Low Oxygen Evolution Reaction Overpotential Research Articles

CuNi alloy anchored on dual-substrate TiOx/N-doped carbon nanofibers as a bifunctional electrocatalyst for rechargeable zinc-air batteries

Development of non-noble metal-based electrocatalysts to enhance the performance of zinc-air batteries (ZABs) is of great significance, but it remains a formidable challenge due to their poor stability and activity. Herein, a bifunctional CuNi-TiOx/NCNFS electrocatalyst, featuring with electron-rich copper-nickel (CuNi) alloy nanoparticles anchored on titanium oxide/N-doped carbon nanofibers (TiOx/NCNFS), is constructed by a dual-substrate loading strategy. The introduction of TiOx has led to a significant increase in the stability of the dual-substrate. The strong electronic interaction between CuNi and TiOx strengthens the anchoring of active metal sites, thus accelerating the electron transfer. Theoretical calculations unclose that NCNFS can regulate the charge distribution of TiOx, inducing the charge transfer from NCNFS → TiOx → CuNi, thereby reducing the d-band center of Cu and Ni, which is beneficial to the desorption of intermediate oxide species of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Therefore, CuNi-TiOx/NCNFS delivers a remarkable bifunctional performance with a low OER overpotential of 258 mV at 10 mA cm−2 and an ORR half-wave potential of 0.85 V. When assembled into ZABs, CuNi-TiOx/NCNFS shows a low potential gap of 0.64 V, a higher power density of 149.6 mW cm−2 at 330 mA cm−2, and an outstanding stability for 250 h at 5mA cm−2. This study provides a novel approach by constructing dual-substrate to tune the electronic structure of active metal sites for efficient rechargeable ZABs.

Raney nickel induced interface modulation of active NiFe-hydroxide as efficient and robust electrocatalyst towards oxygen evolution reaction

Preparation of active and durable low-cost catalysts towards oxygen evolution reaction (OER) is essential for alkaline water splitting. Herein, porous Raney-Ni supported NiFe-LDH (NiFe-LDH/Raney-Ni) electrocatalyst was developed to achieve efficient and robust OER performance. Raney-Ni modulates the NiFe-LDH electronic structure by interfacial interaction. In-situ infrared shows the enhanced OH adsorption behavior, and in-situ Raman suggests that Raney-Ni promotes the formation of active NiFeOOH species on NiFe-LDH/Raney-Ni. Theoretical calculations found that the Fe atoms in NiFe-LDH/Raney-Ni enhances the charge transfer to the NiOOH species, which facilitates the formation of O* intermediates accelerating the OER process. The NiFe-LDH/Raney-Ni catalyst exhibits a low OER overpotential of 219 mV at 10 mA cm−2 in 1 M KOH with excellent stability for 200 h at 200 mA cm−2. Excellent performance is also achieved in alkaline electrolyzer test. This work presents a facile approach for the design of affordable and efficient alkaline OER electrocatalysts.

Designing a Phenalenyl-Based Dinuclear Ni(II) Complex: An Electrocatalyst with Two Single Ni Sites for the Oxygen Evolution Reaction (OER).

