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Designing an excellent OER catalyst in an alkaline environment is severe yet essential for industrial H2 application under the electrochemical technique. This study has achieved multiple modifications on CoN nanowires, the classic OER catalyst, via a facile room-temperature NaBH4 spontaneous hydrolysis. This facile process simultaneously generates oxygen vacancies and robust BN species. It wraps hydrophilic BOx motifs on the OER response CoN nanowires, producing OER active Co–N–B species, increasing active numbers and guaranteeing structural stability. It suggests that a low NaBH4 concentration (0.1 mol L−1) treatment endows CoNNWAs/CC with excellent OER performance and robust structure, which can drive a current density of 50 mA cm−2 with only 325 mV overpotentials with more than 24 hours' durability. Even, the catalyst can drive 1000 mA cm−2 around 480 mV overpotential. This study allows a novel strategy for designing high-performance OER catalysts. [ABSTRACT FROM AUTHOR]

The conventional electrolytic water‐splitting process for hydrogen production is plagued by high energy consumption, low efficiency, and the requirement of expensive catalysts. Therefore, finding effective, affordable, and stable catalysts to drive this reaction is urgently needed. We report a nanosheet catalyst composed of carbon nanotubes encapsulated with MoC/Mo2C, the Ni@MoC‐700 nanosheet showcases low overpotentials of 275 mV for the oxygen evolution reaction and 173 mV for the hydrogen evolution reaction at a current density of 10 mA ⋅ cm−2. Particularly noteworthy is its outstanding performance in a two‐electrode system, where a cell potential of merely 1.64 V is sufficient to achieve the desired current density of 10 mA ⋅ cm−2. Furthermore, the catalyst demonstrates exceptional durability, maintaining its activity over a continuous operation of 40 hours with only minimal attenuation in overpotential. These outstanding activity levels and long‐term stability unequivocally highlight the promising potential of the Ni@MoC‐700 catalyst for large‐scale water‐splitting applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Heterojunction can effectively improve oxygen evolution reaction (OER) activity by regulating the interfacial electronic structure of catalysts. However, p-p type heterojunction OER catalysts have obtained less attention, and the corresponding catalytic mechanisms are unclear either. Herein, the self-supported CoP-CoO p-p type heterojunction arrays are fabricated on carbon cloth substrate (CoP-CoO/CC). Band structure analysis shows that the formation of p-p heterojunction can drive the electrons from CoO to flow into CoP. This electronic modulation contributes to positively charged regions on the CoO and enhances the OH− adsorption during OER, proven by X-ray photoelectron spectroscopy and methanol molecular detection, respectively. As a result, the CoP-CoO/CC electrode only needs 210 mV overpotential to drive a current density of 10 mA cm−2 in an alkaline medium, superior to the most reported OER catalysts. Additionally, the CoP-CoO/CC also exhibits an ideal hydrogen evolution reaction response, and a water splitting system has been successfully constructed which can drive a 10 mA cm−2 within 1.65 V. This study supplies insight for catalytic origins p-p type heterojunctions OER catalyst, which provides a reference value for the efficient and reasonable design of heterojunction catalysts. [ABSTRACT FROM AUTHOR]

Developing efficient oxygen evolution reaction (OER) electrocatalysts with earth-abundant elements is very important for sustainable H 2 generation via electrochemical water splitting. Here we design a crystalline-amorphous Ni–Fe–Al hybrid phosphides nanosheet arrays grown on NiFe foam for efficient OER application. Dynamic surface reorganization of phosphides at anodic/cathodic polarizations is probed by in situ Raman spectroscopy. The reconstructed amorphous Ni(Fe)OOH species are determined as the active phases that facilitate the OER process. This unique electrode shows highly catalytic activity toward water oxidation, achieving the current densities of 10 and 100 mA cm−2 at 181 and 214 mV in 1 M KOH, respectively. Meanwhile, it also exhibits excellent stability at a large current density of 100 mA cm−2 for over 60 h. This work reveals the dynamic structural transformation of pre-catalyst in realistic conditions and highlights the important role of oxyhydroxides as real reactive species in OER process with high activity. [Display omitted] • Ni–Fe–Al hybrid phosphides nanosheet arrays were synthesized for OER. • Dynamic self-reconstruction was revealed by in situ Raman spectroscopy. • Amorphous Ni(Fe)OOH species act as the real active phases. • Regenerated pre-catalyst shows excellent OER activity. [ABSTRACT FROM AUTHOR]

