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Given that the oxygen evolution reaction (OER) faces challenges due to its sluggish kinetics, development of efficient and robust OER catalytic electrodes is critical for reducing the cost of hydrogen production through electrochemical water splitting. In this study, a biphasic CoNi/Zn(Fe,Al,Cr)2O4 coating, characterized by a densely organized stalagmite‐like microarray structure, is deposited on a commercial pure titanium plate, creating an exceptionally effective OER catalytic electrode. The formation of numerous metal/spinel oxide heterogeneous interfaces is demonstrated to enhance its electron transfer ability and conductivity. At high potentials, aluminum leaching and lattice oxygen consumption can facilitate deep surface reconstruction of highly active Fe‐doped CoNiOOH phase inducing electrochemical activation, further optimizing thermodynamic barrier of the fundamental reaction step. Ultimately, this electrode showcases exceptional OER catalytic performance (low overpotential of 248 and 335 mV to deliver the current density of 10 and 100 mA cm−2) compared to commercial IrO2 catalyst (overpotential of ≈310 mV at 10 mA cm−2). Moreover, it demonstrates high current stability sustaining a current density of 500 mA cm−2 for 100 h. This work deepens the comprehension of the surface reconstruction process in OER and, more broadly, introduces a new avenue for designing and enhancing the performance of catalytic materials. [ABSTRACT FROM AUTHOR]

Modulating the microenvironment of single‐atom catalysts (SACs) is critical to optimizing catalytic activity. Herein, we innovatively propose a strategy to improve the local reaction environment of Ru single atoms by precisely switching the crystallinity of the support from high crystalline and low crystalline, which significantly improves the hydrogen evolution reaction (HER) activity. The Ru single‐atom catalyst anchored on low‐crystalline nickel hydroxide (Ru−LC−Ni(OH)2) reconstructs the distribution balance of the interfacial ions due to the activation effect of metal dangling bonds on the support. Single‐site Ru with a low oxidation state induces the aggregation of hydronium ions (H3O+), leading to the formation of a local acidic microenvironment in alkaline media, breaking the pH‐dependent HER activity. As a comparison, the Ru single‐atom catalyst anchored on high‐crystalline nickel hydroxide (Ru−HC−Ni(OH)2) exhibits a sluggish Volmer step and a conventional local reaction environment. As expected, Ru−LC−Ni(OH)2 requires low overpotentials of 9 and 136 mV at 10 and 1000 mA cm−2 in alkaline conditions and operates stably at 500 mA cm−2 for 500 h in an alkaline seawater anion exchange membrane (AEM) electrolyzer. This study provides a new perspective for constructing highly active single‐atom electrocatalysts. [ABSTRACT FROM AUTHOR]

Modulating the microenvironment of single‐atom catalysts (SACs) is critical to optimizing catalytic activity. Herein, we innovatively propose a strategy to improve the local reaction environment of Ru single atoms by precisely switching the crystallinity of the support from high crystalline and low crystalline, which significantly improves the hydrogen evolution reaction (HER) activity. The Ru single‐atom catalyst anchored on low‐crystalline nickel hydroxide (Ru−LC−Ni(OH)2) reconstructs the distribution balance of the interfacial ions due to the activation effect of metal dangling bonds on the support. Single‐site Ru with a low oxidation state induces the aggregation of hydronium ions (H3O+), leading to the formation of a local acidic microenvironment in alkaline media, breaking the pH‐dependent HER activity. As a comparison, the Ru single‐atom catalyst anchored on high‐crystalline nickel hydroxide (Ru−HC−Ni(OH)2) exhibits a sluggish Volmer step and a conventional local reaction environment. As expected, Ru−LC−Ni(OH)2 requires low overpotentials of 9 and 136 mV at 10 and 1000 mA cm−2 in alkaline conditions and operates stably at 500 mA cm−2 for 500 h in an alkaline seawater anion exchange membrane (AEM) electrolyzer. This study provides a new perspective for constructing highly active single‐atom electrocatalysts. [ABSTRACT FROM AUTHOR]

