Antagonism effect of residual S triggers the dual-path mechanism for water oxidation

Transition metal chalcogenides (TMCs) are recognized as pre-catalysts, and their (oxy)hydroxides derived from electrochemical reconstruction are the active species in the water oxidation. However, understanding the role of the residual chalcogen in the reconstructed layer is lacking in detail, and the corresponding catalytic mechanism remains controversial. Here, taking Cu1−xCoxS as a platform, we explore the regulating effect and existence form of the residual S doped into the reconstructive layer for oxygen evolution reaction (OER), where a dual-path OER mechanism is proposed. First-principles calculations and operando 18O isotopic labeling experiments jointly reveal that the residual S in the reconstructive layer of Cu1−xCoxS can wisely balance the adsorbate evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM) by activating lattice oxygen and optimizing the adsorption/desorption behaviors at metal active sites, rather than change the reaction mechanism from AEM to LOM. Following such a dual-path OER mechanism, Cu0.4Co0.6S-derived Cu0.4Co0.6OSH not only overcomes the restriction of linear scaling relationship in AEM, but also avoids the structural collapse caused by lattice oxygen migration in LOM, so as to greatly reduce the OER potential and improved stability.