A new dinuclear Ni(II) complex 1, [Ni2II(dtbh-PLY)2], is synthesized from 9-(2-(3,6-di-tert-butyl-2-hydroxybenzylidene)hydrazineyl)-1H-phenalen-1-one, dtbh-PLYH2 ligand, and structurally characterized by various analytical tools including the single-crystal X-ray diffraction (SCXRD) technique. In the solid state, both Ni(II) metal centers in complex 1 exist in a distorted square planar geometry and display the presence of rare Ni···H-C anagostic interactions to form a one-dimensional (1-D) linear motif in the supramolecular array. Complex 1 is further stabilized in the solid state by π-π-stacking interactions between the highly delocalized phenalenyl rings. The redox features of complex 1 have been analyzed by the cyclic voltammetry (CV) technique in solution as well as in the solid state, revealing the crucial involvement of both the Ni(II) metal centers for undergoing quasi-reversible oxidation reactions on the application of an anodic sweep. A complex 1-modified glassy carbon electrode, GC-1, is employed as an electrocatalyst for oxygen evolution reaction (OER) in 1.0 M KOH, giving an OER onset at 1.45 V, and very low OER overpotential, 300 mV vs the reversible hydrogen electrode (RHE) to reach 10 mA cm-2 current density. Furthermore, GC-1 displayed fast OER kinetics with a Tafel slope of 40 mV dec-1, a significantly lower Tafel slope value than those of previously reported molecular Ni(II) catalysts. In situ electrochemical experiments and postoperational UV-vis, Fourier transform infrared (FT-IR), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) studies were performed to analyze the stability of the molecular nature of complex 1 and to gain reasonable insights into the true OER catalyst.

WO3-x as an activation medium to prompt overall water splitting of NiFe-based electrocatalyst

The efficient oxygen evolution reaction (OER) is crucial for various electrochemical processes, especially for overall water splitting (OWS). In this study, we focus on the utilization of WO3-x as an activation medium to enhance the OER performance of NiFe-based electrocatalysts. Firstly, we synthesize WO3-x nanowires supported on nickel foam (NF) and then incorporate NiFe on WO3-x nanowires by a simple hydrothermal method. The WO3-x self-supported NiFe (Oxy)hydroxide (denoted as NiFe-W-O/NF) shows a three-dimensional stereostructure composed of ultrathin nanosheets (∼ 4.0 nm). This unique structure provides a large open surface for fuller diffusion of the electrolyte while exposing more active sites. The electronic interaction of tri-centers of NiFeW accelerates the surface reconstruction process of γ-NiOOH and FeOOH, which are converted into the main active species in a short time. The electrochemical measurements confirm that the NiFe-W-O/NF has low OER overpotentials (233 mV at 10 mA cm−2, 298 mV at 100 mA cm−2) and excellent stability (100 h in total) in 1 M KOH electrolyte. In addition, the NiFe-W-O/NF || NiFe-W-O/NF battery also exhibits a low cell voltage (1.52 V at 10 mA cm−2) with a stable lifetime (50 h) under alkaline conditions. These results highlight the great potential of NiFe-W-O/NF for practical applications.

High-throughput screening of dual atom catalysts for oxygen reduction and evolution reactions and rechargeable zinc-air battery

We provide the rational design of dual atom catalysts (DACs) supported on nitrogen-doped graphene for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through high-throughput computational screening of M1M2N6-DAC systems, where M1 and M2 represent Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt metals. We predict that FeRuN6-DAC at the summit of the volcano plot exhibits a low theoretical ORR overpotential (ηORR) of 0.24 V and a low theoretical OER overpotential (ηOER) of 0.19 V. The low ηORR and ηOER result from the catalytic performance of the Fe site being tuned to electronic properties that facilitate adsorption and desorption of the OH* intermediate. Inspired by these hybrid density functional theory (DFT) computational and machine learning (ML) results, we synthesized FeRuN6-DAC, FeN4-SAC, and RuN4-SAC and characterized them using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and in-situ electron spin resonance (ESR). Our in-situ ESR spectroscopy signifies that the spin of the Fe active site increases with increasing applied potential due to the increase in the concentration of OH* intermediate on Fe. We verified experimentally the predicted catalytic performances, finding that FeRuN6-DAC leads to an experimental ORR overpotential of 0.29 V with a Tafel slope of 104 mVdec−1 and an OER overpotential of 0.27 V with a Tafel slope of 124 mVdec−1. The rechargeable Zinc-air battery setup was fabricated with FeRuN6-DAC in place of the cathode, showing a maximum power density of 0.45 W/cm2 at the current density of 0.44 A/cm2 and good stability after 120 cycles. According to our findings, we demonstrate that DFT-guided strategies are useful for designing advanced DACs applicable to ORR, OER, and Zinc-air battery applications.