Designing novel single‐atom catalysts (SACs) supports to modulate the electronic structure is crucial to optimize the catalytic activity, but rather challenging. Herein, a general strategy is proposed to utilize the metalloid properties of supports to trap and stabilize single‐atoms with low‐valence states. A series of single‐atoms supported on the surface of tungsten carbide (M‐WCx, M=Ru, Ir, Pd) are rationally developed through a facile pyrolysis method. Benefiting from the metalloid properties of WCx, the single‐atoms exhibit weak coordination with surface W and C atoms, resulting in the formation of low‐valence active centers similar to metals. The unique metal‐metal interaction effectively stabilizes the low‐valence single atoms on the WCx surface and improves the electronic orbital energy level distribution of the active sites. As expected, the representative Ru‐WCx exhibits superior mass activities of 7.84 and 62.52 A mgRu−1 for the hydrogen oxidation and evolution reactions (HOR/HER), respectively. In‐depth mechanistic analysis demonstrates that an ideal dual‐sites cooperative mechanism achieves a suitable adsorption balance of Had and OHad, resulting in an energetically favorable Volmer step. This work offers new guidance for the precise construction of highly active SACs. [ABSTRACT FROM AUTHOR]

Designing novel single‐atom catalysts (SACs) supports to modulate the electronic structure is crucial to optimize the catalytic activity, but rather challenging. Herein, a general strategy is proposed to utilize the metalloid properties of supports to trap and stabilize single‐atoms with low‐valence states. A series of single‐atoms supported on the surface of tungsten carbide (M‐WCx, M=Ru, Ir, Pd) are rationally developed through a facile pyrolysis method. Benefiting from the metalloid properties of WCx, the single‐atoms exhibit weak coordination with surface W and C atoms, resulting in the formation of low‐valence active centers similar to metals. The unique metal‐metal interaction effectively stabilizes the low‐valence single atoms on the WCx surface and improves the electronic orbital energy level distribution of the active sites. As expected, the representative Ru‐WCx exhibits superior mass activities of 7.84 and 62.52 A mgRu−1 for the hydrogen oxidation and evolution reactions (HOR/HER), respectively. In‐depth mechanistic analysis demonstrates that an ideal dual‐sites cooperative mechanism achieves a suitable adsorption balance of Had and OHad, resulting in an energetically favorable Volmer step. This work offers new guidance for the precise construction of highly active SACs. [ABSTRACT FROM AUTHOR]

Lithium metal anodes are widely regarded as the ideal candidate for the next generation of high‐energy‐density lithium batteries. Here, a 3D host made of lithiophilic Mo2C clusters‐embedded carbon nanofibers (Mo2C@CNF) is developed. The uniformly dispersed clusters and large specific surface areas of Mo2C@CNF provide numerous nucleation sites for lithium deposition. Mo2C clusters exhibit ultralow nucleation overpotential compared to MoO2, which is also supported by density functional theory calculations. Furthermore, the transition metal element serves as a catalyst for the formation of a stable and robust solid electrolyte interphase layer containing LiF on Mo2C@CNF, effectively mitigating the occurrence of dead lithium and enhancing the Coulombic efficiency during prolonged operation. As a result, the Mo2C@CNF composite delivers superior electrochemical performance (>1600 h) at 1 mA cm−2 and lower nucleation overpotential (13 mV) for lithium plating. The Li/Mo2C@CNF anode coupled with the commercial LiFePO4 cathode exhibits excellent cycling stability (300 cycles at 1 C) and high rate capability at low N/P ratios. [ABSTRACT FROM AUTHOR]

The direct correlation between active sites and catalytic activity in multiple‐component metal‐organic frameworks (MOFs) is key to understanding their mechanism of oxygen evolution reaction (OER) but remains vague. Herein, supported multiple‐site MOFs are adopted as model catalysts to quantitatively study the composition‐dependent OER performance. Ni MOFs on Fe metal substrate possess the highest intrinsic OER activity with the Ni/Fe ratio of 1:2 in the presence of metal leaching of the substrate during synthesis. Further introducing a proper amount of Cu further boosts the OER performance of Cu‐doped NiFe MOFs with an impressively low overpotential of 200 mV at 10 mA cm−2. Spectroscopic analysis with theoretical study indicates that the copper doping within the NiFe MOFs induces electron redistribution for high valence Fe sites with an optimized balance of OH/OOH adsorption and decreased energy barrier for improved OER. This work sheds light on the active site tailoring of MOFs which highly correlates with the OER activity. [ABSTRACT FROM AUTHOR]

