Electronic and Vacancy Engineering of Mo–RuCoOx Nanoarrays for High-Efficiency Water Splitting (Adv. Funct. Mater. 40/2023)

Exploring efficient strategies to achieve novel high-efficiency catalysts for water splitting is of great significance to develop hydrogen energy technology. Herein, unique molybdenum (Mo)-doped ruthenium–cobalt oxide (Mo–RuCoO_x) nanosheet arrays are prepared as a high-performance bifunctional electrocatalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through combining electronic and vacancy engineering. Theoretical calculations and experimental results reveal that the incorporation of Ru and Mo can effectively tune the electronic structure, and the controllable Mo dissolution coupling with the oxygen vacancy generation during surface reconstruction is able to optimize the adsorption energy of hydrogen/oxygen intermediates, thus greatly accelerating the kinetics for both HER and OER. As a result, the Mo–RuCoO_x nanoarrays exhibit remarkably low overpotentials of 41 and 156 mV at 10 mA cm⁻² for HER and OER in 1 m KOH, respectively. Furthermore, the two-electrode electrolyzer assembled by the Mo–RuCoO_x nanoarrays requires a cell voltage as low as 1.457 V to achieve 10 mA cm⁻² for alkaline overall water splitting. This work holds great promise to develop novel and highly active electrocatalysts for future energy conversion applications.     

Mo-/Co-N-C Hybrid Nanosheets Oriented on Hierarchical Nanoporous Cu as Versatile Electrocatalysts for Efficient Water Splitting

Designing robust and cost-effective electrocatalysts based on Earth-abundant elements is crucial for large-scale hydrogen production through electrochemical water splitting. Here, nitrogen-doped carbon engrafted Mo₂N/CoN hybrid nanosheets that are seamlessly oriented on hierarchical nanoporous Cu scaffold (Mo-/Co-N-C/Cu), as highly efficient electrocatalysts for alkaline hydrogen evolution reaction are reported. The constituent heterostructured Mo₂N/CoN nanosheets work as bifunctional electroactive sites for both water dissociation and adsorption/desorption of hydrogen intermediates while the nitrogen-doped carbon bridges electron transfers between electroactive sites and interconnective Cu current collectors by making use of Mo-/Co-N-C bonds and intimate C/Cu contacts at interfaces. As a consequence of unique architecture having electroactive sites to be sufficiently accessible, self-supported nanoporous Mo-/Co-N-C/Cu hybrid electrodes exhibit outstanding electrocatalysis in 1 m KOH, with a negligible onset overpotential and a low Tafel slope of 47 mV dec⁻¹. They only take overpotential of as low as 230 mV to reach current density of 1000 mA cm⁻². When coupled with their electro-oxidized derivatives that mediate efficiently the oxygen evolution reaction, the alkaline water electrolyzer can achieve ≈100 mA cm⁻² at 1.622 V in 1 m KOH electrolyte, ≈0.343 V lower than the device constructed with commercially available Pt/C and Ir/C nanocatalysts immobilized on nanoporous Cu electrodes.     

Single-Atom Co-Decorated MoS2 Nanosheets Assembled on Metal Nitride Nanorod Arrays as an Efficient Bifunctional Electrocatalyst for pH-Universal Water Splitting

The commercialization of electrochemical water splitting technology requires electrocatalysts that are cost-effective, highly efficient, and stable. Herein, an advanced bifunctional electrocatalyst based on single-atom Co-decorated MoS₂ nanosheets grown on 3D titanium nitride (TiN) nanorod arrays (CoSAs-MoS₂/TiN NRs) has been developed for overall water splitting in pH-universal electrolytes. When applied as a self-standing cathodic electrode, the CoSAs-MoS₂/TiN NRs requires overpotentials of 187.5, 131.9, and 203.4 mV to reach a HER current density of 10 mA cm^–2 in acidic, alkaline, and neutral conditions, respectively, which are superior to the most previously reported non-noble metal HER electrocatalysts at the same current density. The CoSAs-MoS₂/TiN NRs anodic electrode also shows low OER overpotentials of 454.9, 340.6, and 508.0 mV, respectively, at a current density of 10 mA cm^–2 in acidic, alkaline, and neutral mediums, markedly outperforming current OER catalysts reported elsewhere. More importantly, an electrolyzer delivered from the cathodic and anodic CoSAs-MoS₂/TiN NRs electrodes exhibits an extraordinary overall water splitting performance with good stability and durability in pH-universal conditions.     

