Boosting Electrocatalytic Oxygen Evolution over Ce−Co9S8 Core–Shell Nanoneedle Arrays by Electronic and Architectural Dual Engineering

An dual electronic and architectural engineering strategy is a good way to rationally design earth-abundant and highly efficient electrocatalysts of the oxygen evolution reaction (OER) for sustainable hydrogen-based energy devices. Here, a Ce-doped Co₉S₈ core–shell nanoneedle array (Ce−Co₉S₈@CC) supported on a carbon cloth has been designed and developed to accelerate the sluggish kinetics of the OER. Profiting from valance alternative Ce doping, a fine core–shell structure and vertically aligned nanoneedle arrayed architecture, Ce−Co₉S₈@CC integrates modulated electronic structure, highly exposed active sites, and multidimensional mass diffusion channels; together, these afford a favorable catalyzed OER. Ce−Co₉S₈@CC exhibits remarkable performance in the OER in an alkaline medium, where the overpotential requires only 242 mV to deliver a current density of 10 mA cm⁻² for the OER; this is 70 mV superior to that of Ce-free Co₉S₈ catalyst and other counterparts. Good stability and impressive selectivity (nearly 100 % Faradic efficiency) are also demonstrated. When integrated into a two-electrode OER//HER electrolyzer, the as-prepared Ce−Co₉S₈@CC displays a low operation potential of 1.54 V at 10 mA cm⁻² and long-term stability, thus demonstrating great potential for economical water electrolysis.     

Impact of Surface Defects on LaNiO3 Perovskite Electrocatalysts for the Oxygen Evolution Reaction

Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost-effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO₃ perovskite electrocatalysts. Hydrogen reduction of 700 °C calcined LaNiO₃ induces a high density of surface oxygen vacancies, and confers significantly enhanced OER activity and stability compared to unreduced LaNiO₃; the former exhibit a low onset overpotential of 380 mV at 10 mA cm⁻² and a small Tafel slope of 70.8 mV dec⁻¹. Oxygen vacancy formation is accompanied by mixed Ni²⁺/Ni³⁺ valence states, which quantum-chemical DFT calculations reveal modify the perovskite electronic structure. Further, it reveals that the formation of oxygen vacancies is thermodynamically more favourable on the surface than in the bulk; it increases the electronic conductivity of reduced LaNiO₃ in accordance with the enhanced OER activity that is observed.     

NixCo3‐xO4 Nanoneedle Arrays Grown on Ni Foam as an Efficient Bifunctional Electrocatalyst for Full Water Splitting

Developing highly active, stable and robust electrocatalysts based on earth‐abundant elements for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is important for many renewable energy conversion processes. Herein, Ni_xCo_3‐xO₄ nanoneedle arrays grown on 3D porous nickel foam (NF) was synthesized as a bifunctional electrocatalyst with OER and HER activity for full water splitting. Benefiting from the advantageous structure, the composite exhibits superior OER activity with an overpotential of 320 mV achieving the current density of 10 mA cm^?2. An exceptional HER activity is also acquired with an overpotential of 170 mV at the current density of 10 mA cm^?2. Furthermore, the catalyst also shows the superior activity and stability for 20 h when used in the overall water splitting cell. Thus, the hierarchical 3D structure composed of the 1D nanoneedle structure in Ni_xCo_3‐xO₄/NF represents an avenue to design and develop highly active and bifunctional electrocatalysts for promising energy conversion.     

Cooperative Ni(Co)-Ru-P Sites Activate Dehydrogenation for Hydrazine Oxidation Assisting Self-powered H2 Production