Ni was introduced to FeWO 4 self-supporting electrode via a spontaneous redox reaction to break the symmetry of the FeO 6 octahedron, which facilitated the reconstitution and promoted the OER intrinsic activity of Fe sites in tungstate, leading to ultralow overpotentials at high current densities and superior stability of 500 h. [Display omitted] Electronic structure manipulation with regard to active site coordination is an effective strategy to improve the electrocatalytic oxygen evolution reaction (OER) activity. Herein, we present the structure–activity relationship between oxygen-atom-mediated electron rearrangement and active site coordination asymmetry. Ni2+ ions are introduced to FeWO 4 on Ni foam (NF) via self-substitution to break the symmetry of the FeO 6 octahedron and regulate d -electron structure of Fe sites. Structural regulation optimizes the adsorption energy of hydroxyl on the Fe sites and promotes the partial formation of hydroxyl oxide with high OER activity on the tungstate surface. Fe 0.53 Ni 0.47 WO 4 /NF with the asymmetric FeO 6 octahedron of Fe sites can achieve an ultralow overpotential of 170 mV at 10 mA cm−2 and 240 mV at 1000 mA cm−2 with robust stability for 500 h at high current density under alkaline conditions. This research develops novel electrocatalysts with impressive OER performance and provides new insights into the design of highly active catalytic systems. [ABSTRACT FROM AUTHOR]

Coupling urea oxidation reaction (UOR) with hydrogen evolution reaction (HER) is an effective energy-saving technique for hydrogen generation. However, exploring efficient bifunctional electrocatalysts under high current density is still challenging. Herein, hierarchical Fe doped cobalt selenide coupled with FeCo layered double hydroxide (Fe-Co085Se/FeCo LDH) array as a self-supported superior bifunctional heterojunction electrode is rationally designed for both UOR and HER. The unique heterostructure facilitates electron transfer and interface interactions through local interfacial Co-Se/O-Fe bonding environment modulation, improving reaction kinetics and intrinsic activity. As a result, the heterostructured electrocatalyst exhibits ultralow potentials of -0.274 and 1.48 V to reach 500 mA cm-2 for catalyzing the HER and UOR, respectively. Particularly, the full urea electrolysis system driven by Fe-Co085Se/FeCo LDH delivers 300 mA cm-2 at a relatively low potential of 1.57 V, which is 150 mV lower than the conventional water electrolysis. The combination of in situ characterization and theoretical analysis reveal that the active sites with the adjustable electronic environment are induced by the interfacial bonding of the heterojunction, facilitating the water decomposition ofHER and the stabilization of intermediates in UOR. This work inspires the interfacial environment modulation to optimize advanced electrocatalysts for energy-saving H2 production. [ABSTRACT FROM AUTHOR]

Rational heterointerface engineering is crucial for superior and robust hydrogen evolution reaction (HER). Herein, a delicate organic‐inorganic hybrid heterojunction based on the assembly of oxalate with polyaniline (PANI) for HER at high‐current‐densities is envisioned. Strong π–d electron coupling is achieved between the delocalized π electrons of PANI and the localized d electrons of oxalate metal sites. The CoC2O4 nanosheets are grown on nickel foam (NF) with Ni2+ ions substitution by the precursor etching. By virtue of the synergy of hetero ions and π–d electron coupling, metal sites obtain sufficient exposure and electronic structure optimization. Surprisingly, the phase transition of oxalate during HER in the alkaline environment does not weaken the π–d electronic coupling of the organic‐inorganic hybrid interfaces. Inheritable interfacial electron interaction provides a reliable guarantee for robust stability at high‐current‐densities while endowing the hybrid materials with extremely low overpotentials. As expected, post‐phase reconstructed Co0.59Ni0.41(OH)2@PANI/NF displays impressive HER activity, with a low overpotential of 43 mV@−10 mA cm−2 and robust stability at −1000 mA cm−2 for 30 h in the alkaline environment. This study sheds light on the rational heterostructure interface design and promotes the architecture of an impressive electrocatalysts system. [ABSTRACT FROM AUTHOR]