Polarized Ultrathin BN Induced Dynamic Electron Interactions for Enhancing Acidic Oxygen Evolution

AbstractDeveloping ruthenium‐based heterogeneous catalysts with an efficient and stable interface is essential for enhanced acidic oxygen evolution reaction (OER). Herein, we report a defect‐rich ultrathin boron nitride nanosheet support with relatively independent electron donor and acceptor sites, which serves as an electron reservoir and receiving station for RuO2, realizing the rapid supply and reception of electrons. Through precisely controlling the reaction interface, a low OER overpotential of only 180 mV (at 10 mA cm−2) and long‐term operational stability (350 h) are achieved, suggesting potential practical applications. In situ characterization and theoretical calculations have validated the existence of a localized electronic recycling between RuO2 and ultrathin BN nanosheets (BNNS). The electron‐rich Ru sites accelerate the adsorption of water molecules and the dissociation of intermediates, while the interconnection between the O‐terminal and B‐terminal edge establishes electronic back‐donation, effectively suppressing the over‐oxidation of lattice oxygen. This study provides a new perspective for constructing a stable and highly active catalytic interface.

Composite-induced FeO(OH) phase transition as a highly efficient electrocatalyst for robust overall water splitting

Realizing efficient and stable overall water electrolysis is crucial for advancing efficient hydrogen production. However, developing electrocatalysts with both efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance under alkaline condition remains a significant challenge. Here, we report an innovative methodology for synthesizing FeO(OH)@NiC2O4 on nickel foam (NF) through a one-step hydrothermal method. Remarkably, FeO(OH)@NiC2O4/NF exhibits a remarkably low OER overpotential of 370 mV at a current density of 100 mA cm−2 and excellent electrochemical stability in OER. The cell voltage required for overall water splitting is lower than that of most reported catalysts. Detailed experiments reveal that the phase transition of FeO(OH) is induced through compositing, thereby significantly enhancing the catalytic performance.

Polarized Ultrathin BN Induced Dynamic Electron Interactions for Enhancing Acidic Oxygen Evolution.

Developing ruthenium-based heterogeneous catalysts with an efficient and stable interface is essential for enhanced acidic oxygen evolution reaction (OER). Herein, we report a defect-rich ultrathin boron nitride nanosheet support with relatively independent electron donor and acceptor sites, which serves as an electron reservoir and receiving station for RuO2, realizing the rapid supply and reception of electrons. Through precisely controlling the reaction interface, a low OER overpotential of only 180 mV (at 10 mA cm-2) and long-term operational stability (350 h) are achieved, suggesting potential practical applications. In situ characterization and theoretical calculations have validated the existence of a localized electronic recycling between RuO2 and ultrathin BN nanosheets (BNNS). The electron-rich Ru sites accelerate the adsorption of water molecules and the dissociation of intermediates, while the interconnection between the O-terminal and B-terminal edge establishes electronic back-donation, effectively suppressing the over-oxidation of lattice oxygen. This study provides a new perspective for constructing a stable and highly active catalytic interface.

Glassy State Hydroxide Materials for Oxygen Evolution Electrocatalysis.

Hydroxides are the archetype of layered crystals with metal-oxygen (M-O) octahedron units, which have been widely investigated as oxygen evolution reaction (OER) catalysts. However, the better crystallinity of hydroxide materials, the more perfect octahedral symmetry and atomic ordering, resulting in the less exposed metal sites and limited electrocatalytic activity. Herein, a glassy state hydroxide material featuring with short-range order and long-range disorder structure is developed to achieve high intrinsic activity for OER. Specifically, a rapid freezing point precipitation method is utilized to fabricate amorphous multi-component hydroxide. Owing to the freezing-point crystallization environment and chaotic M-O (M = Ni/Fe/Co/Mn/Cr etc.) structures, the as-fabricated NiFeCoMnCr hydroxide exhibit a highly-disordered glassy structure, as-confirmed by X-ray/electron diffraction, enthalpic response, and pair distribution function analysis. The as-achieved glassy-state hydroxide materials display a low OER overpotential of 269mV at 20mA cm-2 with a small Tafel slope of 33.3mV dec-1 , outperform the benchmark noble-metal RuO2 catalyst (341mV, 84.9mV dec-1 ) . Operando Raman and density functional theory studies reveal that the glassy state hydroxide converted into disordered active oxyhydroxide phase with optimized oxygen intermediates adsorption under low OER overpotentials, thus boosting the intrinsic electrocatalytic activity.