Water electrolysis for H₂ production is restricted by the sluggish oxygen evolution reaction (OER). Using the thermodynamically more favorable hydrazine oxidation reaction (HzOR) to replace OER has attracted ever-growing attention. Herein, we report a twisted NiCoP nanowire array immobilized with Ru single atoms (Ru₁−NiCoP) as superior bifunctional electrocatalyst toward both HzOR and hydrogen evolution reaction (HER), realizing an ultralow working potential of −60 mV and overpotential of 32 mV for a current density of 10 mA cm⁻², respectively. Inspiringly, two-electrode electrolyzer based on overall hydrazine splitting (OHzS) demonstrates outstanding activity with a record-high current density of 522 mA cm⁻² at cell voltage of 0.3 V. DFT calculations elucidate the cooperative Ni(Co)−Ru−P sites in Ru₁−NiCoP optimize H* adsorption, and enhance adsorption of *N₂H₂ to significantly lower the energy barrier for hydrazine dehydrogenation. Moreover, a self-powered H₂ production system utilizing OHzS device driven by direct hydrazine fuel cell (DHzFC) achieve a satisfactory rate of 24.0 mol h⁻¹ m⁻².     

Hollow Nanotube Ru/Cu2+1O Supported on Copper Foam as a Bifunctional Catalyst for Overall Water Splitting

Hydrogen energy is considered as one of the ideal clean energies for solving the energy shortage and environmental issues, and developing highly efficient electrocatalysts for overall water splitting to produce hydrogen is still a huge challenge. Herein, for the first time, Ru-doped Cu₂₊₁O vertically arranged nanotube arrays in situ grown on Cu foam (Ru/Cu₂₊₁O NT/CuF) are reported and further investigated for their catalytic properties for overall water splitting. The Ru/Cu₂₊₁O NT/CuF presents ultrahigh catalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions, and it exhibits a small overpotential of 32 mV at 10 mA cm⁻² in the HER, and only needs 210 mV overpotential to achieve a current density of 10 mA cm⁻² in the OER. Importantly, the alkaline electrolyzer using Ru/Cu₂₊₁O NT/CuF as a bifunctional electrocatalyst only needs 1.53 V voltage to deliver a current density of 10 mA cm⁻², which is much lower than the benchmark of IrO₂(+)/Pt(−) counterpart (1.64 V at 10 mA cm⁻²). The excellent performance of the Ru/Cu₂₊₁O NT/CuF catalyst is attributed to its high conductive substrate and special Ru-doped nanotube structure, which provides a high electrochemical active surface area and 3D gas diffusion channel.     

Electrodeposition at Highly Negative Potentials of an Iron-Cobalt Oxide Catalyst for Use in Electrochemical Water Splitting

Earth-abundant transition metal-based catalysts have been extensively investigated for their applicability in water electrolysers to enable overall water splitting to produce clean hydrogen and oxygen. In this study a Fe−Co based catalyst is electrodeposited in 30 seconds under vigorous hydrogen evolution conditions to produce a high surface area material that is active for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). This catalyst can achieve high current densities of 600 mAcm⁻² at an applied potential of 1.6 V (vs RHE) in 1 M NaOH with a Tafel slope value of 48 mV dec⁻¹ for the OER. In addition, the HER can be facilitated at current densities as high as 400 mA cm⁻² due to the large surface area of the material. The materials were found to be predominantly amorphous but did contain crystalline regions of CoFe₂O₄ which became more evident after the OER indicating interesting compositional and structural changes that occur to the catalyst after an electrocatalytic reaction. This rapid method of creating a bimetallic oxide electrode for both the HER and OER could possibly be adopted to other bimetallic oxide systems suitable for electrochemical water splitting.     

Atmospheric-Temperature Chain Reaction towards Ultrathin Non-Crystal-Phase Construction for Highly Efficient Water Splitting

Combining the self-sacrifice of a highly crystalline substance to design a multistep chain reaction towards ultrathin active-layer construction for high-performance water splitting with atmospheric-temperature conditions and an environmentally benign aqueous environment is extremely intriguing and full of challenges. Here, taking cobalt carbonate hydroxides (CCHs) as the initial crystalline material, we choose the Lewis acid metal salt of Fe(NO₃)₃ to induce an aqueous-phase chain reaction generating free CO₃²⁻ ions with subsequent instant FeCO₃ hydrolysis. The resultant ultrathin (∼5 nm) amorphous Fe-based hydroxide layer on CCH results in considerable activity in catalyzing the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), yielding 10/50 mA ⋅ cm⁻² at overpotentials of 230/266.5 mV for OER and 72.5/197.5 mV for HER. The catalysts can operate constantly in 1.0 M KOH over 48 and 45 h for the OER and HER, respectively. For bifunctional catalysis for alkaline electrolyzer assembly, a cell voltage as low as 1.53 V was necessary to yield 10 mA cm⁻² (1.7 V at 50 mA cm⁻²). This work rationally builds high-efficiency electrochemical bifunctional water-splitting catalysts and offers a trial in establishing a controllable nanolevel ultrathin lattice disorder layer through an atmospheric-temperature chemical route.     

