From charging -discharging curve of NiO electrode, specific capacitance value of 877 Fg−1 at current 1 Ag−1for the film deposited at 40 deposition cycle was observed. It shows highest specific energy of 64.8 Wh Kg−1. The NiO electrode exhibited long-term cycle stability with 90% capacitance retention after 1000 cycle. Such attractive electrochemical performance of the formed electrode is suitable for the manufacturing of the good quality supercapacitors for commercial application.
Stable boron nitride nanocomposites based membranes for high-efficiency proton conduction Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Wei Jia, Peiyi Wu
Proton conduction is a not only a universal and fundamental process in nature but also have been widely used in energy- and environment-related applications. Achieving high-efficiency proton conduction is very important in these areas. Herein, stable and selective membranes with novel ionic nanochannels based on functionalized two-dimensional boron nitride nanocomposites (NBN) are successfully fabricated. The proton conductivity of Nafion-sNBNM at 80 °C - 95 %RH is as high as 0.44 S cm−1. At the same time, NBN-sNBNM shows impressing stability at high-humidity conditions and in redox environments. The high proton conductivity could be attributed to the favorable microphysical and microchemical environments of the nanochannels in the membranes. On one side, the double-layer space among the closely assembled NBN propels the local surface-charge enhanced proton conduction. On the other side, the formation of connected long-range ionic nanochannels and quasi-isotropic architecture facilitate the long-range proton conduction. Benefiting from the excellent stability of NBN, the proton conductivity of Nafion-sNBNM at high-temperature and low-humidity conditions could be conveniently increased by H3PO4 adsorption. Furthermore, Nafion-sNBNM also shows low methanol permeability and high membrane selectivity. These outstanding properties of Nafion-sNBNM demonstrate great application potential in many areas.
Effect of air pressure on the electro-Fenton process at carbon felt electrodes Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 J.F. Perez, S. Sabatino, A. Galia, M.A. Rodrigo, J. Llanos, C. Sáez, O. Scialdone
The effect of air pressure on electro-Fenton (PrEF process) was evaluated using two organic substances (maleic acid and Acid Orange 7) as model organic pollutants. First experiments were performed using a conventional carbon felt (CF) cathode. At room pressure, a slow removal of maleic acid was obtained, together with the generation of formic acid. Conversely, using pressurized air, the removal of maleic acid was dramatically accelerated and the formation of formic acid was not detected. The utilization of a carbon felt modified by the deposition of carbon black + PTFE mixture (MCF) and of pressurized air allowed to achieve even faster and almost total (>95%) removal of total organic carbon (TOC). Interestingly, the abatement resulted higher than the one obtained previously by direct anodic oxidation at boron doped diamond under comparable conditions. Similarly, in the case of Acid Orange 7 (AO7) the removal of the TOC increased with the pressure using both CF and the MCF. In particular, high removal of TOC (close to 80%) was obtained using the MCF at high current density (100 mA cm−2) under pressurized air.
Coral-like Cu-Co-mixed oxide for stable electro-properties of glucose determination Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Rui-mei Yuan, He-jun Li, Xue-min Yin, Jin-hua Lu, Lei-lei Zhang
Nanowire-constructed coral-like spinel Cu-Co-mixed oxides were synthesized via hydrothermal reaction. Owing to the unique nanoarchitecture, the Cu-Co-O provide abundant electro-active sites and channels for ions transfer. And also because of the synergistic effect of copper and cobalt ions in the spinel crystal, the electrode modified with the Cu-Co-O material shows prominent electrocatalytic performance toward the oxidation of glucose. The rapid amperometric response to glucose was observed with a high sensitivity (8838.26 μA cm-2 mM-1), low detection limit (0.5 μmol/L) and fast response (within 1 s). The mild synthesis method and outstanding electrocatalytic performance make it promising for the reliable and durable determination of glucose.
Pony-size Cu nanoparticles confined in N-doped mesoporous carbon by chemical vapor deposition for efficient oxygen electroreduction Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Yangyang Ni, Zhengyan Chen, Fantao Kong, Yu Qiao, Aiguo Kong, Yongkui Shan
The pony-size Cu nanoparticles confined in mesoporous C-N were directly synthesized by chemical vapor deposition (CVD) method using floating Cu atoms. The mesoporous C-N with high surface area not only stabilized the dispersed Cu nanoparticles but also improved the electrocatalytic activity of the Cu by changing the electronic structure of Cu. Combining the strong interaction between Cu nanoparticles and mesoporous C-N and the quantum size effect of Cu nanoparticles, the obtained Cu@C-N exhibited the catalytic activity superior to the reported Cu nanoparticles-based catalysts and commercial Pt/C-JM catalyst with a half-wave potential of 0.84 V for oxygen reduction reaction (ORR) in alkaline media. Additionally, it also showed remarkable catalytic stability and excellent methanol-tolerant property during the ORR process.
