Reduced Graphene Oxide‐Wrapped Co9–xFexS8/Co,Fe‐N‐C Composite as Bifunctional Electrocatalyst for Oxygen Reduction and Evolution

Searching for highly efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) using nonnoble metal‐based catalysts is essential for the development of many energy conversion systems, including rechargeable fuel cells and metal–air batteries. Here, Co_9–xFe_xS₈/Co,Fe‐N‐C hybrids wrapped by reduced graphene oxide (rGO) (abbreviated as S‐Co_9–xFe_xS₈@rGO) are synthesized through a semivulcanization and calcination method using graphene oxide (GO) wrapped bimetallic zeolite imidazolate framework (ZIF) Co,Fe‐ZIF (CoFe‐ZIF@GO) as precursors. Benefiting from the synergistic effect of OER active CoFeS and ORR active Co,Fe‐N‐C in a single component, as well as high dispersity and enhanced conductivity derived from rGO coating and Fe‐doping, the obtained S‐Co_9–xFe_xS₈@rGO‐10 catalyst shows an ultrasmall overpotential of ≈0.29 V at 10 mA cm^?2 in OER and a half‐wave potential of 0.84 V in ORR, combining a superior oxygen electrode activity of ≈0.68 V in 0.1 m KOH.     

Active Sites Intercalated Ultrathin Carbon Sheath on Nanowire Arrays as Integrated Core–Shell Architecture: Highly Efficient and Durable Electrocatalysts for Overall Water Splitting

The development of active bifunctional electrocatalysts with low cost and earth‐abundance toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a great challenge for overall water splitting. Herein, metallic Ni₄Mo nanoalloys are firstly implanted on the surface of NiMoO_x nanowires array (NiMo/NiMoO_x ) as metal/metal oxides hybrid. Inspired by the superiority of carbon conductivity, an ultrathin nitrogen‐doped carbon sheath intercalated NiMo/NiMoO_x (NC/NiMo/NiMoO_x ) nanowires as integrated core–shell architecture are constructed. The integrated NC/NiMo/NiMoO_x array exhibits an overpotential of 29 mV at 10 mA cm^?2 and a low Tafel slope of 46 mV dec^?1 for HER due to the abundant active sites, fast electron transport, low charge‐transfer resistance, unique architectural structure and synergistic effect of carbon sheath, nanoalloys, and oxides. Moreover, as OER catalysts, the NC/NiMo/NiMoO_x hybrids require an overpotential of 284 mV at 10 mA cm^?2. More importantly, the NC/NiMo/NiMoO_x array as a highly active and stable electrocatalyst approaches ≈10 mA cm^?2 at a voltage of 1.57 V, opening an avenue to the rational design and fabrication of the promising electrode materials with architecture structures toward the electrochemical energy storage and conversion.     

Hierarchically Porous Co/CoxMy (M = P,N) as an Efficient Mott–Schottky Electrocatalyst for Oxygen Evolution in Rechargeable Zn–Air Batteries

Tailoring composition and morphology of electrocatalysts is of great importance in improving their catalytic performance. Herein, a salt‐templated strategy is proposed to construct novel multicomponent Co/Co_xM_y (M = P, N) hybrids with outstanding electrocatalytic performance for the oxygen evolution reaction (OER). The obtained Co/Co_xM_y hybrids present porous sheet‐like architecture consisting of many hierarchical secondary building‐units. The synthetic strategy depends on a facile and effective dissolution–recrystallization–pyrolysis process under NH₃ atmosphere of the precursors, which does not involve any surfactant or long‐time hydrothermal pretreatment. That is different from the conventional methods for the synthesis of hierarchical nitrides/phosphides. Benefitting from unique composition/structure‐dependent merits, the Co/Co_xM_y hybrids as a typical Mott–Schottky electrocatalyst exhibit good OER performance in an alkaline medium compared with their counterparts, as evidenced by a low overpotential of 334 mV at 10 mA cm^?2 and a small Tafel slope of 79.2 mV dec^?1, as well as superior long‐term stability. More importantly, the Co/Co_xM_y+Pt/C achieves higher voltaic efficiency and several times longer cycle life than conventional RuO₂+Pt/C catalysts in rechargeable Zn–air batteries. It is envisioned that the present work can provide a new avenue for the development of Mott–Schottky electrocatalysts for sustainable energy storage.     