Improving the Electrocatalytic Activity of a Nickel-Organic Framework toward the Oxygen Evolution Reaction through Vanadium Doping

Metal-organic frameworks (MOFs) have been considered as potential oxygen evolution reaction (OER) electrocatalysts owning to their ultra-thin structure, adjustable composition, high surface area, and high porosity. Here, we designed and fabricated a vanadium-doped nickel organic framework (V_1−x−Ni_xMOF) system by using a facile two-step solvothermal method on nickel foam (NF). The doping of vanadium remarkably elevates the OER activity of V_1−x−Ni_xMOF, thus demonstrating better performance than the corresponding single metallic Ni-MOF, NiV-MOF and RuO₂ catalysts at high current density (>400 mA cm⁻²). V_0.09−Ni_0.91MOF/NF provides a low overpotential of 235 mV and a small Tafel slope of 30.3 mV dec⁻¹ at a current density of 10 mA cm⁻². More importantly, a water-splitting device assembled with Pt/C/NF and V_0.09−Ni_0.91MOF/NF as cathode and anode yielded a cell voltage of 1.96 V@1000 mA cm⁻², thereby outperforming the-state-of-the-art RuO₂⁽⁺⁾||Pt/C⁽⁻⁾. Our work sheds new insight on preparing stable, efficient OER electrocatalysts and a promising method for designing various MOF-based materials.     

Controlled Synthesis of 3D Flower‐like Ni2P Composed of Mesoporous Nanoplates for Overall Water Splitting

Developing efficient non‐noble metal and earth‐abundant electrocatalysts with tunable microstructures for overall water splitting is critical to promote clean energy technologies for a hydrogen economy. Herein, novel three‐dimensional (3D) flower‐like Ni₂P composed of mesoporous nanoplates with controllable morphology and high surface area was prepared by a hydrothermal method and low‐temperature phosphidation as efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Compared with the urchin‐like Ni_x P_y , the 3D flower‐like Ni₂P with a diameter of 5 μm presented an efficient and stable catalytic performance in 0.5 m H₂SO₄, with a small Tafel slope of 79 mV dec⁻¹ and an overpotential of about 240 mV at a current density of 10 mA cm⁻² with a mass loading density of 0.283 mg cm⁻². In addition, the catalyst also exhibited a remarkable performance for the OER in 1.0 m KOH electrolyte, with an overpotential of 320 mV to reach a current density of 10 mA cm⁻² and a small Tafel slope of 72 mV dec⁻¹. The excellent catalytic performance of the as‐prepared Ni₂P may be ascribed to its novel 3D morphology with unique mesoporous structure.     

Synchronous Electrocatalytic Design of Architectural and Electronic Structure Based on Bifunctional LDH-Co3O4/NF toward Water Splitting

The rational design of highly efficient bifunctional electrocatalysts for water splitting is extremely urgent for application in sustainable energy conversion processes to alleviate the energy crisis and environmental pollution. In this work, through simple deposition of layered double hydroxides (LDH) on Co₃O₄/NF (NF=nickel foam) nanosheets arrays, hierarchical Co³⁺-rich materials based on LDH-Co₃O₄/NF are prepared as highly active and stable electrocatalysts for water splitting. The NiFe-LDH-Co₃O₄/NF demonstrates excellent electrochemical activity with an overpotential of 214 mV for the OER and an overpotential of 162 mV for the HER at 10 mA cm⁻². Such a performance is attributed to the optimized electronic states with a high concentration of Co³⁺, which improves the intrinsic activity, and the sheet-on-sheet hierarchical structure, which increases the number of active sites. The unique synchronous design of both the architectural and electronic structure of nanomaterials can simultaneously accelerate the reaction kinetics and provide a more convenient charge transfer path. Therefore, the strategy reported herein may open a new pathway for the design of excellent electrocatalysts for water splitting.     

