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Water electrolysis is a promising method for producing ultra‐pure hydrogen as a sustainable energy source in the future. In this study, the use of a hollow‐structured Fe‐doped CoP with an abundance of phosphorus defects for both oxygen and hydrogen evolution reactions (OER and HER) is suggested. The as‐prepared electrocatalyst has a low overpotential of 300 and 143 mV to achieve a current density of 10 mA cm−2 for the OER and HER, respectively. When the synthesized electrocatalyst is used as both anode and cathode in a water electrolyzer, the full cell requires a very small cell voltage of 1.63 V at 10 mA cm−2 and exhibits excellent stability for over 100 h. The excellent performance is due to the generation of numerous electrocatalytic active sites induced by introduction of structural defects such as Fe dopants and P vacancies, which modify the adsorption energy of reaction intermediates during water electrolysis. This study can offer new insights into the development of efficient precious metal‐free electrocatalysts for production of renewable energy sources. [ABSTRACT FROM AUTHOR]

Herein, mesoporous NiFe2O4 spinel nanoparticles with abundant oxygen vacancies are successfully prepared by a simple hydrothermal method followed by mild H2 reduction and used as catalysts for the oxygen evolution reaction. Compared with the pristine and air‐treated NiFe2O4, the H2‐treated NiFe2O4 shows a much lower overpotential of 389 mV at a current density of 10 mA cm−2. The H2‐treated NiFe2O4 also indicates substantial long‐term stability even after 1000 cyclic tests. This outstanding electrochemical activity and stability can be attributed to the improved physicochemical properties by H2 treatment: small nanoparticles with well‐developed mesoporous structures, a high ratio of Ni2+/Ni3+ cations, and abundant oxygen vacancies. These properties can significantly improve charge transfer kinetics and increase the number of active sites on the catalyst. The results demonstrate that this facile fabrication method is a promising route for developing cost‐effective and high‐performance catalysts to be used in electrochemical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploring precious metal-free bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is essential for the practical application of rechargeable Zn-air battery (ZAB). Herein, Ni-doped Co 9 S 8 nanoparticles embedded in a defect-rich N, S co-doped carbon matrix (d-Ni x Co 9-x S 8 @NSC) are synthesized via a facile pyrolysis and acid treatment process. The introduction of abundant defects in both the carbon matrix and metal sulfide provides numerous active sites and significantly enhances the electrocatalytic performances for both the ORR and OER. d-Ni x Co 9-x S 8 @NSC exhibits a superior half-wave potential of 0.841 V vs. RHE for the ORR and delivers a low overpotential of 0.329 V at 10 mA cm−2 for the OER. Additionally, Zn-air secondary battery using d-Ni x Co 9-x S 8 @NSC as the air cathode displays a higher specific capacity of 734 mAh g Zn −1 and a peak power density of 148.03 mW cm−2 compared to those of state-of-the-art Pt/C-RuO 2 (673 mAh g Zn −1 and 136.9 mW cm−2, respectively). These findings underscore the potential of d-Ni x Co 9-x S 8 @NSC as a high-performance electrocatalyst for secondary ZABs, offering new perspectives on the design of efficient noble metal-free electrocatalysts for future energy storage and conversion applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe and F dual-doped CoS 2 are prepared by anion exchange and heat treatment process. • Dual doping strategy increases reaction kinetics and intrinsic catalytic activity. • Uniform hollow structure enhances the number of exposed active sites for OER. • DFT calculation reveal that the dual-dopants modifies energy states during the OER. Utilizing renewable electricity for water electrolysis offers a promising way for generating high-purity hydrogen gases while mitigating the emission of environmental pollutants. To realize the water electrolysis, it is necessary to develop highly active and precious metal-free electrocatalyst for oxygen evolution reaction (OER) which incurs