Single-Nanoentity Visualization of Cation- and pH-Dependent Structural Evolution of CoOOH during Oxygen Evolution Reaction

Abstract Cobalt oxyhydroxide (CoOOH) serves as a key active species for driving the oxygen evolution reaction (OER). Nevertheless, the dynamic structural evolution of CoOOH during OER and its response to electrolyte environments remain insufficiently understood at the single-nanoentity level. Herein, we demonstrate a high-spatiotemporal-resolution optical imaging strategy to achieve in situ visualization and dynamic tracking of structural reconstruction behaviors of single CoOOH nanosheets during OER. A cation-dependent reaction regulatory mechanism is systematically uncovered, demonstrating that alkali metal cations (Li+, Na+, K+) in electrolytes distinctly modulate the kinetics of CoOOH nanosheets. Furthermore, electrolyte pH is verified as a critical regulatory factor dominating the structural response characteristics of the electrochemical catalyst. Alkaline environments promote the structural transition of CoOOH at reduced oxidation potentials, neutral electrolytes support rapid and reversible interfacial electron transfer, whereas acidic conditions impose unfavorable thermodynamic restrictions to impede catalyst structural reconstruction. This work clarified the cation and pH dual-dependent structural evolution mechanism of CoOOH electrocatalysts, offering fundamental insights and rational design principles for the development of high-efficiency cobalt-based OER electrocatalysts adaptable to multi-pH electrochemical systems.