Ni3N–CeO2 Heterostructure Bifunctional Catalysts for Electrochemical Water Splitting

Developing low-cost and high-efficient bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is greatly significant for water electrolysis. Here, Ni₃N-CeO₂/NF heterostructure is synthesized on the nickel foam, and it exhibits excellent HER and OER performance. As a result, the water electrolyzer based on Ni₃N-CeO₂/NF bifunctional catalyst only needs 1.515 V@10 mA cm⁻², significantly better than that of Pt/C||IrO₂ catalysts. In situ characterizations unveil that CeO₂ plays completely different roles in HER and OER processes. In situ infrared spectroscopy and density functional theory calculations indicate that the introduction of CeO₂ can optimizes the structure of interface water, and the synergistic effect of Ni₃N and CeO₂ improve the HER activity significantly, while the in situ Raman spectra reveal that CeO₂ accelerates the reconstruction of O_V (oxygen vacancy)-rich NiOOH for boosting OER. This study clearly unlocks the different catalytic mechanisms of CeO₂ for boosting the HER and OER activity of Ni₃N for water splitting, which provides the useful guidance for designing the high-performance bifunctional catalysts for water splitting.     

Realizing the Synergy of Interface Engineering and Chemical Substitution for Ni3N Enables its Bifunctionality Toward Hydrazine Oxidation Assisted Energy-Saving Hydrogen Production

Hydrazine oxidation assisted water electrolysis offers a unique rationale for energy-saving hydrogen production, yet the lack of effective non-noble-metal bifunctional catalysts is still a grand challenge at the current stage. Here, the Mo doped Ni₃N and Ni heterostructure porous nanosheets grow on Ni foam (denoted as Mo Ni₃N/Ni/NF) are successfully constructed, featuring simultaneous interface engineering and chemical substitution, which endow the outstanding bifunctional electrocatalytic performances toward both hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER), demanding a working potential of −0.3 mV to reach 10 mA cm⁻² for HzOR and −45 mV for that of HER. Impressively, the overall hydrazine splitting (OHzS) system requires an ultralow cell voltage of 55 mV to deliver 10 mA cm⁻² with remarkable long-term durability. Moreover, as a proof-of-concept, economical H₂ production systems utilizing OHzS unit powered by a waste AAA battery, a commercial solar cell, and a homemade direct hydrazine fuel cell (DHzFC) are investigated to inspire future practical applications. The density functional theory calculations demonstrate that the synergy of Mo substitution and abundant Ni₃N/Ni interface owns a more thermoneutral value for H* absorption ability toward HER and optimized dehydrogenation process for HzOR.     

Engineering Active Iron Sites on Nanoporous Bimetal Phosphide/Nitride Heterostructure Array Enabling Robust Overall Water Splitting