Co−Co Dinuclear Active Sites Dispersed on Zirconium-doped Heterostructured Co9S8/Co3O4 for High-current-density and Durable Acidic Oxygen Evolution

Developing cost-effective and sustainable acidic water oxidation catalysts requires significant advances in material design and in-depth mechanism understanding for proton exchange membrane water electrolysis. Herein, we developed a single atom regulatory strategy to construct Co−Co dinuclear active sites (DASs) catalysts that atomically dispersed zirconium doped Co₉S₈/Co₃O₄ heterostructure. The X-ray absorption fine structure elucidated the incorporation of Zr greatly facilitated the generation of Co−Co DASs layer with stretching of cobalt oxygen bond and S−Co−O heterogeneous grain boundaries interfaces, engineering attractive activity of significantly reduced overpotential of 75 mV at 10 mA cm⁻², a breakthrough of 500 mA cm⁻² high current density, and water splitting stability of 500 hours in acid, making it one of the best-performing acid-stable OER non-noble metal materials. The optimized catalyst with interatomic Co−Co distance (ca. 2.80 Å) followed oxo-oxo coupling mechanism that involved obvious oxygen bridges on dinuclear Co sites (1,090 cm⁻¹), confirmed by in situ SR-FTIR, XAFS and theoretical simulations. Furthermore, a major breakthrough of 120,000 mA g⁻¹ high mass current density using the first reported noble metal-free cobalt anode catalyst of Co−Co DASs/ZCC in PEM-WE at 2.14 V was recorded.     

Imine Gels Based on Ferrocene and Porphyrin and Their Electrocatalytic Property

A series of porphyrin‐based imine gels have been synthesized via dynamic covalent gelation between 5,10,15,20‐tetra(4‐aminophenyl)‐21H,23H‐porphyrin (H₂TAPP) derivatives and various aldehyde compounds. The porphyrin‐ferrocene imine gels based on MTAPP (M=H₂, Ni²⁺, Co²⁺, Pd²⁺ and Zn²⁺) and ferrocene‐1,1′‐dicarbaldehyde (NA) display efficient HER, OER and ORR activities in alkaline media. Among the gels, CoTAPP‐NA shows an HER current density of 10 mA cm^?2 at low overpotential of 470 mV and small Tafel slope of 110 mV decade^?1 in alkaline media. CoTAPP‐NA also exhibits OER catalytic activity with low overpotential (416 mV for 10 mA cm^?2). CoTAPP‐NA shows ability in overall water splitting in alkaline media. In addition, CoTAPP‐NA exhibits onset potential (E_p) of 0.95 V and half‐wave potential (E_1/2) of 0.84 V in 1.0 mol L^?1 KOH solution for oxygen reduction. Moreover, the gel catalyst shows good stability.     

Constructing RuCoOx/NC Nanosheets with Low Crystallinity within ZIF-9 as Bifunctional Catalysts for Highly Efficient Overall Water Splitting

Electrocatalysts play a pivotal role in accelerating the sluggish electrochemical water splitting reaction. Herein, a Ru−Co oxides and carbon nitrides hybrid (RuCoO_x/NC) electrocatalyst was constructed by employing ZIF-9 to disperse Ru precursor and deliberately regulating the calcination temperature. The moderate calcination temperature results in the RuCoO_x nanocomposites with small particle size and low crystallinity as well as the co-existence of multi-valence metal compounds, thus boosting the amount and species of active sites. Moreover, the strong interactions between Co and Ru species induce the electron transfer from Co to Ru, thus enhancing the adsorption of anion intermediates on the electron-deficient Co species and the proton capturing capacity of electron-sufficient Ru species. As a result, the optimized RuCoO_x/NC-350 catalyst behaved good electrocatalytic activities with 73 and 210 mV overpotential to achieve 10 mA cm⁻² for HER and OER, respectively. Remarkably, it showed good durability by holding at 100 mA cm⁻² for 100 h in HER and 50 mA cm⁻² for 24 h in OER with small activity decline. This study may shed new light on the rational construction of highly efficient Ru-based catalysts for electrochemical water splitting.     

