Surface evolution of an amorphous iron selenide-bridged nickel selenide (NiSe2) heterointerface enabling robust alkaline water splitting

Constructing highly active and robust bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is crucial for overall water splitting. Herein, a hierarchical heterostructure is designed via a simple two-step electrodeposition process, in which an amorphous iron selenide (FeSe x ) layer bridges the catalytically active NiSe 2 layer and the NF substrate (FeSe x -NiSe 2 /NF). The surface oxidation of NiSe 2 results in the incorporation of SeO x species. The resulting NiSe 2  + SeO 4 surface provides effective active sites, thereby kinetically favoring the HER process. During OER, the surface NiSe 2 reconstructs into a γ-NiOOH phase, which serves as the catalytically active phase for OER. As a consequence, the FeSe x -NiSe 2 /NF electrode requires only 146 mV (HER) and 340 mV (OER) to deliver a current density of 500 mA cm −2 , while maintaining stable operation at this current density for 100 h. These findings offer insights into the superior catalytic performance of the hierarchical FeSe x -NiSe 2 /NF heterostructure, which is expected to foster the rational development of bifunctional electrocatalysts. Download: Download high-res image (421KB) Download: Download full-size image