OER monitoring and kinetics at pH 14. We further characterized the structural and OER kinetics of L-CoS by performing operando XAS at pH 14 (Figure and Figures ). Specifically, analysis of operando XANES (Figure and) spectra shows that the dipolar transition contributions from Co 1s to Co 3d-S 2p hybridized orbitals are immediately diminished when the applied potential was higher than 0.9 V vs. RHE, while the signal intensity of the fingerprints of Co 1s to Co 3d-O 2p hybridized orbital transitions gradually increased as a function of the applied potential. This demonstrates that L-CoS undergoes a thorough sulfur-oxygen exchange reaction before the OER. An in-depth mechanistic investigation into the variations of Co valence state and the changes of the local coordination environments of Co centers (Figure , and Table ) suggests that L-CoS undergoes the following restructuring processes during the OER: (i) with the anodic polarization, a sulfur-exchange reaction generates CoOOH-related species in L-CoS; (ii) entire structural conversion from L-CoS to CoOOH is completed at 1.0 V vs. RHE; (iii) from 1.0 to 1.2 V vs. RHE, CoOOH intermediates undergo potential-driven structural optimization to achieve a 6-fold Co-O coordination; (iv) a potential-dependent deprotonation reaction in CoOOH generates the catalytically active CoO2 intermediates above 1.325 V, and the Co valence state reaches a maximum value of +3.3 at 1.52 V; (v) after removing the applied potential, a slight decrease in the Co valence state corroborate its redox reversibility during the OER.