Designing well‐defined interfacial chemical bond bridges is an effective strategy to optimize the catalytic activity of metal–organic frameworks (MOFs), but it remains challenging. Herein, a facile in situ growth strategy is reported for the synthesis of tightly connected 2D/2D heterostructures by coupling MXene with CoBDC nanosheets. The multifunctional MXene nanosheets with high conductivity and ideal hydrophilicity as bridging carriers can ensure structural stability and sufficient exposure to active sites. Moreover, the Co–O–Ti bond bridging formed at the interface effectively triggers the charge transfer and modulates the electronic structure of the Co‐active site, which enhances the reaction kinetics. As a result, the optimized CoBDC/MXene exhibits superior hydrogen evolution reaction (HER) activity with low overpotentials of 29, 41, and 76 mV at 10 mA cm−2 in alkaline, acidic, and neutral electrolytes, respectively, which is comparable to commercial Pt/C. Theoretical calculation demonstrates that the interfacial bridging‐induced electron redistribution optimizes the free energy of water dissociation and hydrogen adsorption, resulting in improved hydrogen evolution. This study not only provides a novel electrocatalyst for efficient HER at all pH conditions but also opens up a new avenue for designing highly active catalytic systems. [ABSTRACT FROM AUTHOR]

Herein, we present a facile plasma-induced strategy to introduce plentiful oxygen vacancies in porous metal–organic framework nanosheet arrays (Ov-Fe MOF/IF). The pore structure and coordinatively unsaturated metal sites endow the Ov-Fe MOF/IF with more active sites and accelerated reaction kinetics, thereby exhibiting a low potential of 1.51 V at 10 mA cm−2 for water splitting, which outperforms most MOF-based electrocatalysts. [ABSTRACT FROM AUTHOR]

Developing efficient bifunctional electrocatalysts toward oxygen/hydrogen evolution reactions is crucial for electrochemical water splitting toward hydrogen production. The high‐performance electrocatalysts depend on the catalytically active and highly accessible reaction sites and their structural robustness, while the rational design of such electrocatalysts with desired features avoiding tedious manufacture is still challenging. Here, a facile method is reported to synthesize mesoporous and heterostructured transition metal oxides strongly anchored on a nickel skeleton (MH‐TMO) containing identified Fe–Cu oxide interfaces with high intrinsic activity, easy accessibility for reaction intermediates, and long‐term stability for alkaline oxygen/hydrogen evolution reactions. The MH‐TMO with the electrocatalytically active Fe–O–Cu bridge has an optimal oxygen binding energy to facilitate adsorption/desorption of oxygen intermediates for oxygen molecules. Associated with the high mass transport through the nanoporous structure, MH‐TMO exhibits impressive oxygen evolution reaction catalysis, with an extremely low overpotential of around 0.22 V at 10 mA cm−2 and low Tafel slope (44.5 mV dec−1) in 1.0 M KOH, realizing a current density of 100 mA cm−2 with an overpotential as low as 0.26 V. As a result, the alkaline electrolyzer assembled by the bifunctional MH‐TMO catalysts operates with an outstanding overall water‐splitting output (1.49 V@10 mA cm−2), outperforming one assembled with noble‐metal‐based catalysts. [ABSTRACT FROM AUTHOR]

Engineering of structure and composition is essential but still challenging for electrocatalytic activity modulation. Herein, hybrid nanostructured arrays (HNA) with branched and aligned structures constructed by cobalt selenide (CoSe2) nanotube arrays vertically oriented on carbon cloth with CoNi layered double hydroxide (CoSe2@CoNi LDH HNA) are synthesized by a hydrothermal‐selenization‐hybridization strategy. The branched and hollow structure, as well as the heterointerface between CoSe2 and CoNi LDH guarantee structural stability and sufficient exposure of the surface active sites. More importantly, the strong interaction at the interface can effectively modulate the electronic structure of hybrids through the charge transfer and then improves the reaction kinetics. The resulting branched CoSe2@CoNi LDH HNA as trifunctional catalyst exhibits enhanced electrocatalytic performance toward oxygen evolution/reduction and hydrogen evolution reaction. Consequently, the branched CoSe2@CoNi LDH HNA exhibits low overpotential of 1.58 V at 10 mA cm−2 for water splitting and superior cycling stability (70 h) for rechargeable flexible Zn‐air battery. Theoretical calculations reveal that the construction of heterostructure can effectively lower the reaction barrier as well as improve electrical conductivity, consequently favoring the enhanced electrochemical performance. This work concerning engineering heterostructure and topography‐performance relationship can provide new guidance for the development of multifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

