Perovskite Cs₃Bi₂I₉ Hexagonal Prisms with Ordered Geometry for Enhanced Photocatalytic Hydrogen Evolution

The synthesis of metal halide perovskite/perovskitoid (MHP) photocatalysts with well-defined morphologies and facet-specific redox activity is technically challenging. Herein, using surfactants to control the arrangement of 0D facet-shared [Bi2I9]3– dioctahedra building blocks, we successfully fabricated ordered perovskite Cs3Bi2I9 hexagonal prisms (CBI-HPs). Using Co2+ oxidation and Pt4+ reduction as redox probes, photoexcited holes were shown to spatially migrate to the edge (100) facets while photoexcited electrons migrated to the (006) basal facets, respectively. Density functional theory revealed that the built-in potential of the facet junction between (100) and (006) facets was ∼130 meV. Because of the well-separated redox facets, the photocatalytic hydrogen evolution rate of ordered CBI-HPs via hydroiodic acid splitting reached 1504.5 μmol/h/g, which is 22.1 times that of a disordered CBI photocatalyst. This work guides the rational design of high-performance MHP photocatalysts for solar energy conversion and other applications.