A base-stable metal-organic framework for sensitive and non-enzymatic electrochemical detection of hydrogen peroxide Electrochim. Acta (IF 4.798) Pub Date : 2018-04-06 Nasrin Siraj Lopa, Md Mahbubur Rahman, Faiz Ahmed, Sabuj Chandra Sutradhar, Taewook Ryu, Whangi Kim
Stability of metal-organic frameworks (MOFs) in aqueous medium and extreme solution conditions (acidic or basic) are important for the development of stable, reproducible, and sensitive electrochemical biosensors. Herein, a base-stable chromium(III) dicarboxylate MOF was synthesized by microwave assisted solvothermal method for non-enzymatic detection of hydrogen peroxide (H2O2). The as-synthesized MOF exhibited excellent base stability without any obvious changes in crystallinity, morphology, and spectroscopic behaviors after base treatment. This MOF-modified glassy carbon electrode showed negligible change in charge transfer resistance at the electrode|electrolyte interface after redox cycling and good catalytic activity for the reduction of H2O2 in 0.1 M NaOH(aq.). The enhanced catalytic activity of H2O2 reduction is enabled by the redox process of CrIII/II in the chromium (III) dicarboxylate. The sensor showed the sensitivity of ca. 11.9 μA mM−1, wide linear range from 25 to 500 μM, and a method detection limit of ca. 3.52 μM. The validation of this sensing platform was evaluated by standard addition method. Thus, the present biosensor could be used for the point of care detection of H2O2.
Nanostructured copper–cobalt based spinel for the electrocatalytic H2O2 reduction reaction Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Narayan Chandra Deb Nath, Trishna Debnath, Eun-Kyung Kim, Md Aftab Ali Shaikh, Jae-Joon Lee
Nanostructured copper–cobalt based spinel [(Cu0.30Co0.70)Co2O4] was employed as an electrocatalyst in the hydrogen peroxide (H2O2) reduction reaction (HRR). Both nanoparticles and nanoneedles co-existed in the (Cu0.30Co0.70)Co2O4 spinel, which exhibited a high intrinsic electrical conductivity and surface-to-volume ratio, resulting therefore in a large electrochemically active surface area for the HRR. In addition, (Cu0.30Co0.70)Co2O4 showed an onset potential at approximately −0.14 V in the HRR, with a limiting current density of ∼104 mA/cm2 at −0.43 V. The synthesised material followed the direct HRR pathway and exhibited good stability. In addition, the HRR activity of (Cu0.30Co0.70)Co2O4 was comparable to that of commercial Pt/C electrodes. The present results therefore demonstrate the significant potential of (Cu0.30Co0.70)Co2O4 for future applications in fuel cells as a cathode catalyst.
Detection of under deposit corrosion in CO2 environment by electrochemical noise and recurrence quantification analysis Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Y. Hou, C. Aldrich, K. Lepkova, B. Kinsella
In this study, the corrosion of carbon steel immersed in CO2 saturated aqueous solutions, in the presence and absence of sand deposits, were investigated by electrochemical noise measurement and recurrence quantification analysis. Uniform corrosion occurred at samples without sand deposit while localized corrosion took place at the sand-covered steel samples. These two different corrosion types can be accurately predicted by random forest and principal component models based on recurrence quantification analysis of either electrochemical potential or current noise data regardless of threshold values. The study provides a potential automated online corrosion monitoring scheme to ensure the integrity of pipelines.
