Synthesis of an in situ core–shell interlink ultrathin-nanosheet Fe@FexNiO/Ni@NiyCoP nanohybrid by scalable layer-to-layer assembly strategy as an ultra-highly efficient bifunctional electrocatalyst for alkaline/neutral water reduction/oxidation

One of the tremendous challenges for industrially profitable water electrolysis by a more economically viable electrochemical approach is to exploit earth-abundant and ultra-efficient bifunctional (pre)electrocatalysts. Herein, a scalable layer-to-layer assembly strategy is first proposed to delicately construct in situ core–shell Fe@FexNiO nanosphere interlink ultrathin Ni@NiyCoP nanosheet nanohybrids on Ni-foam via controllable two-step electrodeposition pathway. By deliberately introducing metallic Fe and Ni into amorphous FexNiO/NiyCoP nanoclusters serving as the everlasting-conductivity and attached-active-sites along with morphological controls, Fe@FexNiO/Ni@NiyCoP nanohybrids achieved ultralow overpotentials of 92 and 270 mV at 100 mA cm−2 for the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with uncompromising long-term durability for 100 h in 1 M KOH alkaline-electrolyte, respectively, and was even superior to the Pt plate and RuO2 at larger current density (ηOER = 400 mV, ηHER = 129 mV at 1500 mA cm−2). Besides, it also exhibited wonderful catalytic activity in 1 M phosphate-buffer-solution (PBS, pH = 7), achieving a cell-voltage of 1.86 V at 10 mA cm−2. The metallic Ni bonding amorphous NiyCoP was recognized as high-intrinsic HER activity, whereas the Fe@FexNiO coupling in situ newly generated NiCoOOH species on the Ni@NiyCoP surface-layer was identified as intrinsic OER active-matter. Synergistic effects between Fe@FexNiO and Ni@NiyCoP further accelerated the water-splitting dynamics. Impressively, the bifunctional Fe@FexNiO/Ni@NiyCoP/NF achieves an alkaline cell-voltage of 1.43 V at 10 mA cm−2, representing the best bifunctional material hitherto, which is promising for the scale-up commercialization of the production.