Dual‐sites single atom catalysts hold promise for efficiently regulating multiple reaction processes and explicitly explaining the underlying mechanisms. However, delicate atomic engineering for dual‐site single atom catalysts remains a huge challenge. Herein, atomically dispersed Fe‐Ni single atoms embedded in a nitrogen‐doped carbon matrix (FeNi SAs/NC) are successfully developed with extraordinary activity for electrocatalytic oxygen reduction and evolution reactions (ORR/OER). The atomic FeNi SAs/NC catalyst displays high onset potential (0.98 V) and half‐wave potential (0.84 V) for the ORR, as well as, low overpotential of (270 mV) at 10 mA cm−2 for the OER. The density functional theory calculations indicate that the Fe site as the active center can facilitate the four‐electron reaction process, while Ni sites regulate the electronic structure of Fe sites and further reduce the energy barrier of the rate‐determining step. In addition, the nitrogen‐doped carbon matrix prevents the metal atoms from aggregation and corrosion, leading to the improvement of catalyst durability. As a proof of concept, flexible quasi‐solid‐state zinc– and aluminum–air batteries assembled with the FeNi SAs/NC catalyst exhibit superior peak power densities and discharging specific capacities outperforming the commercial Pt/C. This work provides rational guidance for the synthesis of bifunctional electrocatalysts in next‐generation energy devices for flexible consumer electronics. [ABSTRACT FROM AUTHOR]

In high demand is developing trifunctional electrocatalysts to simultaneously drive hydrogen evolution reaction (HER) and oxygen evolution/reduction reaction (OER/ORR) for metal-air batteries and water splitting. Here we develop the carbon nanotubes (CNTs)-grafted FeC/MnO 2 nanocomposite catalyst by carbonizing FeMn metal-organic frameworks. The synergistic effect between FeC and MnO 2 dominantly contributes the ORR, OER, and HER. The transition metal-mediated growth of CNTs by an in-situ catalysis mechanism enables high electrical conductivity, abundant active sites, as well as efficient reaction pathways. The optimized chemical composite and unique hierarchical structure endow the FeC/MnO 2 with low overpotentials for multiply electrochemical reactions. Consequently, the composite catalyst successfully serves as the bifunctional electrode for water splitting with a voltage of 1.66 V at 10 mA cm−2 as well as the cathode for all-solid-state metal-air battery with Pt/C-comparable performance. The advanced transition metal composite presented in this work provides the guidance for rationally developing trifunctional electrocatalysts for efficient integrated energy conversion systems. FeC/MnO 2 , as an advanced trifunctional catalyst that can be used for water splitting and metal-air batteries, benefits from strong synergy, abundant active sites and efficient electron transfer rate. [Display omitted] • FeC/MnO 2 is electrocatalytically active and stable for OER, ORR and HER. • The porous structure provides abundant active sites and proton transfer channels. • The combination of CNTs and FeC/MnO 2 increases the electron transfer rate. • The internal synergy of FeC/MnO 2 plays a major role in electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Synthesis of highly efficient, non-noble and bi-functional electrocatalysts is exceedingly challenging and necessary for water splitting devices. In this work, three-dimensional spherical Ni(OH) 2 /NiCo 2 O 4 heterojunctions are prepared by a one-step hydrothermal method and the hybrids are explored as efficient electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte via tuning different Ni/Co atomic ratios of heterojunctions. The optimized Ni(OH) 2 /NiCo 2 O 4 (S (1:1)) exhibits high electrocatalytic activity with an ultralow over-potential of 189 mV at 10 mA cm−2 for the HER. With regard to the OER, the over-potential of the as-synthesized S (1:1) heterojunction is only 224 mV at the current density of 10 mA cm−2. The improved catalytic performance of the Ni(OH) 2 /NiCo 2 O 4 heterojunctions is attributed to the chemical synergic combining of Ni(OH) 2 and NiCo 2 O 4 , large specific surface area for exposing more accessible active sites, and heterointerface for activating the intermediates that facilitates electron/electrolyte transport. The prepared catalyst exhibits good durability and stability in HER and OER catalyzing conditions. This study provides a feasible approach for the building of highly efficient bifunctional water splitting electrocatalysts and stimulates the development of renewable energy conversion and storage devices. • The three-dimensional spherical Ni(OH) 2 /NiCo 2 O 4 heterojunctions were constructed. • The heterostructure would improve electrocatalytic performance. • The optimized catalyst exhibits remarkable catalytic activity for water splitting. • The S (1:1) heterojunction exhibits an overpotential of 224 mV for OER and 189 mV for HER. [ABSTRACT FROM AUTHOR]

