Alkaline Electrolyte Research Articles

Promoting Electrochemical CO2 Reduction to Formate via Sulfur‐Assisted Electrolysis

AbstractElectrochemical CO2 reduction reaction (CO2RR) provides a renewable approach to transform CO2 to produce chemicals and fuels. Unfortunately, it faces the challenges of sluggish CO2 activation and slow water dissociation. This study reports the modification of Bi‐based electrocatalyst by S, which leads to a remarkable enhancement in activity and selectivity during electrochemical CO2 reduction to formate. Based on comprehensive in situ examinations and kinetic evaluations, it is observed that the presence of S species over Bi catalyst can significantly enhance its interaction with K+(H2O)n, facilitating fast dissociation of water molecules to generate protons. Further in situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) and in situ Raman spectroscopy measurements reveal that S modification is able to decrease the oxidation state of Bi active site, which can effectively enhance CO2 activation and facilitate HCOO* intermediate formation while suppressing competing hydrogen evolution reaction. Consequently, the S‐modified Bi catalyst achieves impressive electrochemical CO2RR performance, reaching a formate Faradaic efficiency (FEformate) of 91.2% at a formate partial current density of ≈135 mA cm−2 and a potential of −0.8 V versus RHE in an alkaline electrolyte.

Development of Transition Metal Phosphates NiCoP/NF and Evaluation of Their Hydrogen Evolution Properties

Energy and the environment are one of the most important global issues in the 21st century. In order to avoid the excessive destruction of the environment and human settlements by fossil fuels, and achieve sustainable development of the Earth, clean energy carrier hydrogen shows its application value. Facing the challenges in preparing transition metal phosphides, in this study, transition metal salts and urea were used as raw materials to react under hydrothermal conditions. The transition metal basic carbonate NiCo2(CO3)1.5OH3 was grown in situ on nickel-foam (NF) substrates. After low-temperature phosphating treatment, NiCoP alloy phosphide electrocatalysts (NiCoP/NF) grown on nickel-foam substrates were obtained. The electrochemical hydrogen evolution performance was tested in 1 mol/L KOH alkaline electrolyte solution. Experiments show, NiCoP/NF heterostructure catalyst has excellent hydrogen evolution performance. In an alkaline medium, the overpotential required to obtain the catalytic current density of 10 mA/cm2 is only 93 mV, and the Tafel slope is 118 mV/dec. This is largely due to: 1) the good dispersion of NiCoP/NF nano-catalyst on the Nickel Foam substrate increased the number of active sites exposed; 2) the heterostructure promotes the electron interaction between NiCoP and NF; 3) theoretical calculations show that the construction of NiCoP/NF heterostructure can effectively reduce the dissociation barrier of water, promote the dissociation of water, the kinetic reaction process of electrocatalytic hydrogen evolution is accelerated. Therefore, the construction of NiCoP/NF nanostructured heterogeneous catalysts enriches the application of non-noble metal nanomaterials in the field of hydrogen production from water electrolysis.

Shifting the Oxygen-Evolution Reaction Pathway via Cation Engineering to Activate Lattice Oxygen in Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) as promising electrocatalysts have been widely studied, but their performance is limited by conductivity and coordinating saturation. This study proposes a cationic (V) modification strategy and evaluates its effect on the electrocatalytic performance of CoFe-MOF nanosheet arrays. The optimal V-CoFe-MOF/NF electrocatalyst exhibits excellent oxygen-evolution reaction (OER)/hydrogen-evolution reaction (HER) performance (231 mV at 100 mA cm-2/86 mV at 10 mA cm-2) in alkaline conditions, with its OER durability exceeding 400 h without evident degradation. Furthermore, as a bifunctional electrocatalyst for water splitting, a small cell voltage is achieved (1.60 V at 10 mA cm-2). The practicability of the catalyst is further evaluated by membrane electrode assembly (MEA), showing outstanding activity (1.53 V at 10 mA cm-2) and long-term stability (at 300 mA cm-2). Moreover, our results reveal the apparent reconstruction properties of V-CoFe-MOF/NF in alkaline electrolytes, where the partially dissolved V promotes the formation of more active β-MOOH. The mechanism study shows the OER mechanism shifts to a lattice oxygen oxidation mechanism (LOM) after V doping, which directly avoids complex multistep adsorption mechanism and reduces reaction energy. This study provides a cation mediated strategy for designing efficient electrocatalysts.

