Boosting the Electrochemical Water Splitting on Co3O4 through Surface Decoration of Epitaxial S-doped CoO Layers

Highly efficient and cost-effective electrocatalysts towards both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are critical for the large-scale and environmental-friendly hydrogen production. Here we report the facile synthesis of a novel bifunctional catalyst, mesoporous Co3O4 with surface decorated epitaxial S-doped CoO layers (S-CoO/Co3O4), via a simple solution-combustion and thioacetamide-sulfidation method. S-CoO/Co3O4 shows excellent electrochemical catalytic activity and stability in 1 M KOH with small overpotentials of 275 mV for OER and 181 mV for HER at 10 mA cm(-2) on a rotating disk electrode. Moreover, when loaded on nickel foam and used as both cathode and anode for overall water splitting, the current density reaches 10 mA cm(-2) at a relatively low voltage of 1.60 V and degrades for only similar to 5.7% after 20 h operation. The excellent electrochemical performance is mainly attributed to the highly active surface S-doped CoO species, which also acts as the protective buffer layer for the inner bulk phase and results in enhanced stability. Density functional theory calculations show that the S-doping in CoO and Co3O4 can accelerate the carrier transport, promoting the overall electronic conductivity and electrochemical catalytic activity.