Graphene Architecture-Supported Porous Cobalt-Iron Fluoride Nanosheets for Promoting the Oxygen Evolution Reaction.

The design of efficient oxygen evolution reaction (OER) electrocatalysts is of great significance for improving the energy efficiency of water electrolysis for hydrogen production. In this work, low-temperature fluorination and the introduction of a conductive substrate strategy greatly improve the OER performance in alkaline solutions. Cobalt-iron fluoride nanosheets supported on reduced graphene architectures are constructed by a one-step solvothermal method and further low-temperature fluorination treatment. The conductive graphene architectures can increase the conductivity of catalysts, and the transition metal ions act as electron acceptors to reduce the Fermi level of graphene, resulting in a low OER overpotential. The surface of the catalyst becomes porous and rough after fluorination, which can expose more active sites and improve the OER performance. Finally, the catalyst exhibits excellent catalytic performance in 1 M KOH, and the overpotential is 245 mV with a Tafel slope of 90 mV dec-1, which is better than the commercially available IrO2 catalyst. The good stability of the catalyst is confirmed with a chronoamperometry (CA) test and the change in surface chemistry is elucidated by comparing the XPS before and after the CA test. This work provides a new strategy to construct transition metal fluoride-based materials for boosted OER catalysts.

Designing the major active site of Cu atom for OER via a composite electrocatalyst of Agx@HEO: Experiment and theory

Copper element with low chemical activity is hard to be used as the major active site for oxygen evolution reaction (OER). To improve its OER performance, a specialized structural and chemical environments need be designed. In this work, the composite electrocatalyst of Agn@HEO were synthesized by a simple co-precipitation plus annealing methods. With the aid of the elemental Ag0 atom, part of Cu ions in high entropy oxide (HEO) phases were gradually transferred to the elemental Cu0 atoms and mixed with Ag0 atom for CuAg alloy. This transition evidently altered the chemical environments of Cu element. Thanks to the largest molar percentage of Cu0 atom, the designed Ag1@HEO specimen exhibited the fairly low experimental OER overpotential of 249 (308) mV at the current density of 10 (100) mA cm−2 with the small Tafel slope of 55.2 mV dec-1 and stable electrocatalytic activity. Based on the density functional theory simulation, the theoretical OER overpotential of Cu active site could be adjusted along with the ridges of “volcanic” in both atomic and ionic environments, and achieved the smallest value of 213 mV as the d band center of Cu0 atom had a suitable value near the “volcanic” peak. This design strategy would be adopted to provide an effective enhancement scheme for OER on Cu active site.

Nanoengineered, Pd-doped Co@C nanoparticles as an effective electrocatalyst for OER in alkaline seawater electrolysis