Co9S8 Nanoparticles‐Embedded N/S‐Codoped Carbon Nanofibers Derived from Metal–Organic Framework‐Wrapped CdS Nanowires for Efficient Oxygen Evolution Reaction

Metal–organic frameworks (MOFs) with tunable compositions and morphologies are recognized as efficient self‐sacrificial templates to achieve function‐oriented nanostructured materials. Moreover, it is urgently needed to develop highly efficient noble metal‐free oxygen evolution reaction (OER) electrocatalysts to accelerate the development of overall water splitting green energy conversion systems. Herein, a facile and cost‐efficient strategy to synthesize Co₉S₈ nanoparticles‐embedded N/S‐codoped carbon nanofibers (Co₉S₈/NSCNFs) as highly active OER catalyst is developed. The hybrid precursor of core–shell ZIF‐wrapped CdS nanowires is first prepared and then leads to the formation of uniformly dispersed Co₉S₈/N, S‐codoped carbon nanocomposites through a one‐step calcination reaction. The optimal Co₉S₈/NSCNFs‐850 is demonstrated to possess excellent electrocatalytic performance for OER in 1.0 m KOH solution, affording a low overpotential of 302 mV to reach the current density of 10 mA cm^?2, a small Tafel slope of 54 mV dec^?1, and superior long‐term stability for 1000 cyclic voltammetry cycles. The favorable results raise a concept of exploring more MOF‐based nanohybrids as precursors to induce the synthesis of novel porous nanomaterials as non‐noble‐metal electrocatalysts for sustainable energy conversion.     

Constructing Pure Phase Tungsten‐Based Bimetallic Carbide Nanosheet as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Carbides are commonly regarded as efficient hydrogen evolution reaction (HER) catalysts, but their poor oxygen evolution reaction (OER) catalytic activities seriously limit their practical application in overall water splitting. Here, vertically aligned porous cobalt tungsten carbide nanosheet embedded in N‐doped carbon matrix (Co₆W₆C@NC) is successfully constructed on flexible carbon cloth (CC) as an efficient bifunctional electrocatalyst for overall water splitting via a facile metal–organic framework (MOF) derived method. The synergistic effect of Co and W atoms effectively tailors the electron state of carbide, optimizing the hydrogen‐binding energy. Thus Co₆W₆C@NC shows an enhanced HER performance with an overpotential of 59 mV at a current density of ?10 mA cm^?2. Besides, Co₆W₆C@NC easily in situ transforms into tungsten actived cobalt oxide/hydroxide during the OER process, serving as OER active species, which provides an excellent OER activity with an overpotential of 286 mV at a current density of ?10 mA cm^?2. The water splitting device, by applying Co₆W₆C@NC as both the cathode and anode, requires a low cell voltage of 1.585 V at 10 mA cm^?2 with the great stability in alkaline solution. This work provides a feasible strategy to fabricate bimetallic carbides and explores their possibility as bifunctional catalysts toward overall water splitting.     

Amorphous Bimetallic Oxide–Graphene Hybrids as Bifunctional Oxygen Electrocatalysts for Rechargeable Zn–Air Batteries

