Triple hierarchy and double synergies of NiFe/Co ₉ S ₈ /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 Co ₉ S ₈ nanotubes as the intermediate layer, and NiFe hydroxide as the top layer, resulting in two synergistic effects between Co ₉ S ₈ and CC, and NiFe and Co ₉ S ₈ . 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.