posted on 2024-02-22, 17:11authored byGuanhua Ren, Min Zhou, Haifeng Wang
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.