Evidence of direct charge transfer in plasmon-mediated photocatalytic water splitting: A time-dependent density functional theory study

Photocatalytic water splitting is a promising route for hydrogen production and solar energy storage. Plasmon-mediated water splitting has the potential to harvest photons with longer wavelengths compared with semiconductor-based photocatalysis. However, the mechanism of plasmon-induced charge transfer, the determining step of photochemistry, is not well understood. Here, we studied plasmon-mediated water splitting at atomic length scale and femtosecond timescale. Linear-response time-dependent density functional theory calculations and Ehrenfest dynamics simulations were performed for a realistic H2O@Au6 model excited by the femtosecond laser. Wavelength-dependent charge transfer mechanisms were demonstrated. Especially, for the excitation of 2.25 eV that falls into the visible spectrum, evidence was presented for the dominant direct transfer of d-orbital electrons from the gold cluster to the adsorbed water molecule. In this mechanism, the charge transfer leapfrogs the processes of excitation and thermalization within gold described in the classical theory. The results can assist the design of more energy-efficient solar water splitting.