Metal oxides of earth‐abundant elements are promising electrocatalysts to overcome the sluggish oxygen evolution and oxygen reduction reaction (OER/ORR) in many electrochemical energy‐conversion devices. However, it is difficult to control their catalytic activity precisely. Here, a general three‐stage synthesis strategy is described to produce a family of hybrid materials comprising amorphous bimetallic oxide nanoparticles anchored on N‐doped reduced graphene oxide with simultaneous control of nanoparticle elemental composition, size, and crystallinity. Amorphous Fe_0.5Co_0.5O_x is obtained from Prussian blue analog nanocrystals, showing excellent OER activity with a Tafel slope of 30.1 mV dec^?1 and an overpotential of 257 mV for 10 mA cm^?2 and superior ORR activity with a large limiting current density of ?5.25 mA cm^?2 at 0.6 V. A fabricated Zn–air battery delivers a specific capacity of 756 mA h g_Zn^?1 (corresponding to an energy density of 904 W h kg_Zn^?1), a peak power density of 86 mW cm^?2 and can be cycled over 120 h at 10 mA cm^?2. Other two amorphous bimetallic, Ni_0.4Fe_0.6O_x and Ni_0.33Co_0.67O_x , are also produced to demonstrate the general applicability of this method for synthesizing binary metal oxides with controllable structures as electrocatalysts for energy conversion.     

3D Architectures of CoxP Using Silk Fibroin Scaffolds: An Active and Stable Electrocatalyst for Hydrogen Generation in Acidic and Alkaline Media

Developing nonprecious, highly active, and stable catalysts is essential for efficient electrocatalytic hydrogen evolution reaction in water splitting. In this study, the facile synthesis of a 3D flower‐like Co_xP/carbon architecture is proposed composed of an assembly of nanosheets interconnected by silk fibroin that acts as 3D scaffolds and a carbon source. This unique 3D architecture coupled with a carbon matrix enhances catalytic activity by exposing more active sites and increasing charge transport. The flower‐like Co_xP/carbon can facilitate a lower overpotential, Tafel slope, charge transfer resistance, and a higher electrochemically active surface than carbon‐free and silk‐free Co_xP. The nanostructured architecture exhibits excellent catalytic performance with low overpotentials of 109 and 121 mV at 10 mA cm^?2 and Tafel slopes of 55 and 62 mV dec^?1 in acidic and alkaline media, respectively. Furthermore, it minimally degrades the overpotential and current density after long‐term stability tests 10 000 cyclic voltammetry cycles and a chronoamperometric test over 40 h, respectively, in acidic media, which confirms the high durability and stability of the flower‐like Co_xP/carbon.     

Chemical Valence‐Dependent Electrocatalytic Activity for Oxygen Evolution Reaction: A Case of Nickel Sulfides Hybridized with N and S Co‐Doped Carbon Nanoparticles

Exploration of the relationship between electrocatalytic activities and their chemical valence is very important in rational design of high‐efficient electrocatalysts. A series of porous nickel sulfides hybridized with N and S co‐doped carbon nanoparticles (Ni_xS_y‐NSCs) with different chemical valences of Ni, Ni₉S₈‐NSCs, Ni₉S₈‐NiS_1.03‐NSCs, and NiS_1.03‐NSCs are successfully fabricated, and their electrocatalytic performances as oxygen evolution reaction electrocatalysts are systematically investigated. The Ni_xS_y‐NSCs are obtained via a two‐step reaction including a low‐temperature synthesis of Ni‐Cys precursor followed by thermal decomposing of the precursor in Ar atmosphere. By controlling the sulfidation process during the formation of Ni_xS_y‐NSCs, Ni₉S₈‐NSCs, Ni₉S₈‐NiS_1.03‐NSCs, and NiS_1.03‐NSCs are obtained, respectively, giving rise to the increase of high‐valence Ni component, and resulting in gradually enhanced oxygen evolution reaction electrocatalytic activities. In particular, the NiS_1.03‐NSCs show an exceptional low overpotential of ≈270 mV versus reversible hydrogen electrode at a current density of 10 mA cm^?2 and a small Tafel slope of 68.9 mV dec^?1 with mass loading of 0.25 mg cm^?2 in 1 m KOH and their catalytic activities remained for at least 10 h, which surpass the state‐of‐the‐art IrO₂, RuO₂, and Ni‐based electrocatalysts.     

