Engineering an Earth‐Abundant Element‐Based Bifunctional Electrocatalyst for Highly Efficient and Durable Overall Water Splitting

The simultaneous and efficient evolution of hydrogen and oxygen with earth‐abundant, highly active, and robust bifunctional electrocatalysts is a significant concern in water splitting. Herein, non‐noble metal‐based Ni–Co–S bifunctional catalysts with tunable stoichiometry and morphology are realized. The engineering of electronic structure and subsequent morphological design synergistically contributes to significantly elevated electrocatalytic performance. Stable overpotentials (η₁₀) of 243 mV (vs reversible hydrogen electrode) for oxygen evolution reaction (OER) and 80 mV for hydrogen evolution reaction (HER), as well as Tafel slopes of 54.9 mV dec^?1 for OER and 58.5 mV dec^?1 for HER, are demonstrated. In addition, density functional theory calculations are performed to determine the optimal electronic structure via the electron density differences to verify the enhanced OER activity is related to the Co top site on the (110) surface. Moreover, the tandem bifunctional NiCo₂S₄ exhibit a required voltage of 1.58 V (J = 10 mA cm^?2) for simultaneous OER and HER, and no obvious performance decay is observed after 72 h. When integrated with a GaAs solar cell, the resulting photoassisted water splitting electrolyzer shows a certified solar‐to‐hydrogen efficiency of up to 18.01%, further demonstrating the feasibility of engineering protocols and the promising potential of bifunctional NiCo₂S₄ for large‐scale overall water splitting.     

Efficient Optimization of Electron/Oxygen Pathway by Constructing Ceria/Hydroxide Interface for Highly Active Oxygen Evolution Reaction

Owing to the unique electronic properties, rare‐earth modulations in noble‐metal electrocatalysts emerge as a critical strategy for a broad range of renewable energy solutions such as water‐splitting and metal–air batteries. Beyond the typical doping strategy that suffers from synthesis difficulties and concentration limitations, the innovative introduction of rare‐earth is highly desired. Herein, a novel synthesis strategy is presented by introducing CeO₂ support for the nickel–iron–chromium hydroxide (NFC) to boost the oxygen evolution reaction (OER) performance, which achieves an ultralow overpotential at 10 mA cm^?2 of 230.8 mV, the Tafel slope of 32.7 mV dec^?1, as well as the excellent durability in alkaline solution. Density functional theory calculations prove the established d–f electronic ladders, by the interaction between NFC and CeO₂, evidently boosts the high‐speed electron transfer. Meanwhile, the stable valence state in CeO₂ preserves the high electronic reactivity for OER. This work demonstrates a promising approach in fabricating a nonprecious OER electrocatalyst with the facilitation of rare‐earth oxides to reach both excellent activity and high stability.     

Electro‐Oxidation of Ni42 Steel: A Highly Active Bifunctional Electrocatalyst

Janus type water‐splitting catalysts have attracted highest attention as a tool of choice for solar to fuel conversion. AISI Ni42 steel is upon harsh anodization converted into a bifunctional electrocatalyst. Oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are highly efficiently and steadfast catalyzed at pH 7, 13, 14, 14.6 (OER) and at pH 0, 1, 13, 14, 14.6 (HER), respectively. The current density taken from long‐term OER measurements in pH 7 buffer solution upon the electro‐activated steel at 491 mV overpotential (η) is around four times higher (4 mA cm^?2) in comparison with recently developed OER electrocatalysts. The very strong voltage–current behavior of the catalyst shown in OER polarization experiments at both pH 7 and at pH 13 are even superior to those known for IrO₂‐RuO₂. No degradation of the catalyst is detected even when conditions close to standard industrial operations are applied to the catalyst. A stable Ni‐, Fe‐oxide based passivating layer sufficiently protects the bare metal for further oxidation. Quantitative charge to oxygen (OER) and charge to hydrogen (HER) conversion are confirmed. High‐resolution XPS spectra show that most likely γ?NiO(OH) and FeO(OH) are the catalytic active OER and NiO is the catalytic active HER species.     