Enhanced electrochemical sensitivity towards acetaminophen determination using electroactive self-assembled ferrocene derivative polymer nanospheres with multi-walled carbon nanotubes Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Yuan Chen, Xiaoying Liu, Tengteng Wu, Wenli Hou, Meiling Liu, Youyu Zhang, Shouzhuo Yao
Electron mediators have the ability to facilitate electron acceptance and donation, which can accelerate the electron transfer during the electrochemical process. Few research has been reported about electroactive polymer nanospheres as redox mediators for sensing to date. In this study, we synthesized a new electroactive ferrocene derivative polymer nanospheres (FPS) via a facile and self-assembly method. The obtained FPS was characterized by UV–Vis spectra, Fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. Based on the electroactive property of FPS, a new electrochemical sensor for acetaminophen (AP) based on the nanocomposite of multi-walled carbon nanotubes-ploy-diallyl-dimethyl-ammonium chloride-FPS (MWCNT- PDDA-FPS) was firstly developed. The greatly enhanced electrochemical performance towards AP determination can be obtained owing to the electrocatalysis of electroactive FPS and good conductivity of MWCNT. The AP sensor exhibits a wide sensing linear range from 3 to 1100 μM and the detection limit is 0.6 μM (S/N = 3). Therefore, these ferrocene derivative polymer nanospheres may become a new nanomaterial to construct of platforms for bioanalytical and electrochemical immune research in the future.
Fabrication of PANI-coated ZnFe2O4 nanofibers with enhanced electrochemical performance for energy storage Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Hui Qiao, Rongrong Li, Yuting Yu, Zhaokang Xia, Lijun Wang, Qufu Wei, Ke Chen, Qiquan Qiao
We successfully combined electrospinning with in situ polymerization methods to synthesize the PANI-coated ZnFe2O4 nanofibers which possess the abundant pore structure. The lithium storage properties of PANI-coated ZnFe2O4 nanofibers as anode materials for lithium-ion batteries have been discussed for the first time. PANI nanoparticles were directly coated on the surface of the ZnFe2O4 nanofibers, increasing the electrical conductivity, and also acting as the protect shell to enhance the mechanical strength of material. The electrochemical performance showed that 15% PANI incorporated ZnFe2O4 composite nanofibers (ZP-15) exhibited the highest reversible capacity of 1142 mAhg−1 after 50 cycles, which was much higher than that of pure ZnFe2O4 nanofibers (628 mAhg−1), 10% PANI incorporated ZnFe2O4 composite nanofibers (ZP-10, 975 mAhg−1), and 20% PANI incorporated ZnFe2O4 composite nanofibers (ZP-20, 536 mAhg−1). Additionally, the ZP-15 composite nanofibers achieved outstanding cycling rate capacity of 852, 738, 609 and 539 mAhg−1 with current densities range from 500 to 5000 mA g−1, and exhibited a specific capacity of 1082 mAhg−1 when the current reverted to 50 mA g−1 from the high rate charge-discharge cycles. The enhanced electrochemical performance of PANI-coated ZnFe2O4 nanofibers can be attributed to the PANI providing a highly electrical conductive medium, which can promote electron transfer and facilitate the Li+ transport in the lithiation/delithiation process, also can reduce self-discharge; moreover, the PANI layer covered on the surface of ZnFe2O4 nanofibers can be as buffer matrix to restrain the stress of volume expansion to get stable structure.
Tuning of physical and electrochemical properties of nanocrystalline tungsten oxide through ultraviolet photoactivation Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 P.T.G. Gayathri, S. Sajitha, I. Vijitha, S.S. Shaiju, R. Remya, Biswapriya Deb
In this paper, we demonstrate the use of ultraviolet (UV, 365 nm) photoactivation to induce functional changes in the nanocrystalline tungsten oxide (n-WO3) surfaces. n-WO3 was initially synthesized by dissolving hydrated-WO3 powder in 10% H2O2 with and without UV exposure. The photoactivation triggered homogeneous ligand-stripping in WO3 seeds that transformed the random-shaped clusters observed in the unexposed solution into a mono-modal distribution of spherical aggregates. These aggregates were electrophoretically collected as a coating that exposed to a second installment of UV soaking to explore photoactivation effects in the film state. A significant network densification is observed as photo-decomposition of bridging ligands facilitated direct interactions of surface dipoles in those films. Experiments showed that the photodecomposition mechanism predominantly depends upon the discharge of oxygen atoms localized on the material surface that can also create donor type oxygen vacancies. Electrochemical studies showed that the photoactivation led up to ∼2.8✕ enhancement in the surface donor density and considerably improved the interfacial charge transfer. The photoactivated electrodes exhibited up to ∼33% increment in the areal capacitance (Ca) due to the increased number of active sites in the interface. Electrochromic (EC) response from the same electrodes produced ∼57% improvement in the optical density (OD).