Graphene Composites with Cobalt Sulfide: Efficient Trifunctional Electrocatalysts for Oxygen Reversible Catalysis and Hydrogen Production in the Same Electrolyte

Nitrogen and sulfur‐codoped graphene composites with Co₉S₈ (NS/rGO‐Co) are synthesized by facile thermal annealing of graphene oxides with cobalt nitrate and thiourea in an ammonium atmosphere. Significantly, in 0.1 m KOH aqueous solution the best sample exhibits an oxygen evolution reaction (OER) activity that is superior to that of benchmark RuO₂ catalysts, an oxygen reduction reaction (ORR) activity that is comparable to that of commercial Pt/C, and an overpotential of only ?0.193 V to reach 10 mA cm^?2 for hydrogen evolution reaction (HER). With this single catalyst for oxygen reversible electrocatalysis, a potential difference of only 0.700 V is observed in 0.1 m KOH solution between the half‐wave potential in ORR and the potential to reach 10 mA cm^?2 in OER; in addition, an overpotential of only 450 mV is needed to reach 10 mA cm^?2 for full water splitting in the same electrolyte. The present trifunctional catalytic activities are markedly better than leading results reported in recent literature, where the remarkable trifunctional activity is attributed to the synergetic effects between N,S‐codoped rGO, and Co₉S₈ nanoparticles. These results highlight the significance of deliberate structural engineering in the preparation of multifunctional electrocatalysts for versatile electrochemical reactions.     

Synergism of Geometric Construction and Electronic Regulation: 3D Se‐(NiCo)Sx/(OH)x Nanosheets for Highly Efficient Overall Water Splitting

The exploration of highly efficient electrocatalysts for both oxygen and hydrogen generation via water splitting is receiving considerable attention in recent decades. Up till now, Pt‐based catalysts still exhibit the best hydrogen evolution reaction (HER) performance and Ir/Ru‐based oxides are identified as the benchmark for oxygen evolution reaction (OER). However, the high cost and rarity of these materials extremely hinder their large‐scale applications. This paper describes the construction of the ultrathin defect‐enriched 3D Se‐(NiCo)S_x/(OH)_x nanosheets for overall water splitting through a facile Se‐induced hydrothermal treatment. Via Se‐induced fabrication, highly efficient Se‐(NiCo)S_x/(OH)_x nanosheets are successfully fabricated through morphology optimization, defect engineering, and electronic structure tailoring. The as‐prepared hybrids exhibit relatively low overpotentials of 155 and 103 mV at the current density of 10 mA cm^?2 for OER and HER, respectively. Moreover, an overall water‐splitting device delivers a current density of 10 mA cm^?2 for ≈66 h without obvious degradation.     

Ultrathin Iron‐Cobalt Oxide Nanosheets with Abundant Oxygen Vacancies for the Oxygen Evolution Reaction

Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H₂ fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H₂ production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low‐cost fabrication route. Herein, a facile solution reduction method using NaBH₄ as a reductant is developed to prepare iron‐cobalt oxide nanosheets (Fe_x Co_y ‐ONSs) with a large specific surface area (up to 261.1 m² g^?1), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe₁Co₁‐ONS measured at an overpotential of 350 mV reaches up to 54.9 A g^?1, while its Tafel slope is 36.8 mV dec^?1; both of which are superior to those of commercial RuO₂, crystalline Fe₁Co₁‐ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe₁Co₁‐ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH^? ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H₂O onto nearby Co³⁺ sites.     

Super‐Exchange Interaction Induced Overall Optimization in Ferromagnetic Perovskite Oxides Enables Ultrafast Water Oxidation

