Switching from two-electron to four-electron photocatalytic pure water splitting via band bending engineering with boosted activity

Photocatalytic pure water splitting using particulate photocatalyst is usually restricted by the extremely slow reaction kinetics. Herein, we demonstrated a novel Z-scheme heterojunction, composed of a phosphatized p-type gallium indium zinc oxynitride (GIZON-P) and a n-type g-C₃N₄ (CN). Results show that phosphorization could reduce hole concentration within p-type GIZON, resulting in the transition of Z-scheme band structure into type-Ⅱ style. This transformation leads to a completely changed reaction mechanism, i.e., from a two-electron H₂/H₂O₂ production to a four-electron H₂/O₂ generation. Although this four-electron pathway is dynamically unfavorable, the rapid charge separation by the type-II band arrangement together with thin InP layer at the surface of GIZON-P could remarkably accelerate the rate-limited O₂-evolution process. The phosphatized composite presents an excellent photocatalytic performance, with a H₂/O₂ rate of 1340/643 μmol h g. The gained quantum yield of 12.6% at 430 nm is among the best results in photocatalytic pure water splitting.