Improved Catalytic Activity and Stability of Co 9 S 8 by Se Incorporation for Efficient Oxygen Evolution Reaction.

Combining an excellent electrocatalytic activity with the good structural stability of Co 9 S 8 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 Co 9 S 8 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 Co 9 S 8 due to the weak electronegativity of a Se dopant. The experimental results demonstrated that Se doping can regulate the charge density of Co 2+ and Co 3+ in Co 9 S 8- x Se x , leading to a substantially improved OER performance of Co 9 S 8- x Se x . As a result, our Co 9 S 6.91 Se 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.