Herein, novel and durable single-layer carbon-coated FeCo alloy nanoparticles embedded in single-walled carbon nanotubes (FeCo/SWCNTs) are rationally synthesized using a facile one-step route by aerosol-assisted floating catalyst chemical vapor deposition (CCVD). The as-synthesized unique FeCo/SWCNT catalyst exhibits remarkable oxygen electrocatalysis performance, especially oxygen evolution reaction activity and superior stability owing to the efficient synergistic effect between FeCo alloy and single-layer carbon regarding the electronic interaction and surface protection, achieving an overpotential (η) of 253 mV at 10 mA cm−2 and a Tafel slope of 44 mV dec−1 in 1.0 M KOH solution while presenting outstanding stability after being tested for 50 hours. Such high oxygen electrocatalysis performance advances realistic renewable zinc–air batteries with high efficiency as well. [ABSTRACT FROM AUTHOR]

Seeking a multifunctional electrocatalyst composed of earth-abundant elements for highly hydrogen and oxygen evolution reaction and oxygen reduction reaction (HER, OER and ORR) is technically imperative for the electrocatalytic applications. Herein, we report HER, OER and ORR electrocatalytic performances of metal-organic framework (MOF) derived cobalt nanoparticles encapsulated in nitrogen-doped carbon and carbon nanotube (Co@NC/CNT). The optimized Co@NC/CNT hybrid shows superior HER and OER activities with a small overpotential of 137 mV and 302 mV at a current density of 10 mA cm−2, respectively. Furthermore, the Co@NC/CNT as an air-cathode in secondary Zn-air battery demonstrates a confined potential gap of 0.88 V over 200 h and a maximum power density of 53.4 mW cm−2, which are much better than those of Pt/C. The outstanding performances are attributed to the synergistic effects from Co, and N embedded into carbon and CNT. More importantly, the unique surface structure contributes to expose many active sites for superior catalytic activity through allowing a large number of electrons. These outcomes not only prove a facile approach for the preparation of metals/carbon hybrid but also disclose its huge possible as a multifunctional electrocatalyst for sustainable energy systems. • Co@NC/CNT derived from metal-organic framework (MOF) is designed and prepared. • Co@NC/CNT as a tri-functional electrocatalyst exhibits superior HER, OER and ORR activity. • The outstanding performance is attributed to the synergistic offerings from Co, and N embedded into carbon and CNT. • The result provides huge possible as a multi-functional electrocatalyst for sustainable energy systems. [ABSTRACT FROM AUTHOR]

Developing of inexpensive, high-efficient, and earth-abundant bifunctional catalysts for water splitting is of great significance for green and sustainable energy development. Herein, a bifunctional hybrid electrocatalyst of Ni 3 ZnC 0.7 nanodots in-situ grown on nitrogen-doped carbon nanotube (Ni 3 ZnC 0.7 /NCNT) arrays is synthesized by a one-step template strategy with 1, 3, 5-triamino-2, 4, 6-trinitrobenzene serving as carbon/nitrogen sources, ZnO nanorods as template and zinc source, and nickel foam as substrate and nickel source. Benefiting from the introduction of Ni 3 ZnC 0.7 nanodots and nitrogen doping to the carbon nanotubes, the Ni 3 ZnC 0.7 /NCNT-700 arrays exhibit superior hydrogen evolution reaction and oxygen evolution reaction catalytic activity in terms of low overpotential (203 mV and 380 mV vs RHE at 10 mA cm−2 for hydrogen evolution reaction and oxygen evolution reaction, respectively). When the Ni 3 ZnC 0.7 /NCNT-700 is served as both anode and cathode catalysts for overall water splitting, a potential of 1.66 V is needed to deliver a current density of 10 mA cm−2, and it also displays negligible degradation after 24 h of operation in alkaline solution. The present work not only provides an efficient bifunctional electrocatalyst for overall water splitting, but also offers a new strategy to design and synthetize the bimetallic carbide. Image 1 [ABSTRACT FROM AUTHOR]