Bifunctional Nickel Phosphide Nanocatalysts Supported on Carbon Fiber Paper for Highly Efficient and Stable Overall Water Splitting

Self‐supported electrodes comprising carbon fiber paper (CP) integrated with bifunctional nickel phosphide (Ni‐P) electrocatalysts are fabricated by electrodeposition of Ni on functionalized CP, followed by a convenient one‐step phosphorization treatment in phosphorus vapor at 500 °C. The as‐fabricated CP@Ni‐P electrode exhibits excellent electrocatalytic performance toward hydrogen evolution in both acidic and alkaline solutions, with only small overpotentials of 162 and 250 mV, respectively, attaining a cathodic current density of 100 mA cm^?2. Furthermore, the CP@Ni‐P electrode also exhibits superior catalytic performance toward oxygen evolution reaction (OER). An exceptionally high OER current of 50.4 mA cm^?2 is achieved at an overpotential of 0.3 V in 1.0 m KOH. The electrode can sustain 10 mA cm^?2 for 180 h with only negligible degradation, showing outstanding durability. Detailed microstructural and compositional studies reveal that upon OER in alkaline solution the surface Ni‐P is transformed to NiO covered with a thin Ni(OH)_x layer, forming a Ni‐P/NiO/Ni(OH)_x heterojunction, which presumably enhances the electrocatalytic performance for OER. Given the well‐defined bifunctionality, a full alkaline electrolyzer is constructed using two identical CP@Ni‐P electrodes as cathode and anode, respectively, which can realize overall water splitting with efficiency as high as 91.0% at 10 mA cm^?2 for 100 h.     

Boosting Activity on Co4N Porous Nanosheet by Coupling CeO2 for Efficient Electrochemical Overall Water Splitting at High Current Densities

Developing highly active nonprecious electrocatalysts with superior durability for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial to improve the efficiency of overall water splitting but remains challenging. Here, a novel superhydrophilic Co₄N‐CeO₂ hybrid nanosheet array is synthesized on a graphite plate (Co₄N‐CeO₂/GP) by an anion intercalation enhanced electrodeposition method, followed by high‐temperature nitridation. Doping CeO₂ into Co₄N can favor dissociation of H₂O and adsorption of hydrogen, reduce the energy barrier of intermediate reactions of OER, and improve the compositional stability, thereby dramatically boosting the HER performance while simultaneously inducing enhanced OER activity. Furthermore, the superhydrophilic self‐supported electrode with Co₄N‐CeO₂ in situ grown on the conductive substrate expedites electron conduction between substrate and catalyst, promotes the bubble release from electrode timely and impedes catalyst shedding, ensuring a high efficiency and stable working state. Consequently, the Co₄N‐CeO₂/GP electrode shows exceptionally low overpotentials of 24 and 239 mV at 10 mA cm^?2 for HER and OER, respectively. An alkaline electrolyzer by using Co₄N‐CeO₂/GP as both the cathode and anode requires a cell voltage of 1.507 V to drive 10 mA cm^?2, outperforming the Pt/C||RuO₂ electrolyzer (1.540 V@10 mA cm^?2). More significantly, the electrolyzer has extraordinary long‐term durability at a large current density of 500 mA cm^?2 for 50 h, revealing its potential in large‐scale applications.     

A Type of 1 nm Molybdenum Carbide Confined within Carbon Nanomesh as Highly Efficient Bifunctional Electrocatalyst

Highly efficient platinum‐alternative bifunctional catalysts by using abundant non‐noble metal species are of critical importance to the future sustainable energy reserves. Unfortunately, current electrocatalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are far from satisfactory because of lacking reasonable design and assembly protocols. A type of 1‐nm molybdenum carbide nanoparticles confined in mesh‐like nitrogen‐doped carbon (Mo₂C@NC nanomesh) with high specific surface area is reported here. In addition to the superior ORR performance comparable to platinum, the catalyst offers a high HER activity with small Tafel slope of 33.7 mV dec^?1 and low overpotential of 36 mV to reach ?10 mA cm^?2. Theoretical calculations indicate that the active sites of the catalyst are mainly located at Mo atoms adjacent to the N‐doped carbon layer, which contributes the high HER activity. These findings show the great potential of Mo₂C species in wide electrocatalysis applications.     

