Directional Charge Transfer Channels in a Monolithically Integrated Electrode for Photoassisted Overall Water Splitting

Photoelectrocatalytic performance of a system is fundamentally determined by the full absorption of sunlight and high utilization of photoexcited carriers, but efficiency of the latter is largely limited by inefficient charge transfer from the absorber to reactive sites. Here, we propose to construct directional charge transfer channels in a monolithically integrated electrode, taking carbon dots/carbon nitride (CCN) nanotubes and FeOOH/FeCo layered double hydroxide (FFC) nanosheets as a representative, to boost the photoassisted overall water splitting performance. Detailed experimental investigations and DFT calculations demonstrate that the interfacial C-O-Fe bonds between CCN and FFC act as charge transfer channels, facilitating the directional migration of the photogenerated carriers between CCN and FFC surfaces. Moreover, the in situ oxidized Fe/Co species by photogenerated holes trigger lattice oxygen activation, realizing the construction of the Fe-Co dual-site as the catalytic center and efficiently lowering the barrier energy for water oxidation. As a result, the CCN@FFC electrode shows multiple functionalities in photoelectrocatalysis: only a low overpotential of 68 mV, 182 mV, and 1.435 V is required to deliver 10 mA cm^-2 current densities for the photoassisted HER, OER, and overall water splitting, respectively. This directional charge transfer modulation strategy may facilitate the design of highly active and cost-effective multifunctional catalysts for energy conversion and storage.