Water electrolysis is considered one of the major sources of green hydrogen as the fuel of the future. However, due to limited freshwater resources, more interest has been geared toward seawater electrolysis for hydrogen production. The development of effective and selective electrocatalysts from earth-abundant elements for oxygen evolution reaction (OER) as the bottleneck for seawater electrolysis is highly desirable. This work introduces novel Pd-doped Co nanoparticles encapsulated in graphite carbon shell electrode (Pd-doped CoNPs@C shell) as a highly active OER electrocatalyst towards alkaline seawater oxidation, which outperforms the state-of-the-art catalyst, RuO2. Significantly, Pd-doped CoNPs@C shell electrode exhibiting low OER overpotential of ≈213, ≈372, and ≈ 429 mV at 10, 50, and 100 mA/cm2, respectively together with a small Tafel slope of ≈ 120 mV/dec than pure Co@C and Pd@C electrode in alkaline seawater media. The high catalytic activity at the aforementioned current density reveals decent selectivity, thus obviating the evolution of chloride reaction (CER), i.e., ∼490 mV, as competitive to the OER. Results indicated that Pd-doped Co nanoparticles encapsulated in graphite carbon shell (Pd-doped CoNPs@C electrode) could be a very promising candidate for seawater electrolysis.

Stabilizing non-iridium active sites by non-stoichiometric oxide for acidic water oxidation at high current density

Stabilizing active sites of non-iridium-based oxygen evolution reaction (OER) electrocatalysts is crucial, but remains a big challenge for hydrogen production by acidic water splitting. Here, we report that non-stoichiometric Ti oxides (TiOx) can safeguard the Ru sites through structural-confinement and charge-redistribution, thereby extending the catalyst lifetime in acid by 10 orders of magnitude longer compared to that of the stoichiometric one (Ru/TiO2). By exploiting the redox interaction-engaged strategy, the in situ growth of TiOx on Ti foam and the loading of Ru nanoparticles are realized in one step. The as-synthesized binder-free Ru/TiOx catalyst exhibits low OER overpotentials of 174 and 265 mV at 10 and 500 mA cm−2, respectively. Experimental characterizations and theoretical calculations confirm that TiOx stabilizes the Ru active center, enabling operation at 10 mA cm−2 for over 37 days. This work opens an avenue of using non-stoichiometric compounds as stable and active materials for energy technologies.

Interconnected nickel cobalt vanadate quasi-spheres as an efficient and stable oxygen evolution electrocatalyst in alkaline media

The present work reports the one-step hydrothermal fabrication of carbon fiber paper (CFP) supported interconnected nickel cobalt vanadate (Ni3-xCoxV2O8) microparticles. The CFP substrate was selected for its conductive support and strong adhesion to materials, thereby improving durability. Crystal structure analysis confirmed the successful incorporation of Co into the Ni3V2O8 lattice, resulting in a single orthorhombic phase of Ni3-xCoxV2O8 without altering the crystal structure. Compositional tuning was achieved by varying Ni/Co molar feeding ratios to optimize electrocatalytic oxygen evolution reaction (OER) performance in 1 M KOH. The compositionally tuned interconnected NiCo2V2O8 microspheres exhibited improved OER activity compared to its individual counterparts and other compositions. It exhibited a low OER overpotential of ∼ 351 mV to reach a current density of 50 mA cm−2 and good long-term stability for 20 h, without any performance decay. These results suggest that the NiCo2V2O8 could serve as a cost-effective alternative to valuable electrocatalysts for the alkaline OER.

Synergistic two-dimensional metal sulfide heterostructures from ZIF-67: A promising catalyst for efficient overall water splitting

The morphology of nanomaterials plays a significant role in electrocatalytic water splitting. Metal–organic frameworks (MOFs) offer several advantages, including high porosity, large specific surface area, adjustable structure and various morphologies. Among the various MOFs, zeolitic imidazolate framework-67 (ZIF-67) is a cobalt-based MOF that can produce carbon-containing metal sulfides through appropriate sulfurization and annealing processes. Since the control of the morphology of nanostructured electrocatalysts plays a crucial role in optimizing catalytic activity, in this study, we synthesized rhombic dodecahedral, cubic, and plate-shaped ZIF-67 nanocrystals and utilized them as templates to fabricate Co3S4@CoMoS3 nanomaterials with various morphologies. These materials were characterized and subjected to electrochemical tests to evaluate their performance in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrocatalytic water splitting. The electrochemical measurements revealed that the plate-shaped Co3S4@CoMoS3–P exhibited the low overpotential for OER at 20 mA cm−2, with a value of 200 mV and a Tafel slope of 173 mV dec−1. Similarly, for HER at 10 mA cm−2, it showed an overpotential of 240 mV and a Tafel slope of 93 mV dec−1. Moreover, in the water splitting setup employing a dual electrode configuration, the plate-shaped Co3S4@CoMoS3–P achieved a voltage of 1.61 V at 20 mA cm−2, outperforming a commercial electrode combination (10% Pt/C//RuO2) in terms of water-splitting efficiency.