Amorphous Cobalt–Iron Hydroxide Nanosheet Electrocatalyst for Efficient Electrochemical and Photo‐Electrochemical Oxygen Evolution

Finding efficient electrocatalysts for oxygen evolution reaction (OER) that can be effectively integrated with semiconductors is significantly challenging for solar‐driven photo‐electrochemical (PEC) water splitting. Herein, amorphous cobalt–iron hydroxide (CoFe? H) nanosheets are synthesized by facile electrodeposition as an efficient catalyst for both electrochemical and PEC water oxidation. As a result of the high electrochemically active surface area and the amorphous nature, the optimized amorphous CoFe? H nanosheets exhibit superior OER catalytic activity in alkaline environment with a small overpotential (280 mV) to achieve significant oxygen evolution (j = 10 mA cm^?2) and a low Tafel slope (28 mV dec^?1). Furthermore, CoFe? H nanosheets are simply integrated with BiVO₄ semiconductor to construct CoFe? H/BiVO₄ photoanodes that exhibit a significantly enhanced photocurrent density of 2.48 mA cm^?2 (at 1.23 V vs reversible hydrogen electrode (RHE)) and a much lower onset potential of 0.23 V (vs RHE) for PEC‐OER. Careful electrochemical and optical studies reveal that the improved OER kinetics and high‐quality interface at the CoFe? H/BiVO₄ junction, as well as the excellent optical transparency of CoFe? H nanosheets, contribute to the high PEC performance. This study establishes amorphous CoFe? H nanosheets as a highly competitive candidate for electrochemical and PEC water oxidation and provides general guidelines for designing efficient PEC systems.     

Physically Adsorbed Metal Ions in Porous Supports as Electrocatalysts for Oxygen Evolution Reaction

Developing highly efficient and earth‐abundant electrocatalysts for the oxygen evolution reaction (OER) is significantly important for water‐splitting. Here, for the first time it is reported that the physically adsorbed metal ions (PAMI) in porous materials can be served as highly efficient OER electrocatalysts, which provides a universal PAMI method to develop electrocatalysts. This PAMI method can be applied to almost all porous supports, including graphene, carbon nanotubes, C₃N₄, CaCO₃, and porous organic polymers and all the systems exhibit excellent OER performance. In particular, the as‐synthesized Co_0.7Fe_0.3CB exhibits a small overpotential of 295 mV and 350 mV at the current density of 10 mA cm^?2 and 100 mA cm^?2, respectively, which exceeds commercial 40 wt% IrO₂/CB and most reported non‐noble metal‐based OER catalysts. Moreover, the mass activity of Co_0.7Fe_0.3CB reaches 643.4 A g^?1 at the overpotential of 320 mV, which is nearly 4.7 times higher than that of 40 wt% IrO₂/CB. In addition, the advanced ex situ and in situ synchrotron X‐ray characterizations are carried out to unravel the PAMI synthetic process. In short, this PAMI method will break the conversional understanding, i.e., the most OER catalysts are synthesized chemically, because the new PAMI method does not require any chemical synthesis, which therefore opens a new avenue for the development of OER electrocatalysts.     

Hybrid 2D Dual‐Metal–Organic Frameworks for Enhanced Water Oxidation Catalysis

Metal–organic frameworks (MOFs) and MOF‐derived nanostructures are recently emerging as promising catalysts for electrocatalysis applications. Herein, 2D MOFs nanosheets decorated with Fe‐MOF nanoparticles are synthesized and evaluated as the catalysts for water oxidation catalysis in alkaline medium. A dramatic enhancement of the catalytic activity is demonstrated by introduction of electrochemically inert Fe‐MOF nanoparticles onto active 2D MOFs nanosheets. In the case of active Ni‐MOF nanosheets (Ni‐MOF@Fe‐MOF), the overpotential is 265 mV to reach a current density of 10 mA cm^?2 in 1 m KOH, which is lowered by ≈100 mV after hybridization due to the 2D nanosheet morphology and the synergistic effect between Ni active centers and Fe species. Similar performance improvement is also successfully demonstrated in the active NiCo‐MOF nanosheets. More importantly, the real catalytic active species in the hybrid Ni‐MOF@Fe‐MOF catalyst are unraveled. It is found that, NiO nanograins (≈5 nm) are formed in situ during oxygen evolution reaction (OER) process and act as OER active centers as well as building blocks of the porous nanosheet catalysts. These findings provide new insights into understanding MOF‐based catalysts for water oxidation catalysis, and also shed light on designing highly efficient MOF‐derived nanostructures for electrocatalysis.     

