Triple hierarchy and double synergies of NiFe/Co9S8/carbon cloth: a new and efficient electrocatalyst for the oxygen evolution reaction

Abstract

Electrochemical water splitting requires an efficient water oxidation catalyst to accelerate the oxygen evolution reaction (OER). A triple hierarchy catalyst structure based on abundant transition metals in soil (Fe, Co, and Ni) was prepared via chemical bath deposition, followed by a hydrothermal and electrodeposition method for the high-efficiency OER. The obtained electrode consisted of a three-layer porous structure, with a carbon cloth (CC) substrate as the bottom layer, vertically aligned Co₉S₈ nanotubes as the intermediate layer, and NiFe hydroxide as the top layer, resulting in two synergistic effects between Co₉S₈ and CC, and NiFe and Co₉S₈. This layered structure contained no binder, which facilitated catalytic site exposure, enhanced electron transfer, and accelerated the dissipation of gases generated during the catalytic process. This triple hierarchy multimetal/carbon electrode exhibited remarkable OER activity in an alkaline medium with a small overpotential of 219 mV (vs. RHE) at 10 mA·cm⁻² and low Tafel slope of 55 mV·dec⁻¹. Furthermore, this triple hierarchy electrode was stable for up to 20 h. The prepared triple hierarchy polymetallic material can be considered to be among the most promising oxygen evolution catalysts.