Oxygen evolution reaction (OER) is crucial in many renewable electrochemical technologies including regenerative fuel cells, rechargeable metal–air batteries, and water splitting. It is found that abundant active sites with favorable electronic structure and high electrical conductivity play a dominant role in achieving high electrocatalytic efficiency of perovskites, thus efficient strategies need to be designed to generate multiple beneficial factors for OER. Here, highlighted is an unusual super‐exchange effect in ferromagnetic perovskite oxide to optimize active sites and enhance electrical conductivity. A systematic exploration about the composition‐dependent OER activity in SrCo_1x Ru_x O_3?δ (denoted as SCRx) (x = 0.0–1.0) perovskite is displayed with special attention on the role of super‐exchange interaction between high spin (HS) Co³⁺ and Ru⁵⁺ ions. Induced by the unique Co³⁺–O–Ru⁵⁺ super‐exchange interactions, the SCR0.1 is endowed with abundant OER active species including Co³⁺/Co⁴⁺, Ru⁵⁺, and O₂^2?/O^?, high electrical conductivity, and metal–oxygen covalency. Benefiting from these advantageous factors for OER electrocatalysis, the optimized SCR0.1 catalyst exhibits a remarkable activity with a low overpotential of 360 mV at 10 mA cm^?2, which exceeds the benchmark RuO₂ and most well‐known perovskite oxides reported so far, while maintaining excellent durability. This work provides a new pathway in developing perovskite catalysts for efficient catalysis.     

Strain Regulation to Optimize the Acidic Water Oxidation Performance of Atomic‐Layer IrOx

Strain regulation has become an important strategy to tune the surface chemistry and optimize the catalytic performance of nanocatalysts. Herein, the construction of atomic‐layer IrO_x on IrCo nanodendrites with tunable Ir? O bond length by compressive strain effect for oxygen evolution reaction (OER) in acidic environment is demonstrated. Evidenced from in situ extended X‐ray absorption fine structure, it is shown that the compressive strain of the IrO_x layer on the IrCo nanodendrites decreases gradually from 2.51% to the unstrained state with atomic layer growth (from ≈2 to ≈9 atomic layers of IrO_x), resulting in the variation of the Ir? O bond length from shortened 1.94 Å to normal 1.99 Å. The ≈3 atomic‐layer IrO_x on IrCo nanodendrites with an Ir? O bond length of 1.96 Å (1.51% strain) exhibits the optimal OER activity compared to the higher‐strained (2.51%, ≈2 atomic‐layer IrO_x) and unstrained (>6 atomic‐layer IrO_x) counterparts, with an overpotential of only 247 mV to achieve a current density of 10 mA cm^?2. Density functional theory calculations reveal that the precisely tuned compressive strain effect balances the adsorbate–substrate interaction and facilitates the rate‐determining step to form HOO*, thus assuring the best performance of the three atomic‐layer IrO_x for OER.     

Nitrogen‐Doped Graphene‐Encapsulated Nickel–Copper Alloy Nanoflower for Highly Efficient Electrochemical Hydrogen Evolution Reaction

Development of high‐performance and low‐cost nonprecious metal electrocatalysts is critical for eco‐friendly hydrogen production through electrolysis. Herein, a novel nanoflower‐like electrocatalyst comprising few‐layer nitrogen‐doped graphene‐encapsulated nickel–copper alloy directly on a porous nitrogen‐doped graphic carbon framework (denoted as Ni_x Cu_y @ NG‐NC) is successfully synthesized using a facile and scalable method through calcinating the carbon, copper, and nickel hydroxy carbonate composite under inert atmosphere. The introduction of Cu can effectively modulate the morphologies and hydrogen evolution reaction (HER) performance. Moreover, the calcination temperature is an important factor to tune the thickness of graphene layers of the Ni_x Cu_y @ NG‐NC composites and the associated electrocatalytic performance. Due to the collective effects including unique porous flowered architecture and the synergetic effect between the bimetallic alloy core and graphene shell, the Ni₃Cu₁@ NG‐NC electrocatalyst obtained under optimized conditions exhibits highly efficient and ultrastable activity toward HER in harsh environments, i.e., a low overpotential of 122 mV to achieve a current density of 10 mA cm^?2 with a low Tafel slope of 84.2 mV dec^?1 in alkaline media, and a low overpotential of 95 mV to achieve a current density of 10 mA cm^?2 with a low Tafel slope of 77.1 mV dec^?1 in acidic electrolyte.     

