Clearly, the multielectron transfer OER holds the key to developing effective overall water-splitting electrocatalysts. Note that L-CoS exhibited very poor catalytic activity and was unstable for the OER in 0.5 M H2SO4 (Figure ). Therefore, the following discussion of the as-prepared sulfide catalysts will be only focused on the OER characterization in 1 M KOH. As shown in Figure and Figure , to achieve a current density of 0.05 mA/cmECSA 2 and 10 mA/cmgeo. , a minimum overpotential of 348 and 300 mV is essential for L-CoS, respectively, which outperformed those of reference Co-LDH (402 and 338 mV) and Co3O4-ZIF (384 and 387 mV). Similar to the electrochemical HER characterization, the OER characterizations of highly crystalline sulfide catalysts were also performed at pH 14 (Figure ). Note that there is no obvious activity change between L-CoS and highly crystalline sulfide catalysts (Figure ), reflecting that they involved similar OER kinetics. Further analysis of CV results (Figures ) showed that all sulfide catalysts underwent irreversible structural rearrangement during the OER.