Two-dimensional MXene supported Ru-Cr(OH)x clusters as an efficient electrocatalyst for hydrogen oxidation reaction

The development of high-performance non-platinum catalysts remains a key challenge for the practical application of anion-exchange membrane fuel cells due to the sluggish kinetics response of the hydrogen oxidation reaction (HOR) in alkaline electrolytes. Herein, we report an outstanding HOR electrocatalyst using a facile one-step method with the two-dimensional double transition metal MXene (Mo2TiC2Tx) as a carrier mixed with metallic ruthenium and Cr(OH)x clusters (Ru-Cr(OH)x/MXene). Specifically, the as-prepared Ru-Cr(OH)x/MXene electrocatalyst exhibits a high apparent kinetic current (jk) of 18.32 mA cm−2 and exchange current (j0) of 1.64 mA cm−2 at an overpotential of 50 mV, respectively, which are 4.74 and 1.46 times as high as those of Pt/C catalyst. Additionally, mechanism experiments indicated that the Ru-Cr(OH)x/MXene electrocatalyst could attenuate the adsorption of hydrogen intermediate (Had) and enhance the adsorption of hydroxyl species (OHad) to promote CO oxidation, which resulted in a significant increase in the HOR activity and enhanced tolerance to CO. Furthermore, combining theoretical studies via density functional theory calculations, our work confirm that the interaction effect of each components of Ru-Cr(OH)x/MXene can optimize the binding energy of the Had and OHad for the HOR. This work develops a new approach to design of HOR electrocatalyst with MXene-based materials.

Interface engineering of 2D NiFe LDH/NiFeS heterostructure for highly efficient 5-hydroxymethylfurfural electrooxidation

The electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to valuable chemicals is an efficient way to upgrade biomass molecules and replace traditional catalytic synthesis. It is crucial to develop efficient and low-cost earth-abundant electrocatalysts to enhance catalytic performance of HMF oxidation. Herein, a new type of two-dimensional (2D) hybrid arrays consisting of NiFe layered double hydroxides (LDH) nanosheets and bimetallic sulfide (NiFeS) is constructed via interface engineering for efficient electrocatalytic oxidation of HMF to 2,5-furandicarboxylic acid (FDCA). The preparation process of 2D NiFe LDH/NiFeS with ultrathin heterostructure involves in anchoring a Co-based metal-organic framework (Co MOF) as template onto the carbon cloth (CC) via in-situ growth, formation of NiFe LDH on the surface of Co MOF and subsequent partial sulfidation. The electrocatalyst of NiFe LDH/NiFeS exhibits outstanding performance towards HMF oxidation, about 98.5% yield for FDCA and 97.2% Faraday efficiency (FE) in the alkaline electrolyte with 10 mmol/L HMF, as well as excellent stability retaining 90.1% FE for FDCA after six cycles test. Moreover, even at an HMF concentration of 100 mmol/L, the yield and FE for FDCA remain high at 83.6% and 93.6%, respectively. These findings highlight that 2D heterostructure containing abundant interfaces between NiFe LDH nanosheets and NiFeS can enhance the intrinsic activity of LDH and thus promote the oxidation reaction kinetics. Additionally, the synergistic effect of the bimetallic NiFe compounds also improved the selectivity of HMF conversion to FDCA. Our present work demonstrates that constructing 2D ultrathin heterostructure of NiFe LDH/NiFeS is a facile strategy via interface engineering to enhance the intrinsic activity of LDH electrocatalysts, which would open new avenues toward low-cost and advanced 2D nanocatalysts for sustainable energy conversion and electrochemical valorization of biomass derivatives.