Developing efficient and durable oxygen evolution reaction (OER) electrocatalysts with non-noble elements is particularly urgent for electrochemical water splitting. Herein, we report heterostructural Ni3S2–Fe5Ni4S8 hybrids directly grown on redox-NiFe foams (denoted as NFS/rNF) as excellent pre-catalysts for OER in 1 M KOH media. The electrochemical performance can be tuned by amount of sulfur source, and the optimized electrode only needs low overpotentials of 199 mV and 240 mV to attain 10 mA cm−2 and 100 mA cm−2, respectively. Moreover, the overpotential is further reduced to 231 mV to deliver 100 mA cm−2 after multi-cyclic voltammogram scans, due to the exposure of abundant in situ generated Ni(Fe)OOH species. Excellent stability with continuous 40 h operation is also demonstrated. Our study provides a new strategy for direct synthesis of self-standing integrated hybrid electrodes for efficient and durable water oxidation. [ABSTRACT FROM AUTHOR]

Rational design of high efficient and low cost oxygen evolution reaction (OER) electrodes is critical for electrochemical water splitting. Herein, we report Reevesite Ni−Fe layered double hydroxide (NiFe‐(CO32−)‐LDH) nanosheet arrays as novel OER catalysts in alkaline electrolyte. These self‐supported nanosheet arrays with a composition of Ni6Fe2(CO3)(OH)16 ⋅ 4H2O on Ni foam (NF) were synthesized by a one‐pot hydrothermal method, in which NF served as both the conductive substrate and Ni source. The morphology and OER activity can be tuned by iron concentration. In 1 M KOH, the optimized NiFe‐(CO32−)‐LDH catalyst only required overpotentials of 228 and 264 mV to deliver current densities of 10 and 100 mA cm−2, respectively, with a small Tafel slope of 37 mV dec−1. Remarkably, this catalyst also showed outstanding durability by long‐term operation for 20 h with 96 % retention. Our work provides attractive cost‐effective 3D catalysts for efficient and robust water oxidation at alkaline media. [ABSTRACT FROM AUTHOR]

Owing to the unique electronic properties, rare‐earth modulations in noble‐metal electrocatalysts emerge as a critical strategy for a broad range of renewable energy solutions such as water‐splitting and metal–air batteries. Beyond the typical doping strategy that suffers from synthesis difficulties and concentration limitations, the innovative introduction of rare‐earth is highly desired. Herein, a novel synthesis strategy is presented by introducing CeO2 support for the nickel–iron–chromium hydroxide (NFC) to boost the oxygen evolution reaction (OER) performance, which achieves an ultralow overpotential at 10 mA cm−2 of 230.8 mV, the Tafel slope of 32.7 mV dec−1, as well as the excellent durability in alkaline solution. Density functional theory calculations prove the established d–f electronic ladders, by the interaction between NFC and CeO2, evidently boosts the high‐speed electron transfer. Meanwhile, the stable valence state in CeO2 preserves the high electronic reactivity for OER. This work demonstrates a promising approach in fabricating a nonprecious OER electrocatalyst with the facilitation of rare‐earth oxides to reach both excellent activity and high stability. [ABSTRACT FROM AUTHOR]

