Metallic selenium as novel bifunctional electrocatalysts for highly efficient overall water electrolysis

Transition metal chalcogenides (TMCs) have been considered as potential materials for catalytic applications as efficient, stable, and non-precious electrocatalysts. However, most of significant progress has been made by focusing primarily on transition metal cations of electrocatalytic materials, while chalcogen anions with various redox chemical valences suitable for the water electrolysis process have received little attention. Herein, for the first time, we present metallic selenium (M-Se) as electrocatalytic materials for water electrolysis. M-Se is synthesized through pH manipulation by a facile hydrothermal synthesis approach. We demonstrate that the M-Se electrocatalyst can reach a current density of 50 mA cm⁻² with a low overpotential of 217, 242, and 444 mV for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and full cell water splitting, respectively, in alkaline electrolyte. Moreover, we further demonstrate the excellent stability of the M-Se electrode, which retain a current density of 50 mA cm⁻² over long-term continuous tests (24 h) with negligible variation in overpotential.