Full Length ArticleHierarchical Pd/MnO2 nanosheet array supported on Ni foam: An advanced electrode for electrocatalytic hydrodechlorination reaction
Graphical abstract
Introduction
Halogenated organic compounds, including halogenated chain and aromatic hydrocarbons, are an important class of chemical and industrial feedstock with wide applications in pharmaceutical, agricultural and polymer industries. The large-scale use, however, increases their exposure and impact in ecotope [1]. As the leading member of persistent organic pollutants, these halogenated compounds are stable in chemical structure, and highly resistant to natural degradation. They can also be easily accumulated in living bodies via food chain, exerting long-term harms to organs and immune systems [2]. In this case, the technologies that can remove them in an effective and green manner are highly desired [3], [4], [5], [6], [7], [8]. Electrocatalytic hydrodechlorination (EHDC) represents one promising alternative by its high efficiency, mild condition, green feature and low secondary pollution risk [9], [10]. In EHDC, numerous atomic hydrogen (H*) were in situ produced from aqueous solution at cathode via electrolysis of water, which served as the reductive agent to attack and cleave C-Cl bond, converting halogenated organics to their nonhalogenated analogues and chloride ions [11], [12], [13].
The metallic palladium (Pd) was one priority cathode catalyst due to its high efficiency and durability in producing H* from aqueous solution at a wide pH range [14], [15]. Additionally, it showed strong power in adsorption and activation of the halogenated pollutants for sequent hydrodechlorination reaction [16]. However, Pd is one precious metal, and its low earth-abundance forces us to maximize its mass activity and reduce consumption. Engineering the particle into a nanoscale is one efficient strategy, which enabled to raise the exposure of Pd atoms at particle surface, making them accessible for the desired reactions [17], [18], [19]. To further improve the performance, these NPs were supported on the metallic Ti, Cu or Ni foam substrate that owned a self-supported three-dimensional (3D) porous structure facilitating the pollutant mass diffusion [20], [21], [22]. Cheng reported the first Pd NP/Ti mesh electrode for removal of 2,4-dichlorophenol [23]. Since then, various foam electrodes, such as the Pd/Ni foam and Pd/Cu foam electrode, were developed [24], [25], [26]. However, as the Pd NPs were grown on the foam via a simple spontaneous galvanic reaction between the foam metal and a Pd salt, their dispersion and size were usually not well-controlled, making their overall mass activity still unsatisfactory. On the other hand, the intrinsic activity of Pd in these electrodes was actually not improved, due to the little synergy between Pd and the support in EHDC.
In recent years, the researchers found that decoration of the foam electrode with some other active species can significantly promote the mass activity of Pd. He ever deposited an Ag or Cu layer between the Ni foam and Pd NPs, and found that the presence of Ag improved the dispersion of Pd NPs and contributed to the adsorption of pollutants on electrode [27], [28]. Instead, Mao decorated the Cu foam with N-doped graphene (N-GR) before the loading of Pd, and identified that N-GR contributed to an enhanced H* generation [29]. Sun introduced the conductive polymer in electrodes, which was proved to promote NP dispersion and H* generation [30]. Xu ever modified the Pd/Ni foam electrode with TiN or TiC NPs as both of these NPs could contribute a promotional synergy for H* generation [31], [32]. The oxides with the metal component of diverse valences (such as MnO2 and TiO2) represented another important class of active additives. Lou ever deposited the Pd NPs on Ni foam with its skeleton covered by layers of MnO2. Their experimental results confirmed that the introduction of MnO2 could reduce the Pd NP size, and enhance H* generation at the Pd-MnO2 interfaces, leading to a significant enhancement in mass activity [33], [34]. In addition, the hydrophilic features of the oxide benefited the mass diffusion of reactants around electrode.