Metal foams with high surface/volume ratio and excellent electrical conductivity are widely used in water splitting. Herein, we report a redox process sculpturing commercial NiFe foams with dual-scale porosities as high efficient catalysts for water oxidation reactions. Through the oxidation-reduction process, many pores of few micrometres in size were formed on a porous NiFe backbone with a pore size of 50–300 μm. The pore morphology can be reasonably controlled by varying the oxidation temperature. Electrochemical measurement demonstrates that redox-NiFe foam exhibits greatly enhanced activity towards oxygen evolution reaction. Specifically, the redox-NiFe foam oxidized at 900 °C yields the best catalytic activity with an overpotential of 294 ± 3 mV to achieve the current density of 100 mA cm−2 in 1 M KOH, which is much lower than 402 ± 2 mV of initial NiFe foam. This work highlights the formation of highly porous microstructure in the original skeleton of NiFe foam. Furthermore, the redox sculptured NiFe foams can also function as effective skeletons for the loading of active catalysts, which thus can find wide applications in electrocatalysis and energy storage. • NiFe foams with dual-scale porosities were fabricated by a redox process. • Micropore structure can be engineered by controlling oxidation temperature. • Redox-NiFe foams exhibited greatly enhanced water oxidation activity. • Redox NiFe foam showed excellent durability. [ABSTRACT FROM AUTHOR]

Interfacial engineering is an effective strategy for the design of active oxygen evolution electrode. Yet the intrinsic mechanism of heterogeneous interfaces remains largely unclear for the lack of direct evidence of real active phases. Herein, operando ultraviolet-visible (UV–vis) and Raman spectroscopies were used to probe the surface reconstruction behaviors of FeOOH@NiFe layered double hydroxides (LDH) hybrid catalysts, which revealed that FeOOH@NiFe LDH was converted into highly active FeOOH@ β-Ni(Fe)OOH phases during the OER process. The FeOOH-NiFe LDH interface can promote interfacial charge transfer, delay the Ni oxidation and induce the NiFe LDH phases to highly reactive β-Ni(Fe)OOH. The FeOOH@ β-Ni(Fe)OOH exhibited excellent OER performance (252 mV at 100 mA cm−2) and a 1.6 times increase (at overpotential of 300 mV) in turnover frequency (TOF) with respect to the active phase γ-Ni(Fe)OOH of NiFe LDH. This work clarifies that ration interface engineering can regulate the generation of highly active phases in the OER process. [Display omitted] • Reconstruction of FeOOH@NiFe LDH was study by operando UV–vis and Raman spectroscopies. • FeOOH induced the phase transformation of NiFe LDH to β-Ni(Fe)OOH at the interface. • The interfacial electric field of NiFe LDH and FeOOH promoted the charge transfer. • As-formed FeOOH@ β-Ni(Fe)OOH showed superior OER activity to γ-Ni(Fe)OOH. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) is a key step for electrochemical water splitting and understanding the surface reconstruction of OER pre-catalysts is of vital importance. Herein, hybrid Ni 5 P 4 @FeP nanosheet arrays were evaluated as promising OER pre-catalysts. The dynamic surface evolution was probed by in situ Raman spectroscopy, which revealed that Ni 5 P 4 @FeP was rapidly reconstructed to NiFe 2 O 4 during the anodic scan. The structural instability of amorphous NiFe 2 O 4 led to partial reconstitution to Ni/FeOOH at high oxidation potentials. As-formed Ni/FeOOH@NiFe 2 O 4 hybrid with high structural reversibility was established as a truly active species, which exhibited excellent alkaline OER performance with a low overpotential of 205 and 242 mV under current densities of 10 and 100 mA cm−2, respectively. This work provides a facile strategy to in situ construct an amorphous spinel/oxyhydroxide hybrid structure using electrochemical activation that holds strong promise for potential application in electrochemical water splitting and related energy devices. [Display omitted] • Surface reconstruction of Ni 5 P 4 @FeP was probed by in situ Raman spectroscopy. • Ni 5 P 4 @FeP was oxidized to NiFe 2 O 4 and further to Ni/FeOOH at high potentials. • The real active intermediate was identified as Ni/FeOOH and NiFe 2 O 4 hybrid. • High structural reversibility between NiFe 2 O 4 and Ni/FeOOH was found. • As-formed amorphous NiOOH and NiFe 2 O 4 hybrid showed superior OER activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe-Ni-S catalysts undergo surface self-reconstruction during alkaline electrocatalysis. • γ-NiOOH and metallic Ni act as reactive species for OER and HER, respectively. • Fe-Ni-S pre-catalysts show low overpotentials in OER and HER bifunctional activity. • An electrolyzer exhibits a cell potential of 1.55 V at 10 mA cm−2. Earth-abundant catalysts for both Oxygen evolution reaction (OER) and Hydrogen evolution reaction (HER) are highly required for electrochemical water splitting. Transition metal sulfides have been considered as efficient catalysts for both OER and HER, but their real active species in operation condition are still controversial. Herein, self-supported Ni 3 S 2 /FeNi 2 S 4 nanosheets (Ni-Fe-S) are synthesized and in-situ Raman measurement is conducted to monitor the phase transformation under realistic conditions. Combined with a series of ex-situ technologies, it can be concluded that, Ni-Fe-S nanosheets function as pre-catalysts which undergo dynamically structural reconstruction during electrolysis. The active species are determined to be γ-NiOOH for OER and metallic Ni0 for HER in 1 M KOH media, respectively. As-converted products only need overpotentials of 50 mV for HER and 201 mV for OER to achieve the current density of 10 mA cm-2, respectively. A two-electrode electrolyzer can afford a current density of 10 mA cm-2 at a low cell voltage of 1.55 V. This work provides new perspectives to recognize the catalytic evolution process of nickel-based sulfides for water splitting and sheds light on the rational design of bifunctional materials in energy devices. [ABSTRACT FROM AUTHOR]

