Crystalline‐Amorphous Ni2P4O12/NiMoOx Nanoarrays for Alkaline Water Electrolysis: Enhanced Catalytic Activity via In Situ Surface Reconstruction

Water electrolysis affords a promising approach to large‐scale hydrogen yield, but its efficiency is restrained by the sluggish water dissociation kinetics. Here, an efficient bifunctional electrocatalyst of in situ formed crystalline nickel metaphosphate on amorphous NiMoOx nanoarrays supported on nickel foam (c‐Ni2P4O12/a‐NiMoOx/NF) for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution is reported. The c‐Ni2P4O12/a‐NiMoOx/NF can deliver a current density of 10 mA cm–2 at a low potential of 78 mV for HER, and a current density of 20 mA cm–2 at an overpotential of 250 mV for OER. Moreover, it only requires a small cell voltage of 1.55 V at 10 mA cm–2 for robust water splitting with outstanding long‐term durability over 84 h. Various spectroscopic studies reveal that in situ surface reconstruction is crucial for the enhanced catalytic activity, where c‐Ni2P4O12/a‐NiMoOx is transformed into c‐Ni2P4O12/a‐NiMoO4 during the HER process, and into c‐Ni2P4O12/a‐NiOOH in the OER process. This work may provide a new strategy for uncovering the catalytic mechanism of crystalline‐amorphous catalysts. The crystalline‐amorphous Ni2P4O12/NiMoOx nanoarrays, undergo in situ surface reconstruction during the hydrogen evolution reaction and oxygen evolution reaction processes, are highly efficient for alkaline water electrolysis.