Hydrothermal Synthesis of Co-MoS₂ as a Bifunctional Catalyst for Overall Water Splitting

The sluggish kinetics of the oxygen evolution reaction is the main obstacle to the development of water splitting. MoS₂ exhibits excellent activity in hydrogen evolution reaction (HER). However, the catalytic activity is insufficient for commercial bifunctional catalysts due to the inadequate oxygen evolution reaction (OER) catalytic activity. To address the deficiency of the OER active site of MoS₂ and develop a more effective bifunctional catalyst, a one-step hydrothermal process was employed to synthesize a nonprecious Co-MoS₂ catalyst, utilizing sodium molybdate as the molybdenum source, thiourea as the sulfur source, and cobalt nitrate as the cobalt source, respectively. The electrocatalytic activity of the sample was tested in an electrolyte solution of 0.1 M KOH and 1 M KOH. The experimental result indicated that the catalytic activity of the Co-MoS₂ catalyst for HER and OER was remarkably enhanced compared to the pristine MoS₂. The overpotential of OER and HER was reduced by approximately 200 mV and 130 mV in a 0.1 M KOH solution, respectively. Additionally, in the 1 M KOH electrolyte, the overpotentials of OER and HER were about 312 mV and 297 mV, respectively. Co-MoS₂ with the Co(NO₃)₂ doping of 0.6 g (0.206 mol %) also exhibited excellent stability in 0.1 M KOH and 1 M KOH electrolytes. When the Co-MoS₂ (Co(NO₃)₂-0.6 g, 0.343 mol %) electrode was used as both anode and cathode for overall water splitting in the 1 M KOH electrolyte, the current density of 10 mA cm^-2 could be achieved with only 1.86 V and with a good stability. This work provides an alternative for bifunctional catalysts in overall water splitting.