significant overpotential due to its complicated four-electron transfer mechanism. Hence, we propose a facile preparation method for hollow-structured Fe and F dual-doped CoS 2 nanosphere (Fe-CoS 2 -F) as an efficient OER electrocatalyst. The uniform hollow and porous structure of Fe-CoS 2 -F enlarge the specific surface area and increase the number of exposed active sites. Furthermore, the Fe and F dual-dopants synergistically contributed to the adjustment of electronic structure, thereby promoting the adsorption/desorption of oxygen-containing reaction intermediates on active sites during the alkaline OER procedure. As a result, the prepared Fe-CoS 2 -F exhibits outstanding OER activity, characterized by a low overpotential of 298 mV to achieve a current density of 10 mA cm−2 and a Tafel slope as small as 46.0 mV dec−1. Based on computational theoretical calculations, the introduction of the dual-dopants into CoS 2 structure reduce the excessively strong adsorption energy of reaction intermediate in the rate determining step, leading to effectively promoted electrocatalytic cycle for OER in alkaline environment. This study presents an effective strategy for preparing noble metal-free OER electrocatalysts with promising potential for large-scale industrial water electrolysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co and N dual-doped Ni 2 P grown on nickel foam was prepared by hydrothermal and annealing process. • Partial electron transport into host material induced by cobalt dopants effectively generate electron-rich active sites. • Nitrogen dopants make the metal species have high valence states and increase the surface polarity of electrocatalyst. • The Co-Ni 2 P-N/NF showed excellent electrocatalytic activity and stability for both OER and UOR. The development of efficient bifunctional electrocatalysts for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is critical for hydrogen production and wastewater purification. In this work, we propose a facile synthetic method for Co and N dual-doped Ni 2 P directly grown on Ni foam (Co-Ni 2 P-N/NF) using hydrothermal and annealing process. Simultaneous Co and N dual-doping into Ni 2 P not only modifies the surface electronic structure, but also generates a multitude of active sites with high valence states, which are beneficial for improving electrocatalytic kinetics for both OER and UOR. As a result, the Co-Ni 2 P-N/NF catalyst exhibits a low overpotential of 329 mV to deliver a current density of 100 mA cm−2 for OER in alkaline solution, which is much lower than that of the state-of-the-art RuO 2 electrocatalyst. In addition, the urea-assisted water oxidation process exhibits a significant reduction of approximately 163 mV in the required potential at 100 mA cm−2 compared to that of the OER, which highlights the remarkable potential of the prepared Co-Ni 2 P-N/NF electrocatalyst in facilitating the purification of wastewater and hydrogen production with significantly lower energy consumption. [ABSTRACT FROM AUTHOR]

Herein, strongly coupled Ni 3 S 2 /MoS 2 hollow spheres derived from NiMo-based bimetal-organic frameworks are successfully synthesized for overall water splitting via a one-pot solvothermal method followed by sulfurization. A well-defined hollow spherical structure with a heterointerface between Ni 3 S 2 and MoS 2 is constructed using solvothermal and sulfurization processes. Owing to their bimetallic heterostructure, porous hollow carbon structure with large surface area, and numerous exposed active sites, the Ni 3 S 2 /MoS 2 hollow spheres are found to be efficient electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The heterostructured Ni 3 S 2 /MoS 2 hollow spheres show small overpotentials of 303 and 166 mV to reach a current density of 10 mA cm−2 for the OER and HER in 1.0 M KOH, respectively. Furthermore, an overall water-splitting electrolyzer consisting of the Ni 3 S 2 /MoS 2 hollow spheres as both the anode and cathode requires a very low cell voltage of 1.62 V to drive a current density of 10 mA cm−2 with outstanding long-term stability for 100 h. Our findings offer a new pathway for the design and synthesis of electrochemically advanced bifunctional catalysts for various energy storage and conversion applications. [Display omitted] • Ni 3 S 2 /MoS 2 was synthesized using a one-pot solvothermal method followed by sulfurization. • The synergistic effect of binary metal and unique structure led to excellent OER and HER activity. • Ni 3 S 2 /MoS 2 hollow spheres indicated outstanding catalytic activities and stability. [ABSTRACT FROM AUTHOR]