Excellent electrochemical performance of graphene oxide based strontium sulfide nanorods for supercapacitor applications Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Muhammad Faisal Iqbal, Muhammad Naeem Ashiq, Aamir Razaq, Ghulam Murtza, Bushra Parven, Mahmood-Ul Hassan
Owing to large specific surface area and high electrical conductivity, nanostructured electrodes exhibit improved electrochemical activity for supercapacitor applications. In the present study, structure and morphology of hydrothermally synthesized strontium sulfide and graphene oxide based Strontium sulfide nanorods has been investigated by using XRD and SEM, respectively. Introduction of graphene oxide thin film improves specific surface area and resulting in the excellent electrical conductivity of Strontium sulfide nanorods. Due to this, graphene oxide based strontium sulfide nanorods illustrate excellent specific capacitance and energy density of 1831.14 F g−1 and 91.56 WhKg−1, respectively, at the current density of 3 mAcm−2, as measured by employing three electrode galvanostatic charge discharge system. Moreover, electrode of graphene oxide based strontium sulfide nanorods also shows good electrochemical performance, according to the measurements by symmetric two electrode system. Energy and power density is measured as 10.55 WhKg−1 and 294.35 W kg−1, respectively. The excellent electrochemical performance of graphene oxide based strontium sulfide nanorods reveals its significance as nanostructured materials for supercapacitor applications.
One-step fabrication of in situ carbon-coated NiCo2O4@C bilayered hybrid nanostructural arrays as free-standing anode for high-performance lithium-ion batteries Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Yu Wang, Pengcheng Liu, Kongjun Zhu, Jing Wang, Kang Yan, Jinsong Liu
Rapid developments in revolutionary electric vehicles have led to an increase in the energy-density and cycling-life requirements for Li-ion batteries (LIBs). The binary transition metal oxide NiCo2O4 is attracting considerable attention due to its much larger specific capacity than graphite. However, NiCo2O4 suffers from poor cycling performance owing to a large volume change during cycling. To address this problem, we proposed an easy strategy to fabricate in situ carbon-coated NiCo2O4 bilayered hybrid nanostructural arrays supported on Ni foam (denoted as NiCo2O4@C BHNAs–NF) as free-standing anodes for LIBs through a sucrose-assisted hydrothermal method. The in situ-synthesized uniform carbon shell can simultaneously buffer the volume change during cycling and increase the conductivity. The micro/nano-structure also possessed outstanding structural advantages, such as large surface area and hierarchical porous characters, enabling NiCo2O4@C BHNAs–NF to have excellent electrochemical performance. Its capacity can reach 1298 mAh/g at a current density of 100 mA/g, and 86% of the initial capacity can be retained after 100 cycles. All these results revealed that NiCo2O4@C BHNAs–NF was a promising candidate anode for next-generation LIBs.
Low temperature preparation of pore structure controllable graphene for high volumetric performance supercapacitors Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Songbo Chen, Wensheng Gao, Yuanzhi Chao, Yu Ma, Yunhai Zhang, Nan Ren, Huqiang Chen, Lijun Jin, Jiangong Li, Yongxiao Bai
High volumetric capacitance of supercapacitor is important and challenging for practical application in the energy storage devices. Herein, we develop a simple and effective approach to fabricate functionalized and pore structure controllable graphene via low temperature (∼170 °C) thermal treatment of graphite oxide with designed particle size. The as-obtained graphene with oxygen contents of 14.19 at.%, porous structure and a relative low pore volume (0.38 g cm−3), exhibits a promising material for the application in high volumetric performance supercapacitors. The prepared supercapacitor delivers a high volumetric capacitance of 226.9 F cm-3 at 0.5 A g−1 and achieves high rate capability (79% capacitance retention at 20 A g−1) in alkaline electrolyte. Moreover, the assembled supercapacitor in neutral electrolyte also exhibits a high volumetric energy density of 15.1 Wh L−1 as well as a high cycling stability with 94.2% retention after 9000 cycles. Therefore, this work will provide a new strategy for designing high volumetric capacitive performance of graphene for energy storage devices.
