One-Step Fabrication of Monolithic Electrodes Comprising Co₉ S₈ Particles Supported on Cobalt Foam for Efficient and...

A very easy and cost-effective approach to the fabrication of monolithic Co₉ S₈ water oxidation electrodes (Co@Co₉ S₈ ), fabricated by one-step hydrothermal treatment of commercially available cobalt foam in the presence of thiourea, is reported. The morphology, crystal structure, microstructure, and composition of as-fabricated Co@Co₉ S₈ electrodes were examined by using scanning electron microscopy (SEM), powder X-ray diffractometry (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS), and their electrochemical properties were investigated by cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). When used to catalyze the oxygen evolution reaction (OER) in alkaline solution, the Co@Co₉ S₈ electrode with an optimal Co₉ S₈ loading exhibits outstanding catalytic activity, requiring a low overpotential of 350 mV to deliver an anodic current density of 10 mA cm^-2 and showing fast kinetics for OER with a small Tafel slope (55 mV dec^-1 ) and charge-transfer resistance (0.44 Ω cm^-2 ), which outperforms many sulfide-based OER catalysts and some state-of-the-art noble metal catalysts recently reported in the literature. Importantly, the electrodes show excellent long-term stability, and are capable of operating at both a low current density and a high current density relevant to industrial water electrolysis up to 100 hours.