In this work, we developed another more efficient Pd/MnO2-Ni foam electrode for EHDC of 2,4-dichlorophenol (2,4-DCP, one typical halogenated organic pollutant). In contrast to that in Lou’s work with a compact layer structure, the MnO2 in our work displayed a uniform nanosheet array structure with much larger surface areas. Notably, sequent Pd depositing was conducted by pre-constructing oxygen vacancies on MnO2 sheet by a reductive current, which served as the active sites to catch and reduce Pd2+ to Pd. By our binder-free approach, the formed Pd NPs are small in size (around 3.5 nm), well dispersed on MnO2 nanosheet array and form strong interactions with MnO2. As expected, the Pd/MnO2-Ni foam electrode displayed an unprecedented high EHDC performance and mass activity in batch experiments, in comparison to the Pd/Ni foam and that reported in known literatures. The cathode potential and coexisting anions effect on EHDC performance of Pd/MnO2-Ni foam electrode were then investigated. Given the robust EHDC performance, the electrode was applied into a continuous flow EHDC system to assess its feasibility in practical applications. Finally, the real role of MnO2 played during the EHDC was explored.
Section snippets
Materials
Ni foam substrate (Pore density: 110 PPI; Porosity: 98%; Surface density: 380 g m−2) was obtained from Kunshan Tengerhui Electronic Technology Co., Ltd., China. Analytical grade of anhydrous ethanol, 2,4-dichlorophenol (2,4-DCP), p-chlorophenol (p-CP), o-chlorophenol (o-CP), phenol (P), sodium sulfate (Na2SO4), sodium chloride (NaCl), sodium nitrate (NaNO3), sodium nitrite (NaNO2), sodium sulfide nonahydrate (Na2S·9H2O), palladium chloride (PdCl2) and potassium permanganate (KMnO4), as well as
Electrode characterization
The hierarchical 3D Pd/MnO2-Ni foam electrode was fabricated by a facile multistep process, as schematically illustrated in Fig. 2. At the first step, the MnO2 nanosheet array was grown on the skeleton of Ni foam (MnO2-Ni foam) via a hydrothermal reaction. The formed MnO2-Ni foam was then subjected to a reductive current, by which partial Mn (IV) was reduced to low valences and some oxygen vacancies formed on MnO2 sheet [37], [38]. The resultant MnOx-Ni foam was quickly immersed into a Pd2+
Conclusions
This work developed one advanced Pd/MnO2-Ni foam composite electrode for EHDC, which featured a self-supported 3D network structure, hierarchical skeleton surface and improved Pd dispersion. With these merits, the electrode delivered an unprecedented high mass activity (kobs) of 0.883 min−1 mmolPd−1 for EHDC of 2,4-DCP, which was nearly ten times that of the Pd/Ni foam electrode (0.081 min−1 mmolPd−1). The electrode also displayed robust durability in the repeated batch EHDC experiments till
CRediT authorship contribution statement
Junxi Li: Methodology, Investigation, Writing - original draft. Yiyin Peng: Investigation, Writing - original draft. Wendong Zhang: Formal analysis. Xuelin Shi: Investigation. Min Chen: Project administration. Peng Wang: Validation. Xianming Zhang: Resources. Hailu Fu: Software. Xiaoshu Lv: Data curation, Visualization. Fan Dong: Writing - review & editing. Guangming Jiang: Conceptualization, Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The present work is financially supported by National Natural Science Foundation of China (51878105), Venture & Innovation Support Program for Chongqing Overseas Returnees (cx2017066), the Program for the Top Young Talents of Chongqing, Scientific and Technological Research Program of Chongqing Municipal Education Commission (KJQN201800829, KJZD-M201900802 and KJZD-K201800801), Research Startup Foundation of Chongqing Technology and Business University (2016-56-01 and 2016-56-02), Scientific
References (60)
- et al.
Hydrodechlorination of 1,2-dichloroethane on supported AgPd catalysts
J. Catal.
(2019) - et al.
Unique selectivity in the hydrodechlorination of 2,4-dichlorophenol over hematite-supported Au
J. Catal.
(2013) - et al.
Insight into the kinetics and mechanism of removal of aqueous chlorinated nitroaromatic antibiotic chloramphenicol by nanoscale zero-valent irons
Chem. Eng. J.
(2018) - et al.
Enhanced electrocatalytic dechlorination by dispersed and moveable activated carbon supported palladium catalyst
Chem. Eng. J.
(2019) - et al.
Electrocatalytic dechlorination of halogenated antibiotics via synergistic effect of chlorine-cobalt bond and atomic H*
J. Hazard. Mater.
(2018) - et al.