Promoting Active Sites in Core–Shell Nanowire Array as Mott–Schottky Electrocatalysts for Efficient and Stable Overall Water Splitting

Developing earth‐abundant, active, and robust electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a vital challenge for efficient conversion of sustainable energy sources. Herein, metal–semiconductor hybrids are reported with metallic nanoalloys on various defective oxide nanowire arrays (Cu/CuO_x, Co/CoO_x, and CuCo/CuCoO_x) as typical Mott–Schottky electrocatalysts. To build the highway of continuous electron transport between metals and semiconductors, nitrogen‐doped carbon (NC) has been implanted on metal–semiconductor nanowire array as core–shell conductive architecture. As expected, NC/CuCo/CuCoO_x nanowires arrays, as integrated Mott–Schottky electrocatalysts, present an overpotential of 112 mV at 10 mA cm^?2 and a low Tafel slope of 55 mV dec^?1 for HER, simultaneously delivering an overpotential of 190 mV at 10 mA cm^?2 for OER. Most importantly, NC/CuCo/CuCoO_x architectures, as both the anode and the cathode for overall water splitting, exhibit a current density of 10 mA cm^?2 at a cell voltage of 1.53 V with excellent stability due to high conductivity, large active surface area, abundant active sites, and the continuous electron transport from prominent synergetic effect among metal, semiconductor, and nitrogen‐doped carbon. This work represents an avenue to design and develop efficient and stable Mott–Schottky bifunctional electrocatalysts for promising energy conversion.     

Unveiling Role of Sulfate Ion in Nickel-Iron (oxy)Hydroxide with Enhanced Oxygen-Evolving Performance

The rational design of effective catalysts for sluggish oxygen evolution reactions (OERs) is desired but challenging. Nickel-iron (NiFe) (oxy)hydroxides are promising pre-electrocatalysts for alkaline OER. However, OER performances are limited by the slow reconstruction process to generate active species of high-valance NiFe oxyhydroxides. In this work, a sulfate ion (SO₄²⁻) modulated strategy is developed to boost the OER activity of NiFe (oxy)hydroxide by accelerating the electrochemical reconstruction of pre-catalyst and stabilizing the reaction intermediate of OOH* during OER. The SO₄²⁻ decorated NiFe (oxy)hydroxide catalyst (NF-S0.15) is fabricated via scalable anodization of NiFe foam in a thiourea-dissolved electrolyte. The experimental and theoretical investigations demonstrate the dual effect of SO₄²⁻ on improving OER performances. SO₄²⁻ leaching is favorable for the electrochemical reconstruction to form active NiFeOOH under OER condition. Simultaneously, the residual SO₄²⁻ adsorbed on surface can stabilize the intermediate of OOH*, and thus enhance the OER performances. As expected, NF-S0.15 delivers an ultralow overpotential of 234 mV to reach the current density of 50 mA cm⁻², a fast OER kinetics (27.7 mV dec⁻¹), and a high stability for more than 100 h. This unique insights into anionic modification could inspire the development of advanced electrocatalysts for efficient OER.     

