Modulating Carrier Kinetics in BiVO₄ Photoanodes through Molecular Co₄O₄ Cubane Layers

Understanding the role and immobilization of molecular catalysts on photoelectrodes is essential to use their full potential for efficient solar fuel generation. Here, a (Co4O4)-O-II cubane with proven catalytic performance and an active H2O-Co-2(OR)(2)-OH2 edge-site moiety is immobilized on BiVO4 photoanodes through a versatile layer-by-layer assembly strategy. This delivers a photocurrent of 3.3 mA cm(-2) at 1.23 V-RHE and prolonged stability. Tuning the thickness of the Co4O4 layer has remarkable effects on photocurrents, dynamic open circuit potentials, and charge carrier behavior. Comprehensive-time and frequency-dependent perturbation techniques are employed to investigate carrier kinetics in transient and pseudo-steady-state operando conditions. It is revealed that the Co4O4 layer can prolong carrier lifetime, unblock kinetic limitations at the interface by suppressing recombination, and enhance charge transfer. Additionally, its flexible roles are identified as passivation/hole trapping/catalytic layer at respective lower/moderate/higher potentials. These competing functions are under dynamic equilibrium, which fundamentally defines the observed photocurrent trends.