Alkaline water electrolysis is a commercially viable technology for green H₂ production using renewable electricity from intermittent solar or wind energy, but very few non-noble bifunctional catalysts simultaneously exhibit superb catalytic efficiency and stability at large current densities for hydrogen and oxygen evolution reactions (HER and OER, respectively), especially for iron-based catalysts. Given that iron is the most abundant and least expensive transition metal, iron-based compounds are very attractive low-cost targets as active electrocatalysts for bifunctional water splitting with large-current durability. Herein, the in situ construction of a self-supported Fe₂P/Co₂N porous heterostructure arrays possessing superb bifunctional catalytic activity in base is reported, featured by low overpotentials of 131 and 283 mV to attain a current density of 500 mA cm⁻² for HER and OER, respectively, outperforming most of non-noble bifunctional electrocatalysts reported hitherto. Particularly, this hybrid catalyst also displays an excellent overall water splitting activity, requiring low voltages of 1.561 and 1.663 V to attain 100 and 500 mA cm⁻² with excellent durability in 1 m KOH, respectively. Most importantly, the catalyst is stable for >120 h, even when the current density is 500 mA cm⁻², which is prominently superior to IrO₂⁽⁺⁾//Pt⁽⁻⁾ coupled noble electrodes, and is among the very best bifunctional catalysts reported thus far. Detailed theoretical calculations reveal that the interfacial interaction between Fe₂P and Co₂N can further improve the H* binding energy at the iron sites.     

Interfacial Engineering of Nickel Hydroxide on Cobalt Phosphide for Alkaline Water Electrocatalysis

Catalysts based on earth-abundant non-noble metals are interesting candidates for alkaline water electrolysis in sustainable hydrogen economies. However, such catalysts often suffer from high overpotential and sluggish kinetics in both the hydrogen and oxygen evolution reactions (HER and OER). In this study, a hybrid catalyst made of iron-doped cobalt phosphide (Fe-CoP) nanowire arrays and Ni(OH)₂ nanosheets is introduced that displays strong electronic interactions at the interface, which significantly improves the interfacial reactivity of reactants and/or intermediates with the hybrid catalyst surface. The combined experimental and theoretical study further confirms that the hybrid catalyst promotes the sluggish rate-limiting steps in both the HER and OER. Full water electrolysis is thus enabled to take place at such a low cell voltage as 1.52 V to reach the current density of 10 mA cm⁻² along with superior durability and high conversion efficiency.     

Bifunctional Porous NiFe/NiCo2O4/Ni Foam Electrodes with Triple Hierarchy and Double Synergies for Efficient Whole Cell Water Splitting

A 3D hierarchical porous catalyst architecture based on earth abundant metals Ni, Fe, and Co has been fabricated through a facile hydrothermal and electrodeposition method for efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The electrode is comprised of three levels of porous structures including the bottom supermacroporous Ni foam (≈500 μm) substrate, the intermediate layer of vertically aligned macroporous NiCo₂O₄ nanoflakes (≈500 nm), and the topmost NiFe(oxy)hydroxide mesoporous nanosheets (≈5 nm). This hierarchical architecture is binder‐free and beneficial for exposing catalytic active sites, enhancing mass transport and accelerating dissipation of gases generated during water electrolysis. Serving as an anode catalyst, the designed hierarchical electrode displays excellent OER catalytic activity with an overpotential of 340 mV to achieve a high current density of 1200 mA cm^?2. Serving as a cathode catalyst, the catalyst exhibits excellent performance toward HER with a moderate overpotential of 105 mV to deliver a current density of 10 mA cm^?2. Serving as both anode and cathode catalysts in a two‐electrode water electrolysis system, the designed electrode only requires a potential of 1.67 V to deliver a current density of 10 mA cm^?2 and exhibits excellent durability in prolonged bulk alkaline water electrolysis.     

Rapid Synthesis of Various Electrocatalysts on Ni Foam Using a Universal and Facile Induction Heating Method for Efficient Water Splitting

