Maximizing oxygen vacancy content via Ni/Mo/S triple-doping and electrochemical surface reconstruction for highly...

Developing highly active and stable catalysts for oxygen evolution reaction (OER) is crucial for advancing water splitting technologies, in which the oxygen vacancy (O_v) has been identified as a key factor influencing electrochemical activity. To elucidate the impact of O_v content on the adsorption process of oxygen-containing intermediates and catalytic performance, NiOOH-loaded carbon cloth (CC) electrodes with varying O_v contents were synthesized through a combination of hydrothermal treatment, low-temperature sulfurization, and electrochemical surface reconstruction. Density functional theory (DFT) simulations revealed that an increase in O_v content induced a positive shift in the valence band center of Ni 3d orbitals, which enhanced the number of bonding electrons and consequently improved the adsorption capacity for oxygen-containing intermediates. Moreover, the change of Gibbs free energy (ΔG) of the OER rate-determining step progressively decreased as O_v content increased, ultimately altering the rate-determining step from the dehydrogenation of hydroxyl intermediates (*OH) to the formation of peroxide intermediates (*OOH). Among the electrodes, the NiMo₃S₄/NiOOH@CC electrode, exhibiting the highest relative O_v content of 60.3% (absolute content of 24.9%), demonstrated superior catalytic performance characterized by a low overpotential (207 mV at 10 mA cm^-2), a small Tafel slope (57 mV dec^-1), a low charge transfer resistance (2.5 Ω), and a long stability (27.7 h), outperforming other NiOOH-loaded electrodes with lower O_v contents. This work elucidated the mechanistic role of O_v content in OER and provided valuable insights for the design and development of transition metal oxyhydroxide-based electrodes.