Water Splitting with a Single-Atom Cu/TiO₂ Photocatalyst: Atomistic Origin of High Efficiency and Proposed Enhancement by Spin Selection

Abstract

Anatase TiO 2 is an intensely investigated photocatalytic material due to its abundance and chemical stability. However, it suffers from weak light harvesting and low photocatalytic efficiency. Experiments show that light absorption and photocatalytic properties can be enhanced simultaneously by TiO 2 doping with well-dispersed Cu atoms, forming a single-atom catalyst (Cu/TiO 2 ) that can be used for solar water splitting and other applications. By performing ab initio nonadiabatic molecular dynamics simulations, we demonstrate that Cu/TiO 2 is inactive before light irradiation due to rapid electron–hole recombination via both shallow and deep traps. Surprisingly, the shallow trap is more detrimental to the Cu/TiO 2 performance than the deep trap because it couples better to free carriers. After light irradiation, leading to electron transfer and Cu/TiO 2 protonation, the shallow trap is eliminated, and a local distortion around the Cu atom stabilizes the deep trap state on the Cu d-orbital, decoupling it from free charges and giving rise to high photocatalytic hydrogen generation activity. We further demonstrate that the photocatalytic performance of Cu/TiO 2 can be enhanced by spin selection, achievable experimentally via optical intersite spin transfer or chiral semiconductor coating. Both H adsorption and spin selection enhance charge carrier lifetimes by an order of magnitude. The spin selection mechanism does not require formation of the H species, which necessitates concurrent sources of electrons and protons and which is intrinsically unstable because water splitting involves frequent proton shuffling. Our results rationalize the experimental observations at the atomistic level, provide mechanistic insights into operation of single atom photocatalysis, and demonstrate that spin selection can be used to develop advanced and efficient systems for solar energy conversion.

CO Adsorbate Promotes Polaron Photoactivity on the Reduced Rutile TiO2(110) Surface

“…Our previous simulations using trajectories of similar length showed good results for a broad range of materials, including pristine and doped TiO 2 and TiO 2 sensitized with other semiconductors. 62 , 71 , 96 , 97 …”

Correlated organic–inorganic motion enhances stability and charge carrier lifetime in mixed halide perovskites

“…Therefore, decoherence correction is needed to be taken into account in the NA-MD simulation of nonradiative electronhole recombination. The approach has been widely applied to the study of photoexcitation dynamics for a broad range of systems, including perovskites containing defects [33][34][35] and grain boundaries, [36][37][38] transition metal oxides, 39,40 transition metal dichalcogenide heterostructures, 41,42 etc.…”

Single-atom catalysts for high-efficiency photocatalytic and photoelectrochemical water splitting: distinctive roles, unique fabrication methods and specific design strategies

“…82–85 Among them, tuning the electronic structure of the substrate and reducing the particle size of cocatalysts are particularly effective in boosting the photocatalytic activity due to some additional benefits brought about by these two strategies including simultaneously enhanced light-harvesting and charge transfer capability. 57,86,87…”