Herein, a strongly coupled Cu 3 P/FeP heterostructure with P-doped carbon derived from MIL-101 was synthesized via a three-step method involving solvothermal, carbonization, and phosphidation processes. The Cu 3 P/FeP heterostructure serves as a good catalyst because it possesses abundant interfaces between Cu 3 P and FeP, which enables the exposure of electrocatalytically active sites and tuning of surface electronic configurations. Additionally, the presence of strong heterointerfaces between Cu 3 P and FeP, and the integration of the P-doped carbon guarantee the high electrical conductivity of the catalyst. Benefiting from these advantages, the Cu 3 P/FeP electrode exhibited outstanding electrocatalytic activity toward the oxygen evolution reaction (OER), which presents a low overpotential of 315 mV to drive a current density of 10 mA cm−2 in 1.0 M KOH, thus outperforming that of the state-of-the-art RuO 2. In addition, the Cu 3 P/FeP hybrid composite exhibited long-term stability for 50 h. This work provides a new strategy for the design and preparation of transition-metal-based heterostructures and facilitates the development of high-performance energy-related materials. [Display omitted] • Cu 3 P/FeP on P-doped carbon was synthesized through a solvothermal process followed by a phosphidation treatment. • Abundant heterointerfaces led to a notable enhancement of catalytic activity toward the OER. • Cu 3 P/FeP exhibited a low overpotential of 315 mV at 10 mA cm−2 and long-term durability over 50 h. [ABSTRACT FROM AUTHOR]

Transition metal-based heterostructure materials are considered as promising alternatives to state-of-the-art noble metal-based catalysts toward the oxygen evolution reaction (OER). Herein, for the first time, a simple interface engineering strategy is presented to synthesize efficient electrocatalysts based on a novel CoFe 2 O 4 /β-Ni(OH) 2 heterogeneous structure for the electrochemical OER. Remarkably, the optimized CoFe 2 O 4 /β-Ni(OH) 2 electrocatalyst, benefiting from its hierarchical hexagonal heterostructure with strong electronic interaction, enhanced intrinsic activity, and electrochemically active sites, exhibits outstanding OER electrocatalytic performance with a low overpotential of 278 mV to reach a current density of 10 mA cm−2, a small Tafel slope of 67 mV dec−1, and long-standing durability for 30 h. Its exceptional OER performance makes the CoFe 2 O 4 /β-Ni(OH) 2 heterostructure a prospective candidate for water oxidation in alkaline solution. The proposed interface engineering provides new insights into the fabrication of high-performance electrocatalysts for energy-related applications. [Display omitted] • CoFe 2 O 4 /β-Ni(OH) 2 was synthesized by a simple interface engineering strategy. • The unique architecture with heterointerface led to outstanding OER performance. • CoFe 2 O 4 /β-Ni(OH) 2 indicated a low overpotential and long-term durability. [ABSTRACT FROM AUTHOR]

• Bimetallic Fe 0.64 Ni 0.36 Alloys were prepared by a hydrothermal method followed by mild H 2 reduction. • The binary metal alloys exhibited a low overpotential and substantial long-term stability for oxygen evolution reaction. • This outstanding OER performance and durability can be attributed to the synergistic effect of binary metal. In this study, binary NiFe alloy nanoparticles are successfully prepared using a simple hydrothermal method followed by H 2 reduction. The nanoparticles are then applied as electrocatalysts for oxygen evolution reaction (OER). Compared to unary Ni or Fe, the binary NiFe alloy electrocatalyst exhibits a much lower overpotential of 298 mV at a current density of 10 mA cm−2, and it exhibits electrocatalytic activity for OER superior to that of state-of-the-art RuO 2 and IrO 2 noble metal oxide catalysts. Moreover, the alloy catalyst exhibits substantial long-term durability after 1000 cyclic voltammetry tests. This remarkable electrochemical performance mainly originates from the synergistic effects of Fe incorporation into Ni species, leading to the improved charge transfer kinetics and intrinsic activity of the catalyst. These results provide a promising avenue for developing cost-effective and high-performance electrocatalysts as advanced electrodes for energy storage and conversion systems. [ABSTRACT FROM AUTHOR]