Electrocatalytic water splitting for the production of hydrogen proves to be effective and available. In general, the thermal radiation synthesis usually involves a slow heating and cooling process. Here, a high-frequency induction heating (IH) is employed to rapidly prepare various self-supported electrocatalysts grown on Ni foam (NF) in liquid- and gas-phase within 1–3 min. The NF not only serves as an in situ heating medium, but also as a growth substrate. The as-synthesized Ni nanoparticles anchored on MoO₂ nanowires supported on NF (Ni-MoO₂/NF-IH) enable catalysis of hydrogen evolution reaction (HER), showing a low overpotential of −39 mV (10 mA cm⁻²) and maintaining the stability of 12 h in alkaline condition. Moreover, the NiFe layered double hydroxide (NiFe LDH/NF-IH) is also synthesized via IH and affords outstanding oxygen evolution reaction (OER) activity with an overpotential of 246 mV (10 mA cm⁻²). The Ni-MoO₂/NF-IH and NiFe LDH/NF-IH are assembled to construct a two-electrode system, where a small cell voltage of ≈1.50 V enables a current density of 10 mA cm⁻². More importantly, this IH method is also available to rapidly synthesize other freestanding electrocatalysts on NF, such as transition metal hydroxides and metal nitrides.     

Etching‐Doping Sedimentation Equilibrium Strategy: Accelerating Kinetics on Hollow Rh‐Doped CoFe‐Layered Double Hydroxides for Water Splitting

Exploring highly active and inexpensive bifunctional electrocatalysts for water‐splitting is considered to be one of the prerequisites for developing hydrogen energy technology. Here, an efficient simultaneous etching‐doping sedimentation equilibrium (EDSE) strategy is proposed to design and prepare hollow Rh‐doped CoFe‐layered double hydroxides for overall water splitting. The elaborate electrocatalyst with optimized composition and typical hollow structure accelerates the electrochemical reactions, which can achieve a current density of 10 mA cm^?2 at an overpotential of 28 mV (600 mA cm^?2 at 188 mV) for hydrogen evolution reaction (HER) and 100 mA cm^?2 at 245 mV for oxygen evolution reaction (OER). The cell voltage for overall water splitting of the electrolyzer assembled by this electrocatalyst is only 1.46 V, a value far lower than that of commercial electrolyzer constructed by Pt/C and RuO₂ and most reported bifunctional electrocatalysts. Furthermore, the existence of Fe vacancies introduced by Rh doping and the typical hollow structure are demonstrated to optimize the entire HER and OER processes. EDSE associates doping with template‐directed hollow structures and paves a new avenue for developing bifunctional electrocatalysts for overall water splitting. It is also believed to be practical in other catalysis fields as well.     

Sub-2 nm Ultrathin and Robust 2D FeNi Layered Double Hydroxide Nanosheets Packed with 1D FeNi-MOFs for Enhanced Oxygen Evolution Electrocatalysis

Water oxidation is a critical process for electrochemical water splitting due to its inherent sluggish kinetics. In spite of the high catalytic activities of noble metal-based electrocatalysts for water oxidation, their high cost, rare reserves, and low stabilities drive researchers to exploit efficient but low-cost electrocatalysts. Ultrathin 2D nanomaterials are considered efficient electrocatalysts for oxygen evolution reaction (OER) in water splitting. Herein, a facile strategy is proposed to fabricate 2D FeNi layered double hydroxide (FeNi-LDH) nanosheets packed with the in situ produced 1D sword-like FeNi-MOFs by using FeNi-LDH as a semi-sacrificial template. In the composite, the thickness of the formed nanosheets is only 1.34 nm, much thinner than that of most previously reported 2D materials. The 1D porous sword-like MOF nanorods have a long length of around 1.3 µm. Due to the unique 2D/1D combined structure, the as-prepared FeNi LDH/MOF is directly used as electrocatalyst for the OER displays enhanced OER electrocatalytic performance with a low overpotential of 272 mV@100 mA cm^–2, a small Tafel slope of 34.1 mV dec^–1, high long-term durability. This work provides a new way to fabricate integrated ultrathin 2D nanosheets and MOFs as advanced catalysts for electrochemical energy conversion.     

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.     