Nonprecious Intermetallic Al7Cu4Ni Nanocrystals Seamlessly Integrated in Freestanding Bimodal Nanoporous Copper for Efficient Hydrogen Evolution Catalysis

Tremendous demands for renewable hydrogen generated from water splitting have stimulated intensive research on developing earth‐abundant, non‐noble, and versatile metal catalysts toward the hydrogen evolution reactions (HER). Here, self‐supported Cu‐Ni‐Al hybrid electrodes that are composed of electroactive Al₇Cu₄Ni@Cu₄Ni core/shell nanocrystals seamlessly integrated in self‐supported 3D bimodal nanoporous Cu skeleton (Bi‐NP Cu/Al₇Cu₄Ni@Cu₄Ni) as robust HER electrocatalysts in alkaline electrolyte are reported. As a result of the proper architecture, in which the Bi‐NP Cu skeleton not only facilitates both electron and electrolyte transports but also provides high specific surface areas to fully use high electrocatalytic activity of Al₇Cu₄Ni@Cu₄Ni core/shell nanocrystals, the Bi‐NP Cu/Al₇Cu₄Ni@Cu₄Ni hybrid catalysts exhibit a low onset overpotential of 60 mV and a small Tafel slope of 110 mV dec^?1, enabling the catalytic current density of 10 mA cm^?2 at a low overpotential of 139 mV. The highly stable electrochemical performance makes them promising candidates as cathode catalysts in alkaline‐based devices.     

Controllable Synthesis of Nanosized Amorphous MoSx Using Temporally Shaped Femtosecond Laser for Highly Efficient Electrochemical Hydrogen Production

Amorphous molybdenum sulfide (a‐MoS_x) is regarded as a promising electrocatalyst for hydrogen evolution reaction (HER) due to its disorder structures with a significant number of defect‐rich active sites. Here, a green, one‐step, and controllable method is developed to photoregulate the chemical reactions and synthesize nanosized a‐MoS_x by temporally shaped femtosecond laser ablation of ammonium tetrathiomolybdate aqueous solution. By adjusting the laser energy and pulse delay to control photoinduced and/or photothermal‐induced reduction/oxidation, the S to Mo ratio x can be modulated from 1.53 to 3.07 and the ratio of the Mo^V defect species, bridging S₂^2?, and terminal S₂^2? ligands can be controlled. The optimized a‐MoS_x catalysts (x = 2.73) exhibit high catalytic activity with a low Tafel slope of 40 mV dec^?1, high double‐layer capacitance of 74.47 mF cm^?2, and large current density of 516 mA cm^?2 at an overpotential of 250 mV. The high catalytic activity can be mainly attributed to Mo^V defect species and bridging S₂^2? ligands, or most likely dominated by the Mo^V defect species. This study not only provides an alternatively controllable method to prepare a‐MoS_x as efficient HER catalysts but also contributes to the understanding of the origin of its catalytic activity.     

Pd Ion-Exchange and Ammonia Etching of a Prussian Blue Analogue to Produce a High-Performance Water-Splitting Catalyst

The authors report an ammonia-assisted in situ cation-exchange method for the synthesis of dodecagon N-doped PdCoNi carbon-based nanosheets (Pd-e-NiCo-PBA-C) and explore the catalytic performance. Pd-e-NiCo-PBA-C exerts extremely low overpotential and Tafel slope for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) both in acidic and alkaline media, only 47 mV, 55 mV dec⁻¹ (pH = 0, HER) and 147 mV, 67 mV dec⁻¹ (pH = 14, HER), and 309 mV, 67 mV dec⁻¹ (pH = 14, OER), outperforming commercial IrO₂-based and Pt-based catalysts. In addition, after 5000 cycles, the linear sweep voltammetry curve shows a negligible shift, indicating excellent stability performance. To test its overall water-splitting performance, Pd-e-NiCo-PBA-C is applied as both cathode and anode materials. A high current density of 33 mA cm⁻² at a battery voltage of 1.6 V is obtained, with the catalytic activity maintained at 97.3% after over 50 h. To get a further insight into the superior OER and HER performance, theoretical calculations are carried out, the better performance originates from the affinity difference of Pd and Ni atoms for gas atoms, and the replacement of inert atoms can decrease the binding energy and enhance the electrocatalytic activity.     