Magnetic Field-Enhanced Electrocatalytic Oxygen Evolution on a Mixed-Valent Cobalt-Modulated LaCoO3 Catalyst

Extensive efforts to enhance the oxygen evolution reaction (OER) catalytic performance of transition metal oxides mainly concentrate on the extrinsic morphology tailoring, lattice doping, and electrode interface optimizing. Nevertheless, little room is left for performance improvement using these methods and an obvious gap still exists compared to the precious metal catalysts. In this work, a novel “mixed-valent cobalt modulation” strategy is presented to enhance the electrocatalytic OER of perovskite LaCoO₃ (LCO) oxide. The valence transition of cobalt is realized by ethylenediamine post reduction procedure at room temperature, which further induces the variation of magnetic properties for LCO catalyst. The optimized LCO catalyst with Co²⁺/Co³⁺ of 1.98 % exhibits the best OER activity, and the overpotential at 10 mA cm⁻² current density is decreased by 170 mV compared pristine LCO. Impressively, the ferromagnetic LCO catalyst can perform magnetic OER enhancement. By application of an external magnetic field, the overpotential of LCO at 10 mA cm⁻² can be further decreased by 20 mV compared to that of under zero magnetic field, which arises from the enhanced energy states of electrons and accelerated electron transfer process driven by magnetic field. Our findings may provide a promising strategy to break the bottleneck for further enhancement of OER performance.     

Two-Dimensional NiIr@N-Doped Carbon Nanocomposites Supported on Ni Foam for Electrocatalytic Overall Water Splitting

Electrochemical water splitting can provide a promising avenue for sustainable hydrogen production. Highly efficient electrocatalysts toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are extremely important for the practical application of water splitting technology. Herein, a one-step annealing strategy is reported for the fabrication of a metal–organic framework-derived bifunctional self-supported electrocatalyst, which is composed of two-dimensional N-doped carbon-wrapped Ir-doped Ni nanoparticle composites supported on Ni foam (NiIr@N-C/NF). The resultant NiIr@N-C/NF displays excellent electrocatalytic performance in 1.0 m KOH, with low overpotentials of 32 mV at 10 mA cm⁻² for the HER and 329 mV at 50 mA cm⁻² for the OER. Particularly, the HER-OER bifunctional NiIr@N-C/NF needs only 1.50 V to yield 10 mA cm⁻² for overall water splitting.     

Boosting electrochemical hydrogen evolution by coupling anodically oxidative dehydrogenation of benzylamine to benzonitrile

The electricity-driven water splitting acts as a promising pathway for renewable energy conversion and storage, yet anodic oxygen evolution reaction (OER) largely hinders its efficiency. Seeking the alternatives to OER exhibits the competitive advance to address this predicament. In this work, we show a more thermodynamically and kinetically favorable reaction, electrochemical oxidative dehydrogenation (EODH) of benzylamine to replace the conventional OER, catalyzed by a cobalt cyclotetraphosphate (Co₂P₄O₁₂) nanorods catalyst grown on nickel foam. This anodic reaction lowers the electricity input of 317 mV toward the desired current density of 100 mA/cm², together with a highly selective benzonitrile product of more than 97%. More specifically, when coupling it with cathodic hydrogen evolution reaction (HER), the proposed HER||benzylamine-EODH configuration only requires a cell voltage of 1.47 V@100 mA/cm², exhibiting an energy-saving up to 17% relative to conventional water splitting, as well as the near unit selectivity toward cathodic H₂ and anodic benzonitrile products.     

