Hierarchical Selenium-Doped Nickel–Cobalt Hybrids on Carbon Paper for the Overall Water-Splitting Electrocatalytic System

Designing and constructing hierarchically structured materials with heterogeneous compositions is the key to developing an effective catalyst for overall water-splitting applications. Herein, we report the fabrication of hollow-structured selenium-doped nickel-cobalt hybrids on carbon paper as a self-supported electrode (denoted as Se-Ni|Co/CP, where Ni|Co hybrids consist of nickel-cobalt alloy-incorporated nickel-cobalt oxide). The procedure involves direct growth of zeolitic imidazolate framework-67 (ZIF-67) on bimetal-based nickel-cobalt hydroxide (NiCoOH) electrodeposited on CP, followed by selenous etching and pyrolysis to obtain the final Se-Ni|Co/CP electrocatalytic system. The optimized Se-Ni|Co/CP [Se-Ni₁|Co₉/CP(0.3)] exhibits remarkable performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), displaying a current density of 10 mA cm^-2 at small overpotentials of 105 mV for HER and 235 mV for OER. Furthermore, it allows an alkali electrolyzer to achieve a current density of 10 mA cm^-2 at a cell voltage of only 1.51 V. The outstanding catalytic activity of Se-Ni|Co/CP is ascribed to the high intrinsic activity of the bimetallic catalyst, efficient interfaces, and charge transport facilitated by the heterogeneous component, the hollow structure inherited from the metal-organic frameworks (MOF)-derived material providing ample porosity and active sites, and structural robustness achieved through self-supported construction.