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

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.