Ru-Doping Enhanced Electrocatalysis of Metal–Organic Framework Nanosheets toward Overall Water Splitting

An Ru-doping strategy is reported to substantially improve both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activity of Ni/Fe-based metal–organic framework (MOF) for overall water splitting. As-synthesized Ru-doped Ni/Fe MIL-53 MOF nanosheets grown on nickel foam (MIL-53(Ru-NiFe)@NF) afford HER and OER current density of 50 mA cm⁻² at an overpotential of 62 and 210 mV, respectively, in alkaline solution with a nominal Ru loading of ≈110 μg cm⁻². When using as both anodic and cathodic (pre-)catalyst, MIL-53(Ru-NiFe)@NF enables overall water splitting at a current density of 50 mA cm⁻² for a cell voltage of 1.6 V without iR compensation, which is much superior to state-of-the-art RuO₂-Pt/C-based electrolyzer. It is discovered that the Ru-doping considerably modulates the growth of MOF to form thin nanosheets, and enhances the intrinsic HER electrocatalytic activity by accelerating the sluggish Volmer step and improving the intermediate oxygen adsorption for increased OER catalytic activity.     

Controlled Synthesis of Cr‐Co0.85Se Nanoarrays for Water Splitting at an Ultralow Cell Voltage of 1.43 V

Water splitting has attracted more and more attention as a promising strategy for the production of clean hydrogen fuel. In this work, a new synthesis strategy was proposed, and Co_0.85Se was synthesized on nickel foam as the main matrix. The doping of appropriate Cr amount into the target of Co_0.85Se and the Cr‐Co_0.85Se resulted in an excellent electrochemical performance. The doping of Cr introduces Cr³⁺ ions which substitute Co²⁺ and Co³⁺ ions in Co_0.85Se, so that the lattice parameters of the main matrix were changed. It is worth noting that the Cr0.15‐Co_0.85Se/NF material exhibits an excellent performance in the oxygen evolution reaction (OER) test. When the current density reaches 50 mA cm^?2 for OER, the overpotential is only 240 mV. For the hydrogen evolution reaction (HER) tests, the overpotential is only 117 mV to drive 10 mA cm^?2 of current density. Moreover, when the Cr0.15‐Co_0.85Se/NF material is used as a two‐electrode device for whole water splitting, the required cell voltage is only 1.43 V to reach a current density of 10 mA cm^?2, which is among the lowest values of the published catalysts up to now. In addition, the Cr0.15‐Co_0.85Se/NF catalyst also exhibits excellent stability during a long period of water splitting. The experimental result demonstrates that the change of the lattice structure has an obvious influence on the electrocatalytic activity of the material. When an external electric field is applied, it facilitates the rapid electron transfer rate and enhances the electrocatalytic performance and stability of the material.     

From a Molecular 2Fe‐2Se Precursor to a Highly Efficient Iron Diselenide Electrocatalyst for Overall Water Splitting

A highly active FeSe₂ electrocatalyst for durable overall water splitting was prepared from a molecular 2Fe‐2Se precursor. The as‐synthesized FeSe₂ was electrophoretically deposited on nickel foam and applied to the oxygen and hydrogen evolution reactions (OER and HER, respectively) in alkaline media. When used as an oxygen‐evolution electrode, a low 245 mV overpotential was achieved at a current density of 10 mA cm⁻², representing outstanding catalytic activity and stability because of Fe(OH)₂/FeOOH active sites formed at the surface of FeSe₂. Remarkably, the system is also favorable for the HER. Moreover, an overall water‐splitting setup was fabricated using a two‐electrode cell, which displayed a low cell voltage and high stability. In summary, the first iron selenide material is reported that can be used as a bifunctional electrocatalyst for the OER and HER, as well as overall water splitting.     

Bimetallic cobalt-nickel coordination polymer electrocatalysts for enhancing oxygen evolution reaction

Coordination polymers（CPs） have great potential to be used in electrocatalysis owing to their designable compositions and structures. It is highly challenging to apply CPs as electrocatalysts for oxygen evolution reaction（OER） on account of insufficient catalytic efficiency and relatively poor stability of current electrocatalysts. Herein, through a mixed-metal strategy, one-dimensional Co_xNi_1-x-HIPA with dual active sites was synthesized and studied for OER electrocatalyst...