Water electrolysis has been regarded as ideal method for producing high-purity hydrogen without the generation of environmental pollutants. Accordingly, the development of precious metal-free electrocatalysts that demonstrate high activity for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is essential for practical water electrolysis. Herein, porosity-engineered Ti 3 C 2 MXene is employed as an efficient substrate for a bimetallic Ni-Fe-S electrocatalyst. The porous and defect-rich Ti 3 C 2 (D -Ti 3 C 2) flakes provide metal-like electrical conductivity and large surface area for direct growth of active species. Simultaneously, the Ni-Fe-S nanoparticles, constructed through a strong coupling between NiS 2 and (Ni,Fe)S 2 solid solution, not only serve as active sites with rich redox properties, but also generate charge transfer channels for electrochemical reactions. Leveraging these advantageous properties, the resulting Ni-Fe-S/ D -Ti 3 C 2 electrocatalyst exhibits excellent bifunctional electrocatalytic performance toward both OER and HER. As a result, the symmetric water electrolysis cell using the Ni-Fe-S/ D -Ti 3 C 2 requires a low cell voltage of 1.621 V to deliver current density of 10 mA cm−2, and shows stable electrocatalytic performance over 100 h of continuous operation. [Display omitted] • Bimetallic Ni-Fe-S grown on defect-rich Ti 3 C 2 MXene was prepared by facile wet-chemistry method. • The porous Ti 3 C 2 flakes provide metal-like electrical conductivity and large surface area for growth of active species. • Bimetallic Ni-Fe-S provides rich redox properties and efficient charge transfer channel for electrochemical reactions. • The prepared electrocatalyst showed excellent electrocatalytic activity and stability for overall water electrolysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Heterostructured Co 4 N/CeO 2 nanoparticles are prepared using bimetallic BTC MOF. • The rough surface and mesoporous structure enhance exposure of active sites. • Abundant heterointerfaces and oxygen vacancies offer effective active sites for OER. • Co 4 N/CeO 2 -2.7 exhibited low overpotential and Tafel slope with superior durability. In this study, Co– and Ce-based bimetal organic frameworks are employed as self-templates for the synthesis of CeO 2 -decorated Co 4 N (Co 4 N/CeO 2) nanoparticles with strongly coupled heterointerfaces. The rough surface and well-developed mesoporous structure of Co 4 N/CeO 2 can enhance the exposure of electrochemically active sites. In addition, the lattice mismatch at the heterointerface between Co 4 N and CeO 2 introduces abundant oxygen vacancies, which moderately controls the electronic structure and provides efficient active sites for an alkaline OER. Consequently, the as-prepared Co 4 N/CeO 2 electrocatalyst exhibits superior OER activity: a small overpotential of 297 mV to acquire a current density of 10 mA cm−2, low Tafel slope of 81 mV dec−1, and a turnover frequency of 4.75 s−1 at an overpotential of 420 mV. Additionally, the Co 4 N/CeO 2 nanoparticles show an excellent long-term durability of more than 80 h of continuous electrocatalytic operation in an alkaline solution. [ABSTRACT FROM AUTHOR]