Accelerating H* desorption of hollow Mo2C nanoreactor via in-situ grown carbon dots for electrocatalytic hydrogen evolution

Molybdenum carbide (Mo2C) is a promising non-noble metal electrocatalyst with electronic structures similar to Pt for hydrogen evolution reaction (HER). However, strong H* adsorption at the Mo sites hinders the improvement of HER performance. Here, we synthesized monodisperse hollow Mo2C nanoreactors, in which the carbon dots (CD) were in situ formed onto the surface of Mo2C through carburization reactions. According to finite element simulation and analysis, the CD@Mo2C possesses better mesoscale diffusion properties than Mo2C alone. The optimized CD@Mo2C nanoreactor demonstrates superior HER performance in alkaline electrolyte with a low overpotential of 57 mV at 10 mA cm−2, which is better than most Mo2C-based electrocatalysts. Moreover, CD@Mo2C exhibits excellent electrochemical stability during 240 h, confirmed by operando Raman and X-ray diffraction (XRD). Density functional theory (DFT) calculations show that carbon dots cause the d-band center of CD@Mo2C to shift away from Fermi level, promoting water dissociation and the desorption of H*. This study provides a reasonable strategy towards high-activity Mo-based HER eletrocatalysts by modulating the strength of Mo–H bonds.

Synergistic M‐O Dual‐Atom Pairs Induced Interfacial Water Hydrogen Bonding Network for Boosting MoSe2 Electrocatalytic Performance

AbstractUnderstanding the dynamics changes of the water network at the electrode–solution interface during the hydrogen evolution reaction (HER) process, including how it is doubly regulated by the electrode material and electrolyte pH, and its subsequent effects on the reaction intermediates (H* and OH*), is crucial in electrochemistry. However, relevant studies are limited due to water's its dual role as both a reactant and a solvent. Thus, it is essential to construct an ideal model capable of decoupling the effects of interfacial water action from the surface catalytic HER process. In this study, M‐O atom pairs doped MoSe2 model catalyst is developed to achieve this goal and tailor the water network structure in a double‐layer microenvironment. Combined with molecular dynamics simulations and in situ spectroscopic characterization, correlations between water configuration, the water network, and water dissociation with HER activity are successfully established. This findings reveal that the pH‐dependent hydrogen‐bonding environment, modulated by oxophilic species, exerts a greater influence on acidic HER compared to alkaline media. The optimized Rh,O‐MoSe2‐x catalyst demonstrates exceptional performance in both acid and alkaline electrolytes and shows no activity decay during a PEMWE test at 1.5 A cm−2, making it promising for scalable water electrolyzers.

New insights into the photoassisted anodic reactions of n-type 4H SiC semiconductors

This study aims to investigate the photoelectrochemical behavior of the n-type 4H-SiC, focusing on aqueous, hydroxide-based electrolytes. Despite its high stability, this wide-bandgap semiconductor material undergoes electrochemical reactions, such as anodic oxidation or etching, under specific conditions. Since electrons are the majority charge carriers in n-type semiconductors, oxidation processes require above-bandgap illumination. Then, the reaction rate is influenced by the number of electron holes available for an oxidation process and the velocity of the transport of hydroxide ions to/from the surface. The goal is to focus on the essential reaction parameters (i.e., potential and electrolyte concentration) to clarify the reaction mechanism in aqueous (alkaline) electrolytes. Methods with controllable hydrodynamic conditions are required to investigate the transport processes in the electrolyte. Even though the rotating disk electrode (RDE) is a commonly used and powerful method, it is not well suited for our purpose. Photoelectrochemical etching of SiC is extraordinary because it involves both mass transfer phenomena and gas evolution but also needs high-intensity illumination from an appropriate light source. Hence, a new concept for an inverted rotating cell was developed and implemented. This setup was used to study the effect of the mass transport of hydroxide ions on the photoelectrochemical behavior of SiC in each potential region at varying rotation speeds. In order to interpret the experimental findings, a distinct electrical network model was formulated for simulating the results, aiding in unraveling the underlying reaction mechanism. Electrochemical measurements were complemented by surface-sensitive analytical techniques. XPS was the method of choice to investigate the composition of the sample surface before and after etching. SEM and AFM allow the characterization of the surface morphology in the initial stages of etching. The totality of this information provides a complete picture of the complex processes in the vicinity of the semiconductor electrode.Graphical abstract

How multi-level porous carbon structure affects electrocatalytic properties?