Edge Sites with Unsaturated Coordination on Core–Shell Mn3O4@MnxCo3−xO4 Nanostructures for Electrocatalytic Water Oxidation

Transition‐metal oxides are extensively investigated as efficient electrocatalysts for the oxygen evolution reaction (OER). However, large‐scale applications remain challenging due to their moderate catalytic activity. Optimized regulation of surface states can lead to improvement of catalytic properties. Here, the design of Mn@Co_x Mn_3?x O₄ nanoparticles with abundant edge sites via a simple seed‐mediated growth strategy is described. The unsaturated coordination generated on the edge sites of Co_x Mn_3?x O₄ shells makes a positive contribution to the surface‐structure tailoring. Density functional theory calculations indicate that the edge sites with unsaturated coordination exhibit intense affinity for OH^? in the alkaline electrolyte, which greatly enhances the electrochemical OER performance of the catalysts. The resulting Mn@Co_x Mn_3?x O₄ catalysts yield a current density of 10 mA cm^?2 at an overpotential of 246 mV and a relatively low Tafel slope of 46 mV dec^?1. The successful synthesis of these metal oxides nanoparticles with edge sites may pave a new path for rationally fabricating efficient OER catalysts.     

Hierarchical 3D Oxygenated Cobalt Molybdenum Selenide Nanosheets as Robust Trifunctional Catalyst for Water Splitting and Zinc–Air Batteries

The development of hierarchical nanostructures with highly active and durable multifunctional catalysts has a new significance in the context of new energy technologies of water splitting and metal–air batteries. Herein, a strategy is demonstrated to construct a 3D hierarchical oxygenated cobalt molybdenum selenide (O‐Co_1?xMo_xSe₂) series with attractive nanoarchitectures, which are fabricated by a simple and cost‐effective hydrothermal process followed by an exclusive ion‐exchange process. Owing to its highly electroactive sites with numerous nanoporous networks and plentiful oxygen vacancies, the optimal O‐Co_0.5Mo_0.5Se₂ could catalyze the hydrogen evolution reaction and oxygen evolution reaction effectively with a low overpotential of ≈102 and 189 mV, at a current density of 10 mA cm^?2, respectively, and exceptional durability. Most importantly, the O‐Co_0.5Mo_0.5Se₂||O‐Co_0.5Mo_0.5Se₂ water splitting device only entails a voltage of ≈1.53 V at a current density of 10 mA cm^?2, which is much better than benchmark Pt/C||RuO₂ (≈1.56 V). Furthermore, O‐Co_0.5Mo_0.5Se₂ air cathode‐based zinc–air batteries exhibit an excellent power density of 120.28 mW cm^?2 and exceptional cycling stability for 60 h, superior to those of state‐of‐art Pt/C+RuO₂ pair‐based zinc–air batteries. The present study provides a strategy to design hierarchical 3D oxygenated bimetallic selenide‐based multifunctional catalysts for energy conversion and storage systems.     

Sulfur‐Modified Graphitic Carbon Nitride Nanostructures as an Efficient Electrocatalyst for Water Oxidation

There is an urgent need to develop metal‐free, low cost, durable, and highly efficient catalysts for industrially important oxygen evolution reactions. Inspired by natural geodes, unique melamine nanogeodes are successfully synthesized using hydrothermal process. Sulfur‐modified graphitic carbon nitride (S‐modified g‐CN _x ) electrocatalysts are obtained by annealing these melamine nanogeodes in situ with sulfur. The sulfur modification in the g‐CN _x structure leads to excellent oxygen evolution reaction activity by lowering the overpotential. Compared with the previously reported nonmetallic systems and well‐established metallic catalysts, the S‐modified g‐CN _x nanostructures show superior performance, requiring a lower overpotential (290 mV) to achieve a current density of 10 mA cm^?2 and a Tafel slope of 120 mV dec^?1 with long‐term durability of 91.2% retention for 18 h. These inexpensive, environmentally friendly, and easy‐to‐synthesize catalysts with extraordinary performance will have a high impact in the field of oxygen evolution reaction electrocatalysis.     

