The underlying structural kinetics and the nature of active species of highly crystalline CoS2, CoS, Co3O4-ZIF, and Co-LDH before and after the catalytic reactions in different media were also evaluated by ex situ XAS characterizations (Figures ). The following conclusions can be drawn from our observations: (i) highly crystalline CoS2 and CoS show similar structural changes in the local electronic structure and coordination environments of Co centers before and after electrolysis in different media compared to those of L-CoS (Figures ), namely, a) structural integrity is well retained after the acidic HER, b) HER at pH 14 induces a local geometric rearrangement into S-Co-O-Co-S moieties, c) generation of CoOOH-related species is the prerequisite for the OER at pH 14. These observations highlight that restructuring is a common phenomenon existing in sulfide-related catalysts and that the level of restructuring is strongly dependent on the working pH conditions. (ii) Co-LDH shows structural changes after the OER, while the production of H2 will not alter its initial structure, demonstrating that the oxidations or the applied potentials emerge as critical parameters to initiate the structural rearrangement of the catalysts; (iii) Co3O4-ZIF maintains its initial spineltype structure before and after electrolysis in different media, suggesting that oxide-type catalysts often show high kinetic barriers for realizing their restructuring into active species.