3D Self‐Supported Fe‐Doped Ni2P Nanosheet Arrays as Bifunctional Catalysts for Overall Water Splitting

The development of highly efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for improving the efficiency of overall water splitting, but still remains challenging issue. Herein, 3D self‐supported Fe‐doped Ni₂P nanosheet arrays are synthesized on Ni foam by hydrothermal method followed by in situ phosphorization, which serve as bifunctional electrocatalysts for overall water splitting. The as‐synthesized (Ni_0.33Fe_0.67)₂P with moderate Fe doping shows an outstanding OER performance, which only requires an overpotential of ≈230 mV to reach 50 mA cm^?2 and is more efficient than the other Fe incorporated Ni₂P electrodes. In addition, the (Ni_0.33Fe_0.67)₂P exhibits excellent activity toward HER with a small overpotential of ≈214 mV to reach 50 mA cm^?2. Furthermore, an alkaline electrolyzer is measured using (Ni_0.33Fe_0.67)₂P electrodes as cathode and anode, respectively, which requires cell voltage of 1.49 V to reach 10 mA cm^?2 as well as shows excellent stability with good nanoarray construction. Such good performance is attributed to the high intrinsic activity and superaerophobic surface property.     

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.     

Sub-2 nm Thiophosphate Nanosheets with Heteroatom Doping for Enhanced Oxygen Electrocatalysis

Developing an efficient bifunctional electrocatalyst with accelerated kinetics is important but challenging for rechargeable metal-air batteries. In this study, a series of anion-regulated sub-2 nm ultrathin thiophosphate nanosheets (NiPS_3–xSe_x NSs) is rationally designed and synthesized as bifunctional oxygen evolution/reduction reaction (OER/ORR) electrocatalysts for Zn-air batteries. The increase of nominal Se dopants (0 ≤ x ≤ 0.5) leads to the expansion of (001) crystal plane spacing and partially disordered structure generation after the incorporation of Se to pristine NiPS₃. More importantly, electronic structures of active sites can be reasonably regulated via coordination of the interaction between anions and cations. Density functional theory calculations reveal that such tailored electronic structures reduce the overpotential of the thermodynamic barriers step for both OER and ORR as well as shorten energy bandgap, which can accelerate reaction kinetics in electrocatalytic processes and enhance electrical conductivity. Consequently, the obtained NiPS_3–xSe_x NSs exhibit low OER overpotential (250 mV) and positive ORR onset potential (0.94 V), large power density (152 mW cm⁻²), and robust stability (96 h cycle) for Zn-air devices, far exceeding that of precious metal catalysts. This study provides a novel tactic to design earth-abundant and highly efficient bifunctional electrocatalysts for metal-air battery technologies.     

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.     

Regulating the Electronic Structure of CoP Nanosheets by O Incorporation for High‐Efficiency Electrochemical Overall Water Splitting

The exploration of earth‐abundant and high‐efficiency bifunctional electrocatalysts for overall water splitting is of vital importance for the future of the hydrogen economy. Regulation of electronic structure through heteroatom doping represents one of the most powerful strategies to boost the electrocatalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a rational design of O‐incorporated CoP (denoted as O‐CoP) nanosheets, which synergistically integrate the favorable thermodynamics through modification of electronic structures with accelerated kinetics through nanostructuring, is reported. Experimental results and density functional theory simulations manifest that the appropriate O incorporation into CoP can dramatically modulate the electronic structure of CoP and alter the adsorption free energies of reaction intermediates, thus promoting the HER and OER activities. Specifically, the optimized O‐CoP nanosheets exhibit efficient bifunctional performance in alkaline electrolyte, requiring overpotentials of 98 and 310 mV to deliver a current density of 10 mA cm^?2 for HER and OER, respectively. When served as bifunctional electrocatalysts for overall water splitting, a low cell voltage of 1.60 V is needed for achieving a current density of 10 mA cm^?2. This proposed anion‐doping strategy will bring new inspiration to boost the electrocatalytic performance of transition metal–based electrocatalysts for energy conversion applications.     