The development of efficient noble metal-free electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for practical applications in electrochemical water splitting. In this study, core@shell structured nickel cobalt alloy-nickel cobalt phosphide (NiCo@NiCoP) nanorods directly grown on nickel foam (NF) are successfully synthesized throughout hydrothermal, thermal reduction, anodic oxidation, and phosphidation process. The NiCoP shell contributes to excellent redox performance in the electrochemical reaction, while the NiCo alloy core functions as an electron highway, enhancing the electrical conductivity and charge transfer efficiency. The synthesized NiCo@NiCoP/NF exhibits outstanding HER activity with a low overpotentials of 130 mV at a current density of − 100 mA cm−2 and a small Tafel slope of 36 mV dec−1. Additionally, the overpotential required to acquire a current density of 100 mA cm−2 and the Tafel slope is found to be 340 mV and 79 mV dec−1, respectively, for OER. Furthermore, a symmetric water electrolyzer using NiCo@NiCoP/NF as a bifunctional electrocatalyst requires a cell voltage of only 1.55 V to deliver a current density of 10 mA cm−2 and displays remarkable electrochemical durability of over 100 h. The facile synthetic procedure and excellent bifunctional electrocatalytic performance for both HER and OER would provide the great potential for practical application of water electrolysis and future energy conversion and storage technologies. [Display omitted] • Core@shell structured NiCo@NiCoP nanorods are directly grown on nickel foam. • NiCo alloy core and NiCoP shell act as electron highway and catalytic active site. • The prepared NiCo@NiCoP/NF exhibited low overpotentials for both HER and OER. • Alkaline water electrolyzer exhibited a low cell voltage of 1.55 V at a 10 mA cm–2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen vacancy-rich CoFe/CoFe 2 O 4 on hollow N-doped carbon sphere is prepared. • Formation of Mott–Schottky heterojunction improve the electrical conductivity. • Introduction of oxygen vacancies facilitate reaction kinetics for both ORR and OER. • Rechargeable Zn-Air battery with V o -CoFe/CoFe 2 O 4 @NC show high power density and durability. Exploring transition metal-based bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for implementing rechargeable Zn–air batteries (ZABs). Herein, we synthesized oxygen-vacancy-rich CoFe/CoFe 2 O 4 embedded in N-doped hollow carbon spheres (V o -CoFe/CoFe 2 O 4 @NC) through pyrolysis, carbonization, and partial reduction. The synergistic effect of introducing oxygen vacancies into CoFe 2 O 4 and the well-defined heterointerfaces between the CoFe alloy and spinel-type CoFe 2 O 4 moderately controlled the electronic structure and provided abundant active sites for the ORR and OER. V o -CoFe/CoFe 2 O 4 @NC exhibited high ORR activity (half-wave potential: 0.858 V and Tafel slope: 56 mV dec–1) and delivered a low overpotential (360 mV at 10 mA cm−2) for the OER. Moreover, rechargeable ZABs using V o -CoFe/CoFe 2 O 4 @NC as the air cathode revealed excellent open-circuit voltage (1.53 V), good power density (139.5 mW cm−2), and longer cycling durability than the state-of-the-art Pt/C-RuO 2. [ABSTRACT FROM AUTHOR]

The development of highly active non-precious metal-based electrocatalysts to accelerate the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an essential issue for practical application of metal–air batteries. Herein, hydrothermal and annealing processes are employed to prepare FeCo alloy nanoparticles in N-doped carbon shells on a defect-rich carbon support (FeCoNC/D). The introduction of defect-rich carbon support combined with the strong coupling of distributed FeCo alloy and N-doped carbon shell efficiently enhances the electrocatalytic activity. The FeCoNC/D exhibits superior bifunctional electrocatalytic activity with a half-wave potential of 892 mV (vs. RHE) for the ORR and an overpotential of 362 mV to drive a current density of 10 mA cm–2 for the OER. Moreover, Zn–air secondary battery prepared with FeCoNC/D displays a higher specific capacity of 725 mA h g Zn –1, a power density of 157 mW cm–2 at 245 mA cm–2, and long-term cycling stability compared to state-of-the-art Pt/C-RuO 2. [Display omitted] • FeCoNC supported on defective ketjenblack (FeCoNC/D) catalysts are synthesized. • Defective carbon offers high electrical conductivity and abundant active sites. • The synergy effect of FeCo alloy and N-doped carbon improves ORR and OER activity. • Rechargeable Zn-air battery with FeCoNC/D shows high power density and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co/CoTe was prepared via precipitation, reflux-hydrothermal, and hydrogen treatment. • The unique 3D