Synthesis of CeOx‐Decorated Pd/C Catalysts by Controlled Surface Reactions for Hydrogen Oxidation in Anion Exchange Membrane Fuel Cells

Due to the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline electrolytes, the development of more efficient HOR catalysts is essential for the next generation of anion‐exchange membrane fuel cells (AEMFCs). In this work, CeO_x is selectively deposited onto carbon‐supported Pd nanoparticles by controlled surface reactions, aiming to enhance the homogenous distribution of CeO_x and its preferential attachment to Pd nanoparticles, to achieve highly active CeO_x‐Pd/C catalysts. The catalysts are characterized by inductively coupled plasma–atomic emission spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy, scanning transmission electron microscopy (STEM), electron energy loss spectroscopy, and X‐ray photoelectron spectroscopy to confirm the bulk composition, phases present, morphology, elemental mapping, local oxidation, and surface chemical states, respectively. The intimate contact between Pd and CeO_x is shown through high‐resolution STEM maps. The oxophilic nature of CeO_x and its effect on Pd are probed by CO stripping. The interfacial contact area between CeO_x and Pd nanoparticles is calculated for the first time and correlated to the electrochemical performance of the CeO_x‐Pd/C catalysts. Highest recorded HOR specific exchange current (51.5 mA mg^?1_Pd) and H₂–O₂ AEMFC performance (peak power density of 1,169 mW cm^?2 mg_Pd^?1) are obtained with a CeO_x‐Pd/C catalyst with Ce_0.38/Pd bulk atomic ratio.     

High‐Performance Metal‐Free Nanosheets Array Electrocatalyst for Oxygen Evolution Reaction in Acid

Development of low cost electrocatalysts with outstanding catalytic activity and stability for oxygen evolution reaction (OER) in acid is a major challenge to produce hydrogen energy from water splitting. Herein, a novel metal‐free electrocatalyst consisting of a oxygen‐functionalized electrochemically exfoliated graphene (OEEG) nanosheets array is reported. Benefitting from a vertically aligned arrays structure and introducing oxygen functional groups, the metal‐free OEEG nanosheets array exhibits superior electrocatalytic activity and stability toward OER with a low overpotential of 334 mV at 10 mA cm^?2 in acidic electrolyte. Such a high OER performance is thus far the best among all previously reported metal‐free carbon‐based materials, and even superior to commercial Ir/C catalysts (420 mV at 10 mA cm^?2) in acid. Characterization results and electrochemical measurements identify the COOH species in the OEEG acting as active sites for acidic OER, which is further supported by atomic‐scale scanning transmission electron microscopy imaging and electron energy‐loss spectroscopy. Density functional theory calculations reveal that the reaction pathway of dual sites that is mixed by zigzag and armchair edges (COOH‐zig‐corner) is better than the pathway of single site.     

TpyCo2+‐Based Coordination Polymers by Water‐Induced Gelling Trigged Efficient Oxygen Evolution Reaction

Though the use of conventional self‐assembled architectures in functional applications involving advanced energy chemistries is an important research area, it remains largely unexplored. The self‐assembly of the threefold and sixfold‐symmetric terpyridines (tpy) with Co(II) salts results in a novel morphological and structural characteristics, regardless of the nature of the self‐assembled fragments. Herein, such metallopolymers are achieved by one‐pot synthesis in CH₃OH/CHCl₃ (v/v = 5:1) mixture ambient. It is found, for the first time, that Co‐containing polymers can be well dispersed in deionized water to form gel‐like self‐assemblies that consist of a highly interconnected 3D network and exhibit enhanced electrical conductivity and thus are attractive as electrocatalysts. As expected, the optimized Co‐based polymeric structures exhibit a low overpotential of 320 mV at 10 mA cm^?2 and high stability over 2000 cycles toward oxygen evolution reaction (OER), surpassing commercial RuO₂/C, single‐site Co catalysts, polymer, and metal–organic framework‐based OER catalysts reported to date. X‐ray absorption spectroscopy and density functional theory calculations reveal that the tpy‐Co²⁺ (3N‐Co or tpy‐Co²⁺) configurations act as highly active sites. Importantly, this work demonstrates the functional application of the self‐assembled metallopolymers as electrocatalysts for energy conversion.     