Large‐Size,Porous, Ultrathin NiCoP Nanosheets for Efficient Electro/Photocatalytic Water Splitting

Porous ultrathin 2D catalysts are attracting great attention in the field of electro/photocatalytic hydrogen evolution reaction (HER) and overall water splitting. Herein, a universal pH‐controlled wet‐chemical strategy is reported followed by thermal and phosphorization treatment to prepare large‐size, porous and ultrathin bimetallic phosphide (NiCoP) nanosheets, in which graphene oxide is adopted as a template to determine the size of products. The thickness of the resultant NiCoP nanosheets ranges from 3.5 to 12.8 nm via delicately adjusting pH from 7.8 to 8.5. The thickness‐dependent electrocatalytic performance is evidenced experimentally and explained by computational studies. The prepared large‐size ultrathin NiCoP nanosheets show excellent bifunctional electrocatalytic activity for overall water splitting, with low overpotentials of 34.3 mV for HER and 245.0 mV for oxygen evolution reaction, respectively, at 10 mA cm^?2. Furthermore, the NiCoP nanosheets exhibit superior photocatalytic HER performance, achieving a high HER rate of 238.2 mmol h^?1 g^?1 in combination with commonly used photocatalyst CdS, which is far superior to that of Pt/CdS (81.7 mmol h^?1 g^?1). All these results demonstrate large‐size porous ultrathin NiCoP nanosheets as an efficient and multifunctional electro/photocatalyst for water splitting.     

Ag Anchored Atomically Around Nanopores of Porous Co(OH)2 for Efficient Bifunctional Oxygen Catalysis

Various clean energy storage and conversion systems highly depend on rational design of efficient electrocatalysts for oxygen reactions. Increasing both gas molecular diffusion and intrinsic activity is critical to boosting its efficiency for bifunctional oxygen electrocatalysis. However, controllable synthesis of catalysts that combines gas molecular diffusion and intrinsic activity remains a fundamental challenge. Herein, a two-step synthetic strategy is adopted to fabricate a composite oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalyst (P-Ag-Co(OH)₂), of which, atomic Ag is anchored in reactive oxygen atoms around nanopores of Co(OH)₂ nanosheets. Abundant nanopores provide enough gas molecular diffusion channels, and the special Ag-O-Co-OH catalytic groups around nanopores display high intrinsic catalytic activity, which jointly result in an excellent ORR/OER performance. In alkaline electrolyte, P-Ag-Co(OH)₂ displays a high half-wave potential (0.902 V versus RHE) for ORR, and a low overpotential (235 mV at 10 mA cm⁻²) for OER, which is superior to non-noble catalysts in previous studies and Pt/C (Ir/C) catalyst. At the same time, the single-cell zinc-air battery is prepared with an extremely high discharge peak power density of 435 mW cm⁻² and excellent discharge–charge cycle stability.     

Hexagonal Defect-Rich MnOx/RuO2 with Abundant Heterointerface to Modulate Electronic Structure for Acidic Oxygen Evolution Reaction

Developing green hydrogen energy to power future societies has driven the progress of proton-exchange membrane water electrolyzers (PEMWE). However, due to the complex anode oxygen evolution reaction (OER) electron transfer process and the strong acidic environment, the most effective catalysts are still Ir-based nanomaterials. Therefore, exploiting low cost acidic OER catalysts to meet the needs of PEMWE remains a challenging and rewarding task. Herein, hexagonal-shaped and defect-rich MnO_x/RuO₂ heterojunction nanosheets (H/d-MnO_x/RuO₂) is designed. The oxygen vacancies and heterogeneous structure enable the H/d-MnO_x/RuO₂ catalyst to reach 10 mA cm⁻² with only overpotential 178 mV in 0.5 m H₂SO₄. Density functional theory shows that the oxygen vacancies and heterogeneous interface facilitates the reduction of the adsorption energy of *OOH and the reduction of the energy level of Ru-Oads, thus suppressing the involvement of lattice oxygen and enhancing the durability. This study provides an effective way to design efficient catalysts for hydrogen production in PEMWE.