Crystalline FeNiCoP _<i>x</i> Nanoparticles Dispersed into an Amorphous FeNiCoO _<i>x</i> Matrix as a Bifunctional Electrocatalyst for Ampere-Level Current Density

Amorphous–crystalline interfaces are one of the most favorable designs for improved oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), as interfaces offer enhanced and variable catalytic centers. Herein, an efficient and robust bifunctional electrocatalyst, FeNiCoP x /FeNiCoO x /NF, is reported with amorphous–crystalline interfaces synthesized by integrating nanocrystalline FeNiCoP x with amorphous FeNiCoO x sheets evolved on nickel foam having a two-step controlled hydrothermal-phosphidation process. The FeNiCoP x /FeNiCoO x /NF demonstrated excellent OER and HER activity having overpotentials of ∼220 and 120 mV to reach 100 mA cm –2 current density having small Tafel slopes of 42 and 75 mV dec –1, respectively. This also adequately worked for seawater electrolysis. Bifunctional FeNiCoP x /FeNiCoO x /NF was assembled in an alkaline seawater electrolyzer, an ampere-level current density was achieved at a cell potential of 2.06 V, placing it among the most effective seawater electrocatalysts. Experimental and theoretical investigations revealed a strong coupling between nanocrystalline FeNiCoP x particles and amorphous FeNiCoO x nanosheets via alteration of d-band centers. The synthetic strategy and crystalline–amorphous interface regulations in this work provide directions for constructing highly efficient and stable bifunctional electrodes for commercial alkaline water electrolysis.