For zinc-air batteries, it is crucial to develop bifunctional electrocatalysts that exhibit exceptional activity, high stability, and low cost. Based on this, three-dimensional carbon-based catalysts with multiple pore sizes were successfully prepared by using three different combinations of soluble salts as hard templates for controlling morphology and structure. These catalysts are denoted as 3D Co/NCBMS. Because of the synergistic effect of heteroatomic doping and a multi-level porous structure, 3D Co/NCBMS exhibits better catalytic properties for OER and ORR, comparable to IrO2 and Pt/C. The half-wave potential of the 3D Co/NCBMS catalyst was 0.82 V (vs RHE) in the ORR reaction and 1.54 V in the OER reaction. 3D Co/NCBMS samples exhibit excellent stability, maintaining a charge and discharge efficiency of approximately 54 % after stable cycling for 225 h. It also demonstrates high resistance to methanol poisoning, with the current remaining at around 95 % in alkaline electrolyte solutions when assembled into zinc-air batteries.

Efficient Decoupled Electrolytic Water Splitting in Acid through Pseudocapacitive TiO2.

Water electrolysis remains a key component in the societal transition to green energy. Membrane electrolyzers are the state-of-the-art technology for water electrolysis, relying on 80°C operation in highly alkaline electrolytes, which is undesirable for many of the myriad end-use cases for electrolytic water splitting. Herein, an alternative water electrolysis process, decoupled electrolysis, is described which performed in mild acidic conditions with excellent efficiencies. Decoupled electrolysis sequentially performs the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), at the same catalyst. Here, H+ ions generated from the OER are stored through pseudocapacitive (redox) charge storage, and released to drive the HER. Here, decoupled electrolysis is demonstrated using cheap, abundant, TiO2 for the first time. To achieve decoupled acid electrolysis, ultra-small anatase TiO2 particles (4.5nm diameter) are prepared. These ultra-small TiO2 particles supported on a carbon felt electrode show a highly electrochemical surface area with a capacitance of 375Fg-1. When these electrodes are tested for decoupled water splitting an overall energy efficiency of 52.4% is observed, with excellent stability over 3000 cycles of testing. This technology can provide a viable alternative to membrane electrolyzers-eliminating the need for highly alkaline electrolytes and elevated temperatures.

Attaining Substantially Enhanced Oxygen Evolution Reaction Rates on Ni Foam Catalysts in a Gas Diffusion Electrode Setup

Water electrolysis plays a central role in the transition to a fossil‐free society, but there are significant challenges to overcome in order to increase its availability on a large scale. Alkaline water electrolysis is a mature and scalable technology, although it has several disadvantages compared to electrolyzers working in acidic environments. In particular, the use of highly alkaline aqueous electrolytes can lead to corrosion, and the achieved current densities are relatively low. This study addresses the latter limitation by introducing a gas diffusion electrode (GDE) setup as a novel development tool that bridges the gap between research and practical applications in commercial devices such as fuel cells and electrolyzers. A high surface area Ni foam catalyst that can sustain exceptional oxygen evolution reaction (OER) current densities of up to 4 A cm−2 in a quasi‐steady‐state within our GDE setup operating in an alkaline environment is presented. The high performance of this Ni‐based benchmark catalyst is attributed to its deposition onto a mesh‐like porous transport layer (PTL) via hydrogen‐templated electrodeposition. This forms a porous foam‐like structure that augments the mass transport of the gaseous reactants at the GDE.

