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The pursuit of efficient and stable electrochemical catalysts based on transition metals (TMs) for the hydrogen evolution reaction (HER) is of paramount importance. Herein, a novel partially amorphous NiMoB/NiMoO 4−x catalyst with dense nanoparticle assemblies has been prepared with B doping and reduction by one step NaBH 4 treatment of smooth nanorod-like NiMoO 4 precursor. Benefiting from the MoNi 4 alloys partially reduced from NiMoO 4 precursor, optimized electronic state through B doping and partially amorphous structure, NiMoB/NiMoO 4−x obtained splendid activity for HER with a lower overpotential of 26.2 mV at 10 mA cm 2 coupled with a narrow Tafel slope of 66.75 mV dec 1, in contrast to NiMoO 4 precursor catalyst (260.24 @10 mA cm 2, 149 mV dec 1) in alkaline solution. Additionally, the self-supported NiMoB/NiMoO 4−x electrode exhibits remarkable stability, maintaining a current density of 50 mA cm 2 for a minimum of 40 h attributed to mixed phases of MoNi 4 and amorphous NiMoO 4−x for accelerating the H 2 evolution and enhancing water adsorption. This work offers a facile avenue to rationally design high-performance electrocatalysts for enhancing hydrogen evolution with NaBH 4 accompanying borate doping and reduction. [Display omitted] • Partially amorphous NiMoB/NiMoO 4−x was constructed by one step hydrothermal. • MoNi 4 alloys accelerate H 2 evolution assisted by amorphous NiMoO 4−x. • Oxygen vacancies (O v) can enhance the conductivity and hydrogen spillover effect. • B doping effectively modulates the electronic structure of NiMoB/NiMoO 4−x. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are considered as considerable candidate for electrocatalytic water splitting. The main holdback locates in fabricating well-defined HEAs with moderate electronic structure and uncovering the structural evolution during the reaction process. Herein, we successfully synthesized NiCoFeCrMo HEA-nps by an ultrafast joule heating method for highly efficient oxygen evolution reaction (OER). The optimal graphene incorporated NiCoFeCrMo HEA nanoparticles (HEA-nps) exhibits finely distributed nanoparticles with average size of 17.49 nm and uniformly distribution of all the five elements, which displays the outstanding OER performance with a low onset potential and only requires the 260 mV (vs RHE) to achieve the current density of 10 mA cm−2. X-ray absorption fine structure (XAFS) demonstrates that the high valence Cr and Mo can directly regulate the local structure of HEA-nps, which significantly promoted the intrinsic activity of high active species. This work not only provides a design strategy related to the high valence elements injection for HEAs, but also uncovers the structural evolution of HEAs during OER process. [Display omitted] • NiCoFeCrMo HEA were successfully synthesized by fast Joule heating method. • Multi-electron Cr and Mo elements have regulated the local electronic structure. • The intrinsic mechanism of each element in HEAs during the reaction process has been clarified. [ABSTRACT FROM AUTHOR]