A bipotentiostat based separation-free method for simultaneous flow injection analysis of chromium (III) and (VI) species Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Subramanian Nellaiappan, Annamalai Senthil Kumar
Chromium(III) species is an essential micronutrient, whereas, its hexavalent form, Cr(VI) is considered to be a carcinogen. For the selective detection of Cr(III) in presence of Cr(VI), separation coupled spectroscopic techniques have been often used. For the first time in this work, we report a flow injection analysis coupled dual electrochemical detector (FIA-DECD) for separation-free detection of Chromium (III) and (VI) species. A gold nanoparticles decorated carbon nanofibres-chitosan modified electrode has been prepared by a quick and in-situ electrochemical deposition of Au3+ ion in pH 7 phosphate buffer solution (PBS) and has been used as a dual electrochemical detector for Cr(VI)-reduction and Cr(III)-oxidation reactions in pH 2 PBS. Under an optimal hydrodynamic FIA-DECD condition, i.e., at applied potentials 0.1 V (for Cr(VI)-reduction) and 1 V vs Ag/AgCl (for Cr(III)-oxidation) and at a flow rate = 0.8 mL min−1, calculated linear range and detection limit values are; 0.1–100 ppm and 0.69 ppb (0.72 ppt for 20 μL sample loop volume) for Cr(III) and 0.1–100 ppm with detection limit, 0.32 ppb (0.33 ppt for 20 μL) for Cr(VI). No marked interference from other cations and anions like Cu2+, Zn2+, Cd2+, Pb2+, Co2+, Ca2+, Fe2+, Mg2+, NO3−, NO2−, SO32− and SO42− were noticed. Selective detection of Cr species (Cr(III) and Cr(VI)) in industrial waste water samples with data comparable to ICP-OES was demonstrated.
Confining small sulfur molecules in peanut shell-derived microporous graphitic carbon for advanced lithium sulfur battery Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Jingjing Zhou, Yongsheng Guo, Chengdu Liang, Jun Yang, Jiulin Wang, Yanna Nuli
In this work, small sulfur molecules (S2-4) confined in microporous graphitic carbon (MGC) demonstrates excellent performance in Li-S battery with carbonate-based electrolyte. The MGC is synthesized via the simultaneous activation and graphitization of peanut shell char promoted by K2FeO4, which possesses ultra-micropore (pore width <0.7 nm) volume as high as 0.65 cm3 g−1 and the predominant pore width less than 0.4 nm. After sulfur infusion, the S/MGC composite with 50.5 wt% sulfur loading exhibits superior long-term cycling stability and rate performance in S/MGC | Li full cell. The cell delivers high capacity of 1146 mAh g−1 at 0.1 C and 570 mAh g−1 even at 4 C. Moreover, the capacities of 826 and 571 mAh g−1 remain after 1000 cycles at 1 C and 2 C, respectively. In addition, the cell exhibits good storage property. The well confined S2-4 inside the interconnected ultra-micropores with graphitic carbon walls endows the S/MGC composite with good electronic conductivity and stability, while un-occupied pores within the S/MGC facilitate fast Li+ transport and kinetics of electrochemical reactions. This work offers a green and sustainable route to promote the application of Li-S batteries.
Hollow ZIFs-derived nanoporous carbon for efficient capacitive deionization Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Jiaming Shen, Yang Li, Chaohai Wang, Rui luo, Jiansheng Li, Xiuyun Sun, Jinyou Shen, Weiqing Han, Lianjun Wang
Desalination performance of capacitive deionization (CDI), a promising deionization technology, depends significantly upon the compositions and internal structures of electrode materials. Herein, hollow ZIFs-derived nanoporous carbons (HZCs) were prepared via chemical etching method and subsequent pyrolysis. Particularly, the tannic acid as an etching agent was employed to tailor hollow structure. The resultant HZCs possess high surface area, wide pore size distribution, obvious hollow cavity and high nitrogen content. Moreover, HZCs electrodes exhibited a significantly improved CDI performance over the solid ZIF-derived nanoporous carbons (SZCs) electrodes. The improved electrosorption rate and capacity (15.31 mg g-1 at 1.2 V) of HZCs electrode imply that hollow structure facilitates the transportation for both ions and mass on CDI process. Besides, the further cycle experiment exhibits a great regeneration stability of HZCs electrode over 20 adsorption-desorption cycles. All these results indicate that HZCs should be a promising candidate for CDI application.
