The role of selenium vacancies in the enhancement of electrocatalytic activity of CoNiSe2 for the oxygen evolution reaction

The chemical engineering of chalcogens' defects (either selenium or sulfur) on the surfaces of Nonprecious transition metal chalcogenides provides an effective route to enhance their electrocatalytic activity. Yet, the precise role of such defects during the OER is not fully understood, which in turn precludes an efficient optimization of their catalytic activity. Herein, CoNiSe2 film, representing a multi-transition metal selenide model with selenium defects, is electro-deposited on a carbon cloth to investigate and optimize the intrinsic and dynamic behavior of selenium vacancies during the OER process. Interestingly, the defective CoNiSe2 with the optimized amount of selenium vacancies exhibits an advanced OER performance, including low overpotential (252 mV at 10 mA cm-2) and high stability for 30 h. The ex-situ XPS and Raman spectroscopies also indicate that the optimized amount of selenium vacancies can facilitate the pre-oxidation of Co and Ni sites. The latter leads to a rapid adsorption of OH- ions and a further stabilization of Co/NiOOH, which in turn mediates the efficiency of OER. The density functional theory (DFT) calculations show that the introduction of a Se-vacancy on CoNiSe2 surface enables to adjust the changes in Gibbs free energy between different OER steps and thereby, significantly reduce the overpotential.