Synthesis of nitrogen and sulfur bi-doped carbon obtained from spent sapelli wood sawdust and polyhydric alcohol with improved catalytic activity for hydrogen evolution reaction

Developing an efficient water electrolysis system is an important solution for on the development of highly active, cost-effective, and stable electrocatalysts. Carbon-based metal-free catalysts are one of the promising candidates for this purpose. Herein, we present a facile strategy to synthesize and characterize nitrogen and sulfur co-doped porous carbon (NS-PC) from spent sapelli wood sawdust and polyhydric alcohol (xylitol) for efficient hydrogen evolution reaction (HER) in alkaline electrolyte. The resultant NS-PC metal-free catalyst exhibits porous structure, high surface areas and enhanced HER performance with lowest Tafel slope of 68.1 mV dec−1. The enhanced performance is due to the high porosity of carbonaceous material and co-existence of active species (N in the forms of graphitic-N, pyridinic-N, pyrrolic-N, and S in the forms of C–S–C) induced by the maximum carbon-carbon bond polarization, charge re-distribution in the carbon matrices with a synergistically HER activity. In addition, this work provides a versatile and effective strategy for synthetizing excellent carbon-based metal free catalysts from the low cost biowaste for large-scale production of hydrogen through HER.

Self-supported Ru-Fe-Ox nanospheres as efficient electrocatalyst to boost overall water-splitting in acid and alkaline media

Developing electrocatalysts with high activity and durability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in both acidic and alkaline electrolytes remains challenging. In this study, we synthesize a self-supported ruthenium-iron oxide on carbon cloth (Ru-Fe-Ox/CC) using solvothermal methods followed by air calcination. The morphology of the nanoparticle exposes numerous active sites vital for electrocatalysis. Additionally, the strong electronic interaction between Ru and Fe enhances electrocatalytic kinetics optimization. The porous structure of the carbon cloth matrix facilitates mass transport, improving electrolyte penetration and bubble release. Consequently, Ru-Fe-Ox/CC demonstrates excellent catalytic performance, achieving low overpotentials of 32 mV and 28 mV for HER and 216 mV and 228 mV for OER in acidic and alkaline electrolytes, respectively. Notably, only 1.48 V and 1.46 V are required to reach 10 mA cm−2 for efficient water-splitting in both mediums, exhibiting remarkable stability. This research offers insights into designing versatile, highly efficient catalysts suitable for varied pH conditions.

Polyoxometalate coupled polymers induced molybdenum phosphide with large surface area for efficient hydrogen evolution

Developing highly active hydrogen evolution reaction (HER) electrocatalysts possesses great significance for the green renewable energy conversion and storage. Here, through the electrostatic attraction between polyoxometalate (PMo12) and ammonium polyphosphate (APP) and the coordination with polyallylamine hydrochloride (PAH), the precursor was constructed, and then nitrogen-doped graphite carbon layer-coated MoP active particles (MoP@NC) were successfully prepared by high temperature carbonization. For HER, the overpotential of η10 for MoP@NC is 119 and 126 mV in acidic and alkaline electrolyte. Furthermore, in alkaline solution, when the current density reaches a certain degree (≥110 mA cm−2), the hydrogen production activity of the catalysts are the same as that of the industrial Pt/C catalysts, or even have a slight advantage. The synergistic interaction of active particles (MoP) and graphitic carbon layers and high specific surface area ensure the excellent activity of HER. N-doped porous carbon layers also protect MoP@NC working for 24 h. Moreover, the catalysts prepared in the same experimental environment with ammonium molybdate as metal source also showed good HER performance in acidic and alkaline environments. This study opens a general way to develop earth-rich Mo-based phosphide electrocatalysts with high activity for hydrolysis applications.

Self-Assembled Conjugated Coordination Polymer Nanorings: Role of Morphology and Redox Sites for the Alkaline Electrocatalytic Oxygen Evolution Reaction.