In situ growth of Co3O4 nanoneedles on titanium mesh for electrocatalytic oxygen evolution

Designing high-efficient and low cost of electrodes with seamless integration of substrate and electrocatalyst particles is of significant concern for electrocatalytic water splitting. In this study, we actualized in situ growth of Co₃O₄ nanoneedles on titanium (Ti) mesh (denoted as Co₃O₄@Ti) by a simple combination of hydrothermal approach and subsequently calcination treatment under relatively low temperatures. The as-prepared Co₃O₄@Ti samples were evaluated as anodes for electrocatalytic oxygen evolution reaction (OER) in alkaline electrolyte. It demonstrates that the optimized Co₃O₄@Ti electrode displayed good OER activity with a small overpotential of 416 mV at a current density of 20 mA cm^?2, which is on a par with commercial RuO₂ catalyst (overpotential of 403 mV at 20 mA cm^?2). The satisfactory OER performance of Co₃O₄@Ti electrode is largely attributed to the seamless integration of conductive Ti mesh substrate and the direct growth of Co₃O₄ nanoneedles on Ti mesh with sufficient active sites. This study suggests the potential application of Co₃O₄@Ti electrode as preeminent OER catalyst.

     

Exceptional Performance of Hierarchical Ni–Fe (hydr)oxide@NiCu Electrocatalysts for Water Splitting

Developing low‐cost bifunctional electrocatalysts with superior activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of great importance for the widespread application of the water splitting technique. In this work, using earth‐abundant transition metals (i.e., nickel, iron, and copper), 3D hierarchical nanoarchitectures, consisting of ultrathin Ni–Fe layered‐double‐hydroxide (Ni–Fe LDH) nanosheets or porous Ni–Fe oxides (NiFeO_x) assembled to a metallic NiCu alloy, are delicately constructed. In alkaline solution, the as‐prepared Ni–Fe LDH@NiCu possesses outstanding OER activity, achieving a current density of 10 mA cm^?2 at an overpotential of 218 mV, which is smaller than that of RuO₂ catalyst (249 mV). In contrast, the resulting NiFeO_x@NiCu exhibits better HER activity, yielding a current density of 10 mA cm^?2 at an overpotential of 66 mV, which is slightly higher than that of Pt catalyst (53 mV) but superior to all other transition metal (hydr)oxide‐based electrocatalysts. The remarkable activity of the Ni–Fe LDH@NiCu and NiFeO_x@NiCu is further demonstrated by a 1.5 V solar‐panel‐powered electrolyzer, resulting in current densities of 10 and 50 mA cm^?2 at overpotentials of 293 and 506 mV, respectively. Such performance renders the as‐prepared materials as the best bifunctional electrocatalysts so far.     

Ultrafine Co3O4 Nanoparticles within Nitrogen‐Doped Carbon Matrix Derived from Metal–Organic Complex for Boosting Lithium Storage and Oxygen Evolution Reaction

Transition metal oxides have recently received great attention for application in advanced lithium‐ion batteries (LIBs) and oxygen evolution reaction (OER). Herein, the ethylenediaminetetraacetic cobalt complex as a precursor to synthesize ultrafine Co₃O₄ nanoparticles encapsulated into a nitrogen‐doped carbon matrix (NC) composites is presented. The as‐prepared Co₃O₄/NC‐350 obtained by pyrolysis at 350 °C demonstrates superior rate performance (372 mAh g^?1 at 5.0 A g^?1) and high cycling stability (92% capacity retention after 300 cycles at 1.0 A g^?1) as anode for LIBs. When evaluated as an electrocatalyst for OER, the Co₃O₄/NC‐350 achieves an overpotential of 298 mV at a current density of 10 mA cm^?2. The NC‐encapsualted porous hierarchical structure assures fast and continuous electron transportation, high activity sites, and strong structural integrity. This works offers novel complex precursors for synthesizing transition metal–based electrodes for boosting electrochemical energy conversion and storage.