Operando Probing of Charge Transfer at the Semiconductor/Cocatalyst/Solution Interface in Photoelectrocatalytic Water Oxidation

/CoOOH interface and enhancing the system photovoltage. Further tracking charge transfer to the solution, we find that CoOOH increases the water oxidation rate constant by a factor of 1.8 at surface potentials below the thermodynamic water-oxidation potential, corresponding to a population-controlled regime. More importantly, at surface potentials above the water-oxidation potential, CoOOH induces a transition to a Butler-Volmer-controlled regime, in which water oxidation is catalyzed with an exponentially increasing rate constant. These findings provide fundamental understanding and mechanistic insights into the role of cocatalysts in facilitating charge transfer across multiple interfaces during PEC operation.