2,4-Dichlorophenol removal from water using an electrochemical method improved by a composite molecularly imprinted membrane/bipolar membrane
J. Hazard. Mater.
(2019) - et al.
Electrocatalytic dechlorination of chloropicolinic acid mixtures by using palladium-modified metal cathodes in aqueous solutions
Electrochim. Acta
(2016) - et al.
Electrocatalytic hydrodechlorination of 2,4-dichlorophenol over palladium nanoparticles and its pH-mediated tug-of-war with hydrogen evolution
Chem. Eng. J.
(2018) - et al.
Aqueous-phase hydrodechlorination of 4-chlorophenol on palladium nanocrystals: Identifying the catalytic sites and unraveling the reaction mechanism
J. Catal.
(2018) - et al.
Two-dimensional covalent-organic- framework-derived nitrogen-rich carbon nanosheets modified with small Pd nanoparticles for the hydrodechlorination of chlorophenols and hydrogenation of phenol
Appl. Catal. A: Gen.
(2018)
Hydrodechlorination catalysis of Pd-on-Au nanoparticles varies with particle size
J. Catal.
Electrocatalytic activity of Pd-loaded Ti/TiO2 nanotubes cathode for TCE reduction in groundwater
Water Res.
Enhanced electrocatalytic dechlorination of para-chloronitrobenzene based on Ni/Pd foam electrode
Chem. Eng. J.
Engineering aspects of electrochemical hydrodehalogenation of 2,4-dichlorophenol in a solid polymer electrolyte reactor
Appl. Catal. A: Gen.
A novel electrode of ternary CuNiPd nanoneedles decorated Ni foam and its catalytic activity toward NaBH4 electrooxidation
Electrochim. Acta
Electrodeposition of palladium and reduced graphene oxide nanocomposites on foam-nickel electrode for electrocatalytic hydrodechlorination of 4-chlorophenol
J. Hazard. Mater.
High-performance electrocatalytic hydrodechlorination of pentachlorophenol by amorphous Ru-loaded polypyrrole/foam nickel electrode
Electrochim. Acta
Increasing the activity and stability of chemi-deposited palladium catalysts on nickel foam substrate by electrochemical deposition of a middle coating of silver
Sep. Purif. Technol.
Effect of silver or copper middle layer on the performance of palladium modified nickel foam electrodes in the 2-chlorobiphenyl dechlorination
J. Hazard. Mater.
Dechlorination of triclosan by enhanced atomic hydrogen-mediated electrochemical reduction: Kinetics, mechanism, and toxicity assessment
Appl. Catal. B: Environ.
Complete dechlorination of 2,4-dichlorophenol in aqueous solution on palladium/polymeric pyrrole-cetyl trimethyl ammonium bromide/foam-nickel composite electrode
J. Hazard. Mater.
TiC doped palladium/nickel foam cathode for electrocatalytic hydrodechlorination of 2,4-DCBA: Enhanced electrical conductivity and reactive activity
J. Hazard. Mater.
Influence of environmental factors on the electrocatalytic dechlorination of 2,4-dichlorophenoxyacetic acid on nTiN doped Pd/Ni foam electrode
Chem. Eng. J.
Insight into atomic H* generation, H2 evolution, and cathode potential of MnO2 induced Pd/Ni foam cathode for electrocatalytic hydrodechlorination
Chem. Eng. J.
MnO2 enhances electrocatalytic hydrodechlorination by Pd/Ni foam electrodes and reduces Pd needs
Chem. Eng. J.
Facile synthesis of ultrathin manganese dioxide nanosheets arrays on nickel foam as advanced binder-free supercapacitor electrodes
J. Power Sources
Multi-layer monoclinic BiVO4 with oxygen vacancies and V4+ species for highly efficient visible-light photoelectrochemical applications
Appl. Catal. B: Environ.
Electrochemically self-doped TiO2 nanotube arrays for efficient visible light photoelectrocatalytic degradation of contaminants
Electrochim. Acta
Advanced electrochemical energy storage supercapacitors based on the flexible carbon fiber fabric-coated with uniform coral-like MnO2 structured electrodes
Chem. Eng. J.
Pd-TiO2 schottky heterojunction catalyst boost the electrocatalytic hydrodechlorination reaction
Chem. Eng. J.
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These two authors contribute equally to this work.