To gain in-depth insights into the origins of the intrinsic catalytic activities and the underlying structural kinetics of CoSe2 catalysts in different media, we first performed ex situ XPS characterizations for the catalysts before and after water electrolysis [Note: In this study, "post-catalytic characterization" refers to samples subjected to electrochemical stability tests, as shown in the durability measurements in Figure . From the results (discussion details in Figures ), except for o-CoSe2, the investigated CoSe2 catalysts remain stable for the HER at both pH 0 and 14, while after the OER all catalysts undergo complete surface restructuring into oxide/hydroxide species without any prominent oxidized anionic components adsorbed on the surface. To precisely identify the true catalytically active species and to establish an identical structure-activity relationship during the water electrolysis process, operando time-resolved XAS and Raman spectra characterizations were further carried out.