OER monitoring and kinetics at pH 14. Other than for the operando spectroscopic monitoring of the HER, we have also implemented operando time-resolved XAS and Raman characterizations to unveil the dynamics of active species and sites of o-CoSe2 for the OER at pH 14 (Figure and Figures and). Analysis of the operando time-resolved Co Kedge XANES spectra (Figure ) shows that the white line signatures of the dipolar transitions from Co 1s to 4p hybridized orbitals display profile changes toward higher energy positions and enhanced signal intensities, inferring the oxidations of Co centers and the formation of Co-based oxides/hydroxides. An in-depth analysis of the operando time-resolved Co K-edge XAS data reveals that the Co valence state reaches its maximum value of ca. +2.70 at 1.5 V vs. RHE, while a slight decrease can be observed after the removal of the applied potential. This corroborates that the OER relies on the in situ generated catalytically active high-valent Co species, in agreement with many previous studies. The local coordination environments of Co centers in o-CoSe2 for the OER were investigated through operando time-resolved Co K-edge EXAFS and FT-EXAFS spectra monitoring(Figure , Figures and, and Table ). Our operando timeresolved monitoring reveals that o-CoSe2 undergoes potentialdriven restructuring into defective CoO2 species, which is a prerequisite to initiating the OER at pH 14. The crucial formation of the high-valent CoO2 species derived from o-CoSe2 during the OER can be also evident from operando Raman spectra characterizations (Figure ). As expected, during the alkaline OER, the characteristic Se-Se librational vibration signals feature drastic profile changes and are barely detected when the applied potentials are higher than 1.3 V vs. RHE. In sharp contrast, with the anodic polarizations, two newly formed vibration features at ca. 468 and 568 cm -1 , which are associated with CoO2 species, were first observed at 1.3 V vs. RHE, and then they exhibit profile changes towards higher signal intensities as the potentials increased. This is a piece of evidence to support that the in situgenerated high-valent CoO2 species is the key to the O2 release in o-CoSe2. It is also noteworthy that the operando Raman spectra of o-CoSe2 only feature v(SeOx -) signals below 1.3 V vs. RHE. Such vibration signals are barely detected in the OER region (Figure ). Moreover, after the removal of the potential, a remarkable v(SeO4 2-) signal in the post-catalytic electrolytes can be observed, suggesting that the surface oxidized anionic components in o-CoSe2 undergo complete leaching into the electrolytes (Table ), which is not decisive to the OER. ) also unveil that the surface oxidized oxyanions (i.e. SeO4 2-or SO4 2-) in c-CoSe2 and c-S-CoSe2 are completely leached into the electrolyte during the OER. However, the open question of whether trace amounts of the oxidized anionic residual play a role in the OER still needs to be elucidated. This open question can be well addressed by conducting the OER characterizations of partially Pincorporated o-CoSe2 (o-P-CoSe2) (Figures and). This is because heteroatom doping has been demonstrated as an effective strategy to tune the OER kinetics of the catalysts. As shown in Figure , no significant difference in the activity is observed between o-CoSe2 and o-P-CoSe2. Additionally, the post-catalytic Raman spectra clearly corroborate that the as-investigated o-P-CoSe2 completely converts into CoOOH-like species without any oxidized anionic residual absorbed on the surface. This strongly supports that the surface oxidized oxyanions in CoSe2 catalysts are not the key to initiating the OER. On the other hand, operando XAS results (Tables S5, S6, and S9) unambiguously unravel that the in situ restructured catalytically OER active species (i.e. CoO2) derived from the as-investigated CoSe2 catalysts feature significant structural disorder. As reported, engineering defective catalysts generally offer abundant active sites, thereby regulating the desorption/adsorption of key OER intermediates. As a result of the tuned OER kinetics, employment of transition metal non-oxide catalysts enables a better OER performance compared to conventionally synthesized oxides.