Hybridized heterostructure of CoS and MoS2 nanoparticles for highly-efficient and robust bifunctional water electrolysis

• CoS/MoS 2 heterostructure nanoparticles are fabricated using a single–step hydrothermal process. • Excellent bifunctional activities along with long-term sustainability in 1 M KOH electrolyte. • Low OER (229 mV) and HER (74 mV) overpotentials at 10 mA cm ─2 with small Tafel slopes are achieved. • DFT calculations reveal that one–way electron transfer activates both oxidative/reductive reactions. For industrial hydrogen production, it is beneficial to develop highly-efficient, earth-abundant, and bifunctional electrocatalysts which exhibit compatibility between oxygen evolution reaction (OER) or hydrogen evolution reaction (HER) activity and stability in the same electrolyte. Herein, we report a bifunctional hybrid CoS/MoS 2 nanoparticle electrocatalyst in 1 M KOH, fulfilling desirable industrial criteria for water electrolysis. The CoS/MoS 2 catalyst exhibits excellent OER and HER activities with very low overpotentials as well as outstanding stability for more than 100 h, even at a high current density of 250 mA cm −2 . The bifunctional CoS/MoS 2 catalyst-based water-electrolyzer exhibits a low cell voltage of 1.52 V at 10 mA cm −2 (1.714 V at 100 mA cm −2 ) with long–term stability. Density functional theory calculations reveal that the hybrid CoS/MoS 2 electrocatalyst shows one–way electron transfer that can activate both oxidative/reductive reactions. Therefore, it exhibits superior OER and HER activities, outperforming the state-of-the-art noble-metal-free catalysts.