structure promotes the exposure of active sites and ions diffusion. • Well-defined heterointerfaces improve the kinetics of OER and electrical conductivity. In this study, a three-step process involving precipitation, reflux-hydrothermal method, and hydrogen treatment leads to the formation of a Prussian blue analog (PBA)-derived Co/CoTe heterostructure featuring a unique hierarchical 3D structure. This framework facilitates efficient exposure of the catalytically active sites and fast diffusion of the electrolyte. Additionally, the well-defined metal/semiconductor heterointerfaces result in an overall electrical conductivity enhancement and promote the oxygen evolution reaction (OER) kinetics by lowering the activation energy. Owing to the synergistic effect of Co and CoTe, the Co/CoTe heterostructure displays high electrocatalytic activity for OER, attaining an overpotential of 400 mV to deliver a current density of 50 mA cm−2 and a low Tafel slope of 94.1 mV dec−1, which is superior to pure CoTe and Co counterparts. Furthermore, the Co/CoTe exhibits outstanding durability over 50 h without obvious change in alkaline media. The synthetic strategy reported in this paper provides new insights into the design and preparation of high-performance heterostructured materials of interest in energy-related applications. [ABSTRACT FROM AUTHOR]

[Display omitted] 3D polyhedral Fe-doped Co 3 O 4 nanoparticles derived from FeCo-based ZIF-67 are synthesized using a facile co-precipitation method followed by two-step heat treatment and exhibit excellent OER performance with a comparably low overpotential and outstanding long-term stability in alkaline media. • Defect-rich Fe-doped Co 3 O 4 nanoparticles were synthesized using bimetallic-organic framework. • The synergistic effect of Fe doping and oxygen vacancy led to excellent OER activity. • Defect-rich Fe-doped Co 3 O 4 indicated low overpotential and outstanding durability. Herein, oxygen-deficient Fe-doped Co 3 O 4 polyhedral nanoparticles derived from FeCo‐based bimetal–organic frameworks are prepared for the electrocatalytic oxygen evolution reaction (OER) via a facile self‐templating strategy. A well-defined rhombic dodecahedral structure with abundant oxygen vacancies was constructed based on the coprecipitation, carbonization, oxidation, and partial reduction process. The proposed synthetic method is effective for fabricating a bimetallic hierarchical structure with a rough surface and a moderately controlled electronic structure, which significantly facilitates charge and mass transfer and appropriately exposes the active sites for efficient electrocatalysis. Subsequently, the as-obtained defect-rich Fe-doped Co 3 O 4 nanoparticles was found to be a superior OER electrocatalyst, with a small overpotential of 318 mV required for a current density of 10 mA cm−2, a low Tafel slope of 76.8 mV dec−1, a turnover frequency of 0.1553 s−1 at an overpotential of 370 mV, and outstanding long-term durability in 1.0 M KOH. The proposed strategy will offer a new approach in the design and development of electrochemically active non-noble materials as advanced catalysts for various energy storage and conversion applications. [ABSTRACT FROM AUTHOR]

l P-NiCo 2 S 4 nanoneedles vertically grown on NF were synthesized using one-step phosphosulfurization strategy assisted with P 2 S 5. l The homogeneous 1D structure and the introduction of P dopant on NiCo 2 S 4 led to enhanced electrocatalytic OER performance. l P-NiCo 2 S 4 /NF indicated a low overpotential of 300 mV to acquire a current density of 50 mA cm−2 and long-term durability over 100 h. In this work, one-step phosphosulfurization is demonstrated to prepare P-doped nickel cobalt sulfide nanoneedles vertically decorated on nickel foam (P-NiCo 2 S 4 /NF) as an extremely efficient electrocatalyst toward the oxygen evolution reaction (OER). The phosphosulfurization is conducted on nickel cobalt carbonate hydroxide in the presence of P 2 S 5. The P-NiCo 2 S 4 nanoneedles on the nickel foam generate a synergistic effect that provides effective mass and electron transfer pathways, endows the electrocatalyst with a moderate electronic structure, and facilitates gas diffusion to enhance the electrocatalytic performance. The catalysts yield a small overpotential of 300 mV to reach a current density of 50 mA cm−2, Tafel slope as low as 70 mV dec−1, and long-term stability over 100 h. These findings highlight the practical feasibility of P-doped NiCo 2 S 4 on NF for water splitting and offer a new approach for efficiently preparing advanced electrocatalysts in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