Designing a highly efficient electrocatalyst with more active sites and faster charge transfer is crucial to improve oxygen evolution reaction (OER) performance. Herein, hierarchically trimetallic Co 0.7 Fe 0.24 Ni 0.06 -BDC (1,4-benzenedicarboxylate, denoted as BDC) coordination polymers have been prepared via ion-exchange by immersing Co-BDC micro-flowers into bimetallic solution under mild conditions. This strategy introduces the other transition metal ions into Co-BDC micro-flower structure without destroying Co-BDC superior flower-like morphology. As electrocatalyst in OER, Co 0.7 Fe 0.24 Ni 0.06 -BDC exhibits an outstanding performance with a small overpotential of 291 mV at 50 mA·cm−2 and a Tafel slope of 60.8 mV·dec−1. Durability of Co 0.7 Fe 0.24 Ni 0.06 -BDC is demonstrated by long-term electrochemical stability for 12 h at current density of 10 mA·cm−2. This enhanced OER activity of Co 0.7 Fe 0.24 Ni 0.06 -BDC micro-flowers attribute to the superior morphology of micro-flowers and the synergistic effect of tri-metal, inducing the presence of abundant active sites and fast charge transfer. This work suggests that Co 0.7 Fe 0.24 Ni 0.06 -BDC micro-flowers have great practical potential in the field of OER. • Trimetallic Co 0.7 Fe 0.24 Ni 0.06 -BDC micro-flowers was synthesized in room temperature. • Flower-like structure provides abundant active sites, which is crucial to improve OER activity. • Synergistic effect of tri-metal boosts the OER activity. • Co 0.7 Fe 0.24 Ni 0.06 -BDC/NF exhibit excellent OER activity and great long-term stability. [ABSTRACT FROM AUTHOR]

Benefiting from the structure and electronic engineering, the self-supported N doped NiSe 2 hierarchically nanoflake arrays grown on flexible carbon cloth present superior performance with high stability and robust flexibility for solid-state zinc-air batteries. • The self-supported cathode electrode can satisfy the flexibility for solid-state zinc-air batteries. • Nitrogen doping can optimize the electronic structure and absorption feature of NiSe 2. • The open and porous structure provides more active sites and facilitates the mass transfer process. • N-NiSe 2 /CC exhibits outstanding performance for oxygen evolution/reduction reaction and zinc-air batteries. Rational design of efficient bifunctional air cathodes towards oxygen evolution/reduction reaction is of central importance for energy-efficient metal-air batteries, but remains an ongoing challenge. Here, N element doped NiSe 2 nanosheets in-situ grown on the carbon cloth were prepared via facial hydrothermal synthesis of nickel hydroxide followed by selenization and nitrogen doping treatment. Such self-supported N-doped NiSe 2 nanoarrays (N-NiSe 2 /CC) exhibits superior bifunctional catalytic activity and high durability compared with the pristine NiSe 2 /CC, which are ascribed to the unique structure after nitrogen doping. Nitrogen doping can provide more electrocatalytical active sites and improve the electronic transport for fast reaction kinetics, which is preferably corroborated with density functional theory calculations and X-ray absorption spectroscopy. As a proof of concept, the solid-state zinc-air batteries assembled by the N-NiSe 2 /CC directly as the air cathode present a low overpotential of 0.75 V, remarkable cyclic stability of 30 h with 90 circles, and robust flexibility. Therefore, the N-NiSe 2 /CC system proves to be a highly active and reliable electrode for the developing of metal-air batteries, opening up a promising opportunity for high-performance portable electronics. [ABSTRACT FROM AUTHOR]