Electrocatalytic water splitting provides a sustainable method for storing intermittent energies, such as solar energy and wind, in the form of hydrogen fuel. However, the oxygen evolution reaction (OER), constituting the other half-cell reaction, is often considered the bottleneck in overall water splitting due to its slow kinetics. Therefore, it is crucial to develop efficient, cost-effective, and robust OER catalysts to enhance the water-splitting process. Transition-metal-based coordination polymers (CPs) serve as promising electrocatalysts due to their diverse chemical architectures paired with redox-active metal centers. Despite their potential, the rational use of CPs has faced obstacles including a lack of insights into their catalytic mechanisms, low conductivity, and morphology issues. Consequently, achieving success in this field requires the rational design of ligands and topological networks with the desired electronic structure. This study delves into the design and synthesis of three novel conjugated coordination polymers (CCPs) by leveraging the full conjugation of terpyridine-attached flexible tetraphenylethylene units as electron-rich linkers with various redox-active metal centers [Co(II), Ni(II), and Zn(II)]. The self-assembly process is tuned for each CCP, resulting in two distinct morphologies: nanosheets and nanorings. The electrocatalytic OER performance efficiency is then correlated with factors such as the nanostructure morphology and redox-active metal centers in alkaline electrolytes. Notably, among the three morphologies studied, nanorings for each CCP exhibit a superior OER activity. Co(II)-integrated CCPs demonstrate a higher activity between the redox-active metal centers. Specifically, the Co(II) nanoring morphology displays exceptional catalytic activity for OER, with a lower overpotential of 347 mV at a current density of 10 mA cm-2 and small Tafel slopes of 115 mV dec-1. The long-term durability is demonstrated for at least 24 h at 1.57 V vs RHE during water splitting. This is presumably the first proof that links the importance of nanostructure morphologies to redox-active metal centers in improving the OER activity, and it may have implications for other transdisciplinary energy-related applications.

Effect of a Physisorbed Tetrabutylammonium Cation Film on Alkaline Hydrogen Evolution Reaction on Pt Single-Crystal Electrodes.

The addition of tetrabutylammonium (TBA+) to alkaline electrolytes enhances the hydrogen evolution reaction (HER) activity on Pt single-crystal electrodes. The concentration of TBA+ significantly influences the HER on Pt(111). Concentrations of ≤1 mM yield no significant effect on HER currents or the coverage of adsorbed hydrogen (H*) but exhibit an interaction with the OHads on the surface. Conversely, concentrations of >1 mM result in an apparent site-blocking effect for underpotential-deposited H* caused by the physisorption of the organic cation, which counterintuitively leads to an increase in the HER activity. The physisorption of TBA+ is linked to its accumulation in the diffuse layer, as it can be reversibly removed by the addition of nonadsorbing cations such as sodium. Following the previous literature on the TBA+ interaction with electrode surfaces, we ascribe this effect to the formation of a two-dimensional TBA+ film in the double layer. On stepped Pt single-crystal surfaces, TBA+ enhances HER activity at all concentrations, primarily at step sites. Our findings not only highlight the complexities of TBA+ accumulation on Pt electrodes but also offer important molecular-level insights for optimizing the HER by organic film formation on various atomic-level electrode structures.

Heterogeneous strategy constructing a built-in electric field: CoP/FeP bifunctional electrode for overall water splitting

Development of non-noble bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are of great significance under alkaline electrolytes for overall water splitting. In this work, CoP/FeP has been designed and constructed in situ on carbon fiber paper by using the bimetallic metal organic frameworks (MOFs) synthesis strategy. The heterogeneous CoP/FeP displays excellent catalytic activities in both HER and OER of the fully hydrolyzed semi-reaction. Remarkably, CoP/FeP is applied as the bifunctional electrode in anode and cathode to construct an overall water splitting apparatus, resulting in the low cell voltage and excellent stability. The exceptional electrocatalytic performance may be mainly attributed to the heterogeneous interface, which constructs a built-in electric field to provide electron to Co with electron-rich structure, resulting in the strong adsorption of H and weak adsorption of O2 on Co. This study provides an effective and controllable method for the design of self-supporting bimetal phosphide catalysts.