Effect of different contents of organic-inorganic hybrid particles poly(methyl methacrylate) ZrO2 on the properties of poly(vinylidene fluoride-hexafluoroprolene)-based composite gel polymer electrolytes Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Zhiyan Wang, Chang Miao, Wei Xiao, Yan Zhang, Ping Mei, Xuemin Yan, Yu Jiang, Minglei Tian
Poly(vinylidene fluoride-hexafluoroprolene) (P(VDF-HFP))-based composite polymer electrolyte (CPE) membranes doped with organic-inorganic hybrid particles poly(methyl methacrylate) ZrO2 (PMMA-ZrO2) are fabricated by phase inversion, in which PMMA is firstly successfully grafted onto the surface of the homemade nano-ZrO2 particles via in situ polymerization confirmed by FT-IR. XRD and DSC patterns show that adding PMMA-ZrO2 into the polymer matrix can decrease the crystallinity of the CPE membranes and TG curves indicate the CPE membranes possess desirable thermal stability. It can be found that the CPE membrane presents a uniform surface with abundant interconnected micro-pores when the added amount of PMMA-ZrO2 increases to 5 wt % vs. polymer matrix, in which the ionic conductivity at room temperature and tensile strength can be up to 3.595 mS cm−1 and 26.18 MPa, respectively. In particular, the CPE membrane shows the minimum deformation of about 8% after being exposed at 160 °C for 1 h, and the electrochemical working window of the assembled Li/CPE/SS cell can be stable at 5.1 V (vs Li/Li+) at room temperature. Moreover, the LiCoO2/CPE/Li coin cell can deliver a specific capacity of 114.5 mAh g−1 with 79.13% capacity retention at 2.0 C after 110 cycles. The results suggest that the as-fabricated P(VDF-HFP)-based CPE doped with 5 wt % organic-inorganic hybrid particles PMMA-ZrO2 can be a promising polymer electrolyte for lithium ion batteries.
Ultrasensitively photoelectronchemical determination of cysteine and coenzyme A with CdSe quantum dots-covered ZnO nanorods photoelectrode Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Changzhi Zhao, Yanyun Kong, Licheng Liu, Xiaoyu Wang
A new photoelectrochemical system was fabricated by incorporating the cysteine or coenzyme A as electron donor into photoelectrochemical reaction of the nanostructured CdSe/ZnO photoelectrode to develop a photoelectrochemical method for the ultrasensitive determination of the cysteine and coenzyme A. The CdSe/ZnO photoelectrode was prepared by covering the CdSe quantum dots on the surface of ZnO nanorods arrays. The property of photoelectrode was investigated as photosensitive interface and electron acceptor, and its photoelectrochemical reaction was study with substrate. Under the 20 mW/cm2 410 nm visible light illuminations, the sensitive photocurrent response to the cysteine or coenzyme A was obtained at bias voltage 0 V. After the optimized experimental conditions, the photocurrent was proportional to the concentration of cysteine or the logarithm of coenzyme A concentration in the range of 1.00 × 10−2–20.0 μmol/L and 2.00 × 10−2–50.0 μmol/L, respectively. The detection sensitivity was 71.7 nA/μmol/L for cysteine. The detection limit was estimated to be 6.00 × 10−3 μmol/L (S/N = 3) and 1.00 × 10−2 μmol/L (S/N = 3) for cysteine and coenzyme A, respectively. The other amino acids or common coenzymes were not interfering with the determination of cysteine and coenzyme A. Compared with other methods for the determination of cysteine and coenzyme A, the proposed method exhibits a wide measurement range, high sensitivity, and low cost.
Hollow graphene-polyaniline hybrid spheres using sulfonated graphene as Pickering stabilizer for high performance supercapacitors Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Jing Luo, Yaxin Chen, Yuan Zheng, Chenbeibei Wang, Wei Wei, Xiaoya Liu
Hollow structured graphene-polyaniline spheres (GSA/PANI HS) were prepared via a facile and efficient Pickering emulsion polymerization using sulfonated graphene (GSA) as Pickering stabilizer. In our procedure, amphiphilic sulfonated graphene (GSA) was first synthesized and used to stabilize an oil phase containing aniline. Upon aniline polymerization at the oil/water interface, graphene-polyaniline hollow sphere (GSA/PANI HS) with a rough outer surface and a smooth inner surface, was generated. The size as well as the electrochemical properties of GSA/PANI HS could be easily adjusted by varying the amphipathicity and concentration of GSA, and the oil-water volume ratios of the Pickering emulsions. The synthesized GSA/PANI HS exhibited superior performance in supercapacitors compared to the common stacked two-dimensional GSA/PANI composite owing to its unique hollow structure, which provides a larger accessible surface area and reduces the transport length for both charge and ion The specific capacitance of GSA/PANI HS can reach 546 F g−1, more than two folds higher than stacked two-dimensional GSA/PANI composite. In addition, GSA/PANI HS reveals enhanced capacitance retention at higher scan rates (76% from 5 to 500 mV s−1) and current densities (83.5% from 0.5 to 10 A g−1), demonstrating superior electrochemical accessibility of the 3D hollow nanostructure. Furthermore, good cycling stability is also demonstrated, which render them interesting candidates for future electrochemical energy storage systems. This approach represents a simple, convenient and controllable route for the preparation of hollow graphene-polyanline nanostructures for high performance supercapacitor applications.
