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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]

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]

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]

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]

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]