Developing efficient and nonprecious electrocatalysts for oxygen evolution reaction (OER) is crucial for the hydrogen generation via water splitting. Here we report the direct growth of heterostructural Ni 2 P–Fe 2 P hybrid electrocatalysts on NiFe foams. The redox engineered NiFe foam (rNF) significantly enhances the OER performance. Among prepared catalysts, Ni 2 P–Fe 2 P/rNF performs the highest OER activity, driving the current densities of 10 and 100 mA cm−2 at low overpotentials of 218 and 270 mV in 1 M KOH, respectively. Meanwhile, it can maintain 100 mA cm−2 for 24 h without obvious degradation. The morphology and composition of NFP/rNF after OER test were carefully studied. This work suggests that self-supported bimetal phosphides of NFP/rNF is an efficient and durable electrode material for water oxidation. Heterostructural Ni2P-Fe2P hybrid electrocatalysts were direct grown on NiFe foams, which show excellent oxygen evolution activity and stability. Image 1 • The formation of micro-sized pores on the skeleton of NiFe foam (NF) substrate can enlarge surface area. • The heterogeneous Ni2P-Fe2P structure provides plentiful active sites for OER. • The Ni2P-Fe2P/ rNF foam exhibits an extraordinary electro catalytic performance. [ABSTRACT FROM AUTHOR]

Developing high-efficient and Earth-abundant electrocatalysts toward hydrogen evolution reaction (HER) is strongly desired for electrochemical water splitting but remains a considerable challenge. Herein, we propose a 3D hierarchical Fe(PO 3) 2 @Cu 3 P heterostructure nanotube arrays on Cu foams for promising HER catalysts. The HER performance can be tuned by changing FeCl 3 concentrations and the optimized cathode exhibits excellent HER activity in 1 M KOH with a low overpotentials of 108 mV @ 10 mA cm−2 and a small Tafel slope of 84 mV dec−1. Furthermore, this electrode delivers high electrochemical durability with stable operation for 24 h. Such high performance can be ascribed to the unique hierarchical heterostructure with large electrochemical surface area, synergistic effect and fast electron transport. Our study can provide new inspiration for rational construction of copper-based hierarchical nanomaterials for HER electrodes and other energy-related applications. Hierarchical Fe(PO 3) 2 @Cu 3 P nanotube hybrids on 3D copper foam were synthesized, which demonstrate excellent activity toward hydrogen evolution in alkaline solution with robust stability. Image 1 • Hierarchical Fe(PO 3) 2 @Cu 3 P nanotube arrays were successfully synthesized on Cu foam. • The hybrid catalysts exhibit excellent activities for HER in alkaline media. • Synergistic effect between Fe(PO 3) 2 and Cu 3 P was found by XPS. • The hybrid catalyst exhibits considerable stability for HER. [ABSTRACT FROM AUTHOR]