Reaction Mechanism of Photocatalytic Hydrogen Production at Water/Tin Halide Perovskite Interfaces

While instability in aqueous environment has longimpeded employment of metal halide perovskites for heterogeneousphotocatalysis, recent reports have shown that some particular tin halideperovskites (THPs) can be water-stableandactive in photocatalytichydrogen production. To unravel the mechanistic details underlying thephotocatalytic activity of THPs, we compare the reactivity of the water-stable and active DMASnBr3(DMA = dimethylammonium) perovskiteagainst prototypical MASnI3and MASnBr3compounds (MA =methylammonium), employing advanced electronic-structure calcula-tions. Wefind that the binding energy of electron polarons at the surfaceof THPs, driven by the conduction band energetics, is cardinal forphotocatalytic hydrogen reduction. In this framework, the interplaybetween the A-site cation and halogen is found to play a key role indefining the photoreactivity of the material by tuning the perovskiteelectronic energy levels. Our study, by elucidating the key steps of the reaction, may assist in development of more stable andefficient materials for photocatalytic hydrogen reduction