Hierarchical Porous Ni3S4 with Enriched High‐Valence Ni Sites as a Robust Electrocatalyst for Efficient Oxygen Evolution Reaction

Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) significantly limits the overall energy conversion efficiency of water splitting. In this work, a highly active and stable, meso–macro hierarchical porous Ni₃S₄ architecture, enriched in Ni³⁺ is designed as an advanced electrocatalyst for OER. The obtained Ni₃S₄ architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm^?2 and 300 mV at 50 mA cm^?2. Additionally, this Ni₃S₄ catalyst has excellent long‐term stability (no degradation after 300 h at 50 mA cm^?2). The outstanding OER performance is due to the high concentration of Ni³⁺ and the meso–macro hierarchical porous structure. The presence of Ni³⁺ enhances the chemisorption of OH^?, which facilitates electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water‐splitting electrolyzer using the prepared Ni₃S₄ as the anode catalyst and Pt/C as the cathode catalyst achieves a low cell voltage of 1.51 V at 10 mA cm^?2. Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni³⁺ and hierarchical porous architectures.     

Defect‐Rich Nitrogen Doped Co3O4/C Porous Nanocubes Enable High‐Efficiency Bifunctional Oxygen Electrocatalysis

Heteroatom doping plays a significant role in optimizing the catalytic performance of electrocatalysts. However, research on heteroatom doped electrocatalysts with abundant defects and well‐defined morphology remain a great challenge. Herein, a class of defect‐engineered nitrogen‐doped Co₃O₄ nanoparticles/nitrogen‐doped carbon framework (N‐Co₃O₄@NC) strongly coupled porous nanocubes, made using a zeolitic imidazolate framework‐67 via a controllable N‐doping strategy, is demonstrated for achieving remarkable oxygen evolution reaction (OER) catalysis. X‐ray photoelectron spectroscopy, X‐ray absorption fine structure, and electron spin resonance results clearly reveal the formation of a considerable amount of nitrogen dopants and oxygen vacancies in N‐Co₃O₄@NC. The defect engineering of N‐Co₃O₄@NC makes it exhibit an overpotential of only 266 mV to reach 10 mA cm^?2, a low Tafel slope of 54.9 mV dec^?1 and superior catalytic stability for OER, which is comparable to that of commercial RuO₂. Density functional theory calculations indicate N‐doping could promote catalytic activity via improving electronic conductivity, accelerating reaction kinetics, and optimizing the adsorption energy for intermediates of OER. Interestingly, N‐Co₃O₄@NC also shows a superior oxygen reduction reaction activity, making it a bifunctional electrocatalyst for zinc–air batteries. The zinc–air battery with the N‐Co₃O₄@NC cathode demonstrates superior efficiency and durability, showing the feasibility of N‐Co₃O₄/NC in electrochemical energy devices.     

Ru/Se-RuO2 Composites via Controlled Selenization Strategy for Enhanced Acidic Oxygen Evolution

The introduction of electronegative non-metallic heterostructures is promisingly desired to develop Ru-based oxide catalysts, which have higher activity and robust stability for acidic oxygen evolution reaction (OER). Developing scalable synthetic strategies and enlightening the mechanism understanding of the enhancement is imperative but still challenging. Herein, a facile selenium-assisted reduction approach is reported to fabricate the partially reduced nano-sized Ru with mixed-valence Se species immobilization, directly from commercial RuO₂ through ball milling and annealing procedures. The obtained Ru/Se-RuO₂ composites demonstrate superior electrocatalytic performance toward acidic OER with small overpotentials of 190 and 240 mV at 10 and 100 mA cm⁻², a Tafel slope of only 43.7 mV dec⁻¹, and no detectable activity decay under operation for 24 h. Experimental results further demonstrate a synergistic effect including enhanced electron transfer interaction by the formation of Ru/RuO₂ heterostructures and more available active sites due to Se doping. Theoretical calculations indicate that slight Se doping and metallic Ru loading can significantly decrease the free energy change for the formation of *OOH intermediate, and thus dramatically promotes the OER performance. This strategy offers a promising strategy for the development of non-metallic elements incorporated high-performance catalysts and related water electrocatalytic devices for sustainable energy applications.