Substantial Electrocatalytic Oxygen Evolution Performances of Activated Carbon-Decorated Vanadium Pentoxide Nanocomposites

Developing the ecofriendly and high-fidelity electrocatalysts for the oxygen evolution reaction (OER) is essential to foster effective production of environmentally friendly hydrogen. Herein, we fabricated the highly efficient OER electrocatalysts of the activated carbon-decorated vanadium pentoxide (AC-V2O5) nanocomposites using a facile hydrothermal technique. The AC-V2O5 nanocomposites displayed an aggregated structure of the AC nano-sheet-anchored orthorhombic V2O5 nanorods. When performing the OER process in an alkaline electrolyte at 10 mA/cm2, AC-V2O5 exhibited the low overpotential (~230 mV), small Tafel slope (~54 mV/dec), and excellent stability. These substantial OER performances of AC-V2O5 could be ascribed to the synergistic effects from both the electrochemically active V2O5 nanorods and the highly conductive AC nanosheets. The results infer that the AC-V2O5 nanocomposites possess a substantial aptitude as a high-performance OER electrocatalyst for production of the future green energy source—hydrogen.

Unique ping-pong daisy-like catalysts: Efficient overall hydrolysis catalysis driven by vanadium-doped Fe2P and Co3(PO4)2 nanosheet composites

Balancing catalytic activity and durability remains a challenge in the development of high performance, inexpensive and durable electrocatalysts. In this study, fully hydrolyzed composite catalyst V–Fe2P@Co3(PO4)2/NF with ping-pong daisy-like morphology was synthesized using conventional hydrothermal and chemical vapor deposition (CVD) processes. In alkaline electrolyte, V–Fe2P@Co3(PO4)2/NF showed excellent electrochemical performance, achieving a current density of 10 mA cm−2 when the driving overpotentials for the hydrogen production reaction (HER) and oxidation reaction (OER) were 56 mV and 178 mV, respectively. Meanwhile, V–Fe2P@Co3(PO4)2/NF demonstrated good durability in terms of both HER and OER stability. Furthermore, the driving voltage required for the electrolyser assembled with V–Fe2P@Co3(PO4)2/NF as the electrode is lower than that of the RuO2/NF||Pt/C/NF electrode, both of which have driving voltages of 1.503 and 1.562 V (10 mA cm−2), respectively. Meanwhile, it achieves a Faraday efficiency of 95%. This study offers a feasible solution towards synthesizing and applying bifunctional water decomposition electrocatalysts.

Surface modified FeCoZn-ZIF derived polyhedral electrocatalysts for ORR under alkaline and acidic conditions

Electrocatalysts for catalyzing oxygen reduction reactions at variable pH conditions are essential for energy conversion and storage. Herein, Fe@FeCoZn–CN electrocatalysts were prepared with internal and external doping approach. The Fe@FeCoZn–CN electrocatalyst exhibits a desirable ORR performance in both acid and alkaline electrolytes. Specifically, the half-wave potential (E1/2) of Fe@FeCoZn–CN electrocatalyst is 0.890 V which far beyond Pt/C electrocatalyst (0.839 V) in alkaline electrolyte. In addition, Fe@FeCoZn–CN electrocatalyst also exhibits improved ORR activity (E1/2 = 0.801 V) compared to Pt/C (0.797 V) electrocatalysts in acidic electrolytes. What's exciting is that the rechargeable ZABs based on Fe@FeCoZn–CN electrocatalysts exhibit an impressive performance with a favorable open-circuit potential of 1.517 V and a promising specific capacity is 833.7 mA h gzn−1, good charge/discharge cycle stability. The remarkable ORR catalytic performance of Fe@FeCoZn–CN electrocatalysts can be traced to the internal doping of metals which prevent excessive metal aggregation and surface modified which can increase the metal loading to expose more active sites.