Although phosphosulfide and P-doped sulfide materials have been widely reported as highly efficient electrocatalysts for the oxygen evolution reaction (OER), the practical application of these materials is severely hindered by their complicated fabrication method. This paper reports a facile preparation of 3D hierarchical flower-like P-doped Ni–Fe disulfide microspheres by successive hydrothermal and one-step phosphosulfidation, using P 2 S 5 as a source of phosphorus (P) and sulfur (S). Owing to the synergistic effect of the binary metal system, the introduction of P, and unique 3D porous architecture, the flower-like P-doped Ni–Fe disulfide microspheres deliver outstanding OER performance—an overpotential of 264 mV to achieve a current density of 10 mA cm−2, a significantly low Tafel slope of 48 mV dec−1, and excellent long-term durability over 50 h with negligible degradation in alkaline media. The fabrication method applied in this study can provide a new facile approach to the design and synthesis of P-doped metal sulfide materials for various electrochemical applications. Image 1 • P-doped Ni–Fe disulfide was synthesized using one-step phosphosulfidation. • The synergistic effect of binary metal and P doping led to excellent OER activity. • P-doped Ni–Fe disulfide indicated low overpotential and Tafel slope. [ABSTRACT FROM AUTHOR]

• Fe-doped Ni 3 S 2 nanoneedles supported on nickel foam are successfully synthesized. • This catalyst provides a current density of 10 mA cm−2 at a cell voltage of 1.58 V. • This catalyst displays excellent long-term stability even after 50 h. Fe-doped Ni 3 S 2 nanoneedles supported on nickel foam (NF) are reported as coupled oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrocatalysts for effective overall water splitting. The optimized Fe doping density, vertically grown nanoneedle structure without any binder on the conductive substrate, and abundant surface-active sites make the Fe-doped Ni 3 S 2 an efficient catalyst for both electrochemical reactions. The as-synthesized Fe-doped Ni 3 S 2 nanoneedles on NF show an outstanding electrocatalytic performance, only requiring an overpotential of 269 and 314 mV to provide 100 and −100 mA cm−2 for OER and HER, respectively. A water electrolyzer, assembled with the Fe-doped Ni 3 S 2 as both the anode and cathode, displays an exceptionally low onset potential of 1.39 V and achieves a current density of 10 mA cm−2 at a very low cell voltage of 1.58 V with excellent long-term stability for 50 h. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Water splitting system by transition metal-based catalysts has drawn much attention in renewable energy storage and conversion system. In this study, β-Ni(OH) 2 nanoplates with abundant oxygen vacancies were synthesized via the hydrothermal method followed by a partial reduction reaction in a mild hydrogen atmosphere, and applied to the oxygen evolution reaction (OER) in an alkaline solution. The β-Ni(OH) 2 nanoplates prepared by partial reduction in a hydrogen atmosphere at 100 °C exhibited a current density of 10 mA cm−2 at a low overpotential of 340 mV in 1 M KOH; the overpotential was much lower than those required for pristine β-Ni(OH) 2 nanoplates (391 mV) and air-treated β-Ni(OH) 2 nanoplates (369 mV). Furthermore, the H 2 -treated β-Ni(OH) 2 nanoplates also displayed outstanding long-term stability even after 1000 cyclic voltammetry cycles. This excellent OER activity and stability could be ascribed to the abundant oxygen vacancies and a well-defined hexagonal structure. It is worth noting that this method will offer a facile synthesis of metal hydroxides for generating oxygen vacancy, improving the electrochemical performance of energy storage applications. Image 1 [ABSTRACT FROM AUTHOR]