Weakened Interfacial Hydrogen Bond Connectivity Drives Selective Photocatalytic Water Oxidation toward H₂O₂ at...

The formation of H₂O₂ through the two-electron photocatalytic water oxidation reaction (WOR) is significant but encounters the competition with the four-electron O₂ evolution reaction. Recent studies showed a crystal-phase dependence in H₂O₂ selectivity, where high purity brookite TiO₂ (b-TiO₂) exhibits remarkable H₂O₂ selectivity in contrast to the common rutile phase TiO₂ (r-TiO₂). However, the origin of such a structure-induced selectivity preference remains elusive, primarily due to the complexities associated with the solid-liquid interface system and excited-state chemistry. Herein, we conducted a comprehensive investigation into the selectivity mechanism of WOR at the water/b-TiO₂(210) and water/r-TiO₂(110) interfaces, employing first-principles molecular dynamics simulations and microkinetic analyses. Intriguingly, our results reveal that the intrinsic catalytic ability of the b-TiO₂(210) itself does not enhance H₂O₂ selectivity compared to r-TiO₂(110). Instead, it is the weakened interfacial hydrogen bond connectivity, modulated by the herringbone-like local atomic structure of the b-TiO₂(210) surface, that determines the selectivity. Specifically, this weakened H-bond connectivity (i.e., local low water density) at the interface, owing to the strong water adsorption and distinct adsorption orientation, can stabilize the OH^• radical and inhibit its deprotonation, leading to an improved H₂O₂ selectivity. By contrast, the relatively strong interface H-bond connectivity established over r-TiO₂(110) accelerates the deprotonation of OH^•, with the OH^• coverage being 3 orders of magnitude lower than at the water/b-TiO₂(210) interface. This study quantitatively demonstrates that the local H-bond structure (water density) at the liquid/solid interface significantly influences photocatalytic selectivity, and this insight may offer a rational approach to enhance the H₂O₂ selectivity.