Enhancing Oxygen Evolution Reaction by Simultaneously Triggering Metal and Lattice Oxygen Redox Pair in Iridium Loading on Ni‐Doped Co3O4

AbstractSince the active sites in catalytic systems are either metal sites or lattice oxygen, simultaneously triggering metal and lattice oxygen redox pair with low energy barriers is expected to provide diversified and efficient sites to accelerate oxygen evolution reaction (OER) kinetics, but this is a great challenge. Herein, Ir species (Ir clusters and Ir single atoms) loaded on Ni‐doped Co3O4 is designed (Ir/Ni‐Co3O4), where metallic Ir clusters downsize to spread into high‐density Ir single atoms to load on reconstruction‐derived Ni‐doped CoOOH. In situ spectroscopy, isotope‐labeled, and chemical probe experiments demonstrate that metal site and lattice oxygen are simultaneously activated to participate in the OER. Further theoretical studies demonstrate that the Co site is the most favorable site to promote the OER through an adsorbate evolution mechanism with a low energy barrier of 1.69 eV. The Ni cooperating with Ir atoms synergistically upshifts energy positions of the O p band centers. Thus, the lattice O that bridges Ni and Ir atoms is activated to participate in the OER via coupling with adsorbed O on the Ir site to fulfill O─O bond formation. Benefiting from the conjoint participation of the metal and lattice oxygen redox pair, Ir/Ni‐Co3O4 affords extremely low OER overpotentials of 177 and 263 mV at corresponding 10 and 500 mA cm−2.

Spin-State Modulation on Metal-Organic Frameworks for Electrocatalytic Oxygen Evolution.

Electrochemical oxygen evolution reaction (OER) kinetics are heavily correlated with hybridization of the transition metal d-orbital and oxygen intermediate p-orbital, which dictates the barriers of intermediate adsorption/desorption on the active sites of catalysts. Herein, a strategy is developed involving strain engineering and coordination regulation to enhance the hybridization of Ni 3d and O 2p orbitals, and the as-synthesized Ni-2,6-naphthalenedicarboxylic acid metal-organic framework (DD-Ni-NDA) nanosheets deliver a low OER overpotential of 260mV to reach 10mAcm-2 . By integrating an alkaline anion exchange membrane electrolyzer and Pt/C electrode, 200 and 500mAcm-2 current densities are reached with cell voltages of 1.6 and 2.1V, respectively. When loaded on a BiVO4 photoanode, the nanosheet enables highly active solar-driven water oxygen. Structural characterizations together with theoretical calculations reveal that the spin state of the centre Ni atoms is regulated by the tensile strain and unsaturated coordination defects in DD-Ni-NDA, and such spin regulation facilitates spin-dependent charge transfer of the OER. Molecular orbital hybridization analysis reveals the mechanism of OH* and OOH* adsorption energy regulation by changes in the DD-Ni-NDA spin state, which provides a deeper understanding of the electronic structure design of catalysts for the OER.

