Improved Catalytic Activity and Stability of Co₉S₈ by Se Incorporation for Efficient Oxygen Evolution Reaction

Combining an excellent electrocatalytic activity with the good structural stability of Co₉S₈ remains challenging for the oxygen evolution reaction (OER). In this study, density functional theory was used to demonstrate the importance of moderate adsorption strength with *O and *OOH intermediate species on Co₉S₈ for achieving excellent electrocatalytic performances. A novel strategy was proposed to effectively optimize the *O oxidation to *OOH by introducing Se heteroatoms to adjust adsorption of the two intermediates. This process also allowed prediction of the simultaneous enhancement of the structural stability of Co₉S₈ due to the weak electronegativity of a Se dopant. The experimental results demonstrated that Se doping can regulate the charge density of Co²⁺ and Co³⁺ in Co₉S_8-Se, leading to a substantially improved OER performance of Co₉S_8-Se. As a result, our Co₉S_6.91Se_1.09 electrode exhibited an overpotential of 271 mV at 10 mA cm^-2 in a 1.0 M KOH solution. In particular, it also demonstrated an excellent stability (∼120 h) under a current density of 10 mA cm^-2, indicating the potential for practical applications. Overall, the proposed strategy looks promising for regulating the electronic structures and improving the electrochemical performances of sulfide materials.