Tuning the component ratio and corresponding sodium storage properties of layer-tunnel hybrid Na0.6Mn1-xNixO2 cathode by a simple cationic Ni2+ doping strategy Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Hui Chen, Zhenguo Wu, Zhuo Zheng, Tingru Chen, Xiaodong Guo, Juntao Li, Benhe Zhong
Manganese (Mn)-based cathodes with advantages of low-cost, environmental benign, high energy density are crucial for the commercial process of sodium ion batteries (SIBs). Layer-tunnel hybrid cathode, which aims to integrate high capacity of P2-type layered structure with excellent cycling stability, superior rate performance of tunnel structure, deserves great research efforts. To further enhance the respective performance, the ratio of layer-tunnel component in the hybrid Na0.6Mn1-xNixO2 was adjusted by a simple cationic Ni2+ doping route. The crystal structure and electrochemical behavior of Na0.6Mn1-xNixO2 were carefully detected, compared and analyzed. The comprehensive results evidenced that the layered component ratio would rapidly increase with Ni2+ doping. The structural parameters of pure phase would also be affected by varied Ni2+ content. And 5% Ni doping could be an optimized point in terms of reversible capacity, cycling stability, rate performance and reaction kinetics. This study would reveal the dual-function of cationic doping in both macro scale component ratio and atomic scale crystal lattice parameter, and grasp new insight into the design and optimization of high performance hybrid cathode for SIBs.
NiCoSe2-x/N-doped C mushroom-like core/shell nanorods on N-doped carbon fiber for efficiently electrocatalyzed overall water splitting Electrochim. Acta (IF 4.798) Pub Date : 2018-04-05 Jiang Li, Meng Wan, Tao Li, Han Zhu, Zhenghuan Zhao, Zheng Wang, Weiwei Wu, Mingliang Du
Developing stable and efficient bifunctional catalysts for overall water splitting is a critical step in the production of renewable energy sources. Here we report a stable and highly active electrocatalyst comprised of NiCoSe2-x/N-doped carbon mushroom-like core/shell nanorods on silk-derived carbon fiber through one step selenization. The unique one-dimensional nanorod structure facilitates the charge transport, and the N-doped carbon shell also increases the electrical conductivity, resulting in a remarkable enhancement of the catalytic activity. The N-doped carbon shell also functions as a protection layer. The composite catalyst therefore exhibits outstanding OER and HER performance, it can also stably drive the overall water splitting at a low cell voltage of 1.53 V in base solution. The present work provides an efficient strategy for the fabrication of stable and active electrocatalysts with earth-abundant elements.
Interface-rich core-shell ammonium nickel cobalt phosphate for high-performance aqueous hybrid energy storage device without a depressed power density Electrochim. Acta (IF 4.798) Pub Date : 2018-04-04 Miao Wang, Yueping Zhao, Xuejiao Zhang, Ruijuan Qi, Shanshan Shi, Zhiping Li, Qingjie Wang, Yufeng Zhao
Introducing diffusion-controlled battery materials to supercapacitors, can significantly enhance the energy density of supercapacitors, which however encounter depressed power density due to the intrinsic sluggish charge storage kinetics of battery materials. This problem can be efficiently solved by modifying the microstructure, and enable capacitive controlled charge storage mechanism in the battery materials. In this work, a novel interface-rich core-shell structure with (NH4)(Ni,Co)PO4·0.67 H2O nanosheets @ single crystal microplatelets (NH4)(Ni,Co)PO4·0.67 H2O (NCoNiP@NCoNiP) is constructed via a facile two-step hydrothermal method, taking advantage of etching induced Kirkendall effect and Ostwald ripening. This unique structure can enable the extrinsic pseudocapacitance by providing extra charges (e.g. holes, electrons or voids) on the interfaces, and realize synergy and fast charge storage. Specifically, a maximum specific capacity of 190.3 mAh g−1 and ultrahigh rate performance with capacity retention of 96.1% from 1 to 10 A g−1 in a three-electrode test. The kinetic analysis indicates that the electrochemical response of the hybrid battery-supercapacitor storage devices shows obvious characteristic of supercapacitor especially at high scanning rates. Simultaneously, the hybrid battery-capacitor devices based on NCoNiP@NCoNiP exhibits a high energy density of 44.5 Wh kg−1 at a power density of 150 W kg−1, which maintains 30 Wh kg−1 at high power density of 7.4 kW kg−1 with capacitance retention 77.5% after 7000 cycles. This work provides a novel strategy for the application of battery materials in high power devices, by enabling the capacitive charge storage mechanism of battery materials through nanostructure engineering.