Transition metal doped WSi2N4 monolayer for water splitting electrocatalysts: a first-principles study

High-performance water splitting electrocatalysts are urgently needed in the face of the environmental degradation and energy crisis. The first principles method was used in this study to systematically examine the electronic characteristics of transition metal (Sc, Ti, V, Cr, Mn, Fe, and Ru) doped WSi2N4 (TM@WSi2N4) and its potential as oxygen evolution reaction (OER) catalysts. Our study shows that the doping of TM atoms significantly improves the catalytic performance of TM@WSi2N4, especially Fe@WSi2N4 shows a low overpotential (η OER = 470 mV). Interestingly, we found that integrated-crystal orbital Hamilton population and d-band center can be used as descriptors to explain the high catalytic activity of Fe@WSi2N4. Subsequently, Fe@WSi2N4 exhibits the best hydrogen evolution reaction (HER) activity with a universal overpotential of 47 mV on N1 sites. According to our research, Fe@WSi2N4 offers a promising substitute for precious metals as a catalyst for overall water splitting with low OER and HER overpotentials.

A superhydrophilic NiFe electrode for industrial alkaline water electrolysis

NiFe-based materials are among the most promising alkaline oxygen evolution reaction (OER) catalysts because of their high intrinsic activities and abundance. Although many advanced NiFe-based catalysts have been developed, few exhibit simultaneous high activity, stability, good mass transfer, and cost-effective large-scale preparation. Furthermore, NiFe-based catalysts have rarely been studied in alkaline water electrolyzers (AWE) where the catalysts work under a large current density in an alkaline electrolyte at high temperatures and high concentrations with tight assembly pressure. This study successfully developes robust and highly active NiFe nanocone array (NA) catalysts that exhibit both fast and cost-effective mass production capabilities. Benefiting from the in situ-formed OER-active NiFe layered double hydroxide (LDH) and the superhydrophilic structure-induced fast mass transfer, the optimized NiFe NA sample presentes a low OER overpotential of 269 mV at 500 mA cm−2 in a 30 wt% KOH solution. The NiFe core-NiFe LDH shell structure and metallic bond between NiFe nanocones and the substrate are crucial for enabling the NiFe electrode to maintain a minimal potential increase of only 4% even after 250 h of testing at 500 mA cm−2 in a 30 wt% KOH solution. Moreover, the AWE using NiFe NA anodes and NiMo cathodes (NiFe//NiMo) works stably at 500 mA cm−2 under 80 °C in 30 wt% KOH solution and presents a power energy consumption of 4.0 kWh Nm−3 H2, much lower than that of the Ni mesh//Ni mesh counterpart and most commercial AWEs. This study, for the first time, evaluates the performance of NiFe electrodes in AWE and demonstrates their industrial application prospects in alkaline water electrolysis.

Kinetically accelerated oxygen evolution reaction in metallic (oxy)hydroxides enabled by Cr-dopant and heterostructure

Efficient water-splitting is an underpinning technology for producing hydrogen in high-purity and enabling hydrogen economy, but it suffers from the sluggish kinetics of anodic oxygen evolution reaction (OER). Cost-efficient transition metals-based oxides/hydroxides, particularly NiFe-based double hydroxides (NiFe LDHs), have been deemed as promising OER electrocatalysts in alkaline electrolytes. However, their electrocatalytic performance still waits to be substantially optimized. Herein, we demonstrate the tremendously enhanced OER activity of NiFe LDH via a developed coupling strategies of intrinsic chromium (Cr) doping and external heterojunction engineering. Relying on the heterostructure, an in-built electric field is proved and thus the charge transfer kinetic is substantially accelerated. Remarkably, the synergistic surface electron modulation, explicitly revealed by theoretical calculation and experimental analysis, elucidates that the upward d-band center of Fe sites after doping Cr accounts for the much-enhanced OER activity, being inherited when combining with CuO substrate, while the increased empty d orbital of Ni sites after introducing CuO part interprets the activation of initially nonactive Ni sites. As a result, a low OER overpotential of 210 mV (at 10 mA cm−2) and excellent durability are achieved for Cr-NiFe LDH@CuO catalyst. Furthermore, the resultant alkaline electrolyzer also displays outstanding activity (requires a low voltage of 1.56 V at 100 mA cm−2) and good durability.