A phenylenediamine-mediated organic electrolyte for high performance graphene-hydrogel based supercapacitors Electrochim. Acta (IF 4.798) Pub Date : 2018-04-04 Jianhui Fang, Xiangxin Zhang, Xiaofei Miao, Yongchuan Liu, Sujing Chen, Yuanqiang Chen, Jian Cheng, Wei Wang, Yining Zhang
Lithiation heterogeneities of graphite according to C-rate and mass-loading: A model study Electrochim. Acta (IF 4.798) Pub Date : 2018-04-03 Nicolas Dufour, Marion Chandesris, Sylvie Geniès, Mikaël Cugnet, Yann Bultel
Performance and durability of lithium-ion batteries highly rely on local conditions inside electrodes during operation. In this paper, local physical conditions inside a standard graphite electrode are explored at various C-rate and mass-loading with a physic-based model, validated with electrochemical experiments. The typical equilibrium potential curve of graphite controls strongly the intercalation heterogeneity along thickness and this heterogeneity is maximal for state of charge corresponding to regions of flat equilibrium potential. Indeed, a flat equilibrium potential promotes lithiation disparities along thickness, whereas a variable equilibrium potential enhances a quick return to a homogeneous lithiated electrode. Current and mass loading affect proportionally these heterogeneities, which are linked with a decrease in cell performance. A correlation between heterogeneities and equivalent resistances interpolated from galvanostatic discharge is found. Pathway resistances calculated from simulation outputs indicate preferential locations of intercalation under operation, depending on the difference between the local and global equilibrium potential of the graphite electrode.
Carbon catalysts for electrochemical hydrogen peroxide production in acidic media Electrochim. Acta (IF 4.798) Pub Date : 2018-04-03 Viktor Čolić, Sungeun Yang, Zsolt Révay, Ifan E.L. Stephens, Ib Chorkendorff
Hydrogen peroxide is a commodity chemical, as it is an environmentally friendly oxidant. The electrochemical production of H2O2 from oxygen and water by the reduction of oxygen is of great interest, as it would allow the decentralized, on-site, production of pure H2O2. The ability to run the reaction in an acidic electrolyte with high performance is particularly important, as it would allow the use of polymer solid electrolytes and the production of pH-neutral hydrogen peroxide. Carbon catalysts, which are cheap, abundant, durable and can be highly selective show promise as potential catalysts for such systems. In this work, we examine the electrocatalytic performance and properties of seven commercially available carbon materials for H2O2 production by oxygen electroreduction. We show that the faradaic efficiencies for the reaction lie in a wide range of 18–82% for different carbon catalysts. In order to determine the cause of these differences, we employ prompt gamma ray/neutron activation analysis and XPS measurements to assess the contribution of heteroatoms and defects, as well as low temperature N2-adsorption and transmission electron microscopy to elucidate the particle size, shape, BET surface area and porosity. We find that the surface oxygen groups, nitrogen and sulphur content display effects that are not straightforward, because their chemical state is likely significant. The metal content (when present in the order of magnitude of ∼10 ppm) is not a straightforward indicator of the electrocatalytic performance for this reaction. XPS and BET data indicate that carbons displaying high selectivities for the 2-electron process contain more aliphatic-like, “defect” structures on the surface.
Medulla tetrapanacis-derived O/N co-doped porous carbon materials for efficient oxygen reduction electrocatalysts and high-rate supercapacitors Electrochim. Acta (IF 4.798) Pub Date : 2018-04-03 Bei Liu, Mei Yang, Duanguang Yang, Hongbiao Chen, Huaming Li
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