Surface hydrogen bond network spatially confined BiOCl oxygen vacancy for photocatalysis

Rational engineering of oxygen vacancy (V_O) at atomic precision is the key to comprehensively understanding the oxygen chemistry of oxide materials for catalytic oxidations. Here, we demonstrate that V_O can be spatially confined on the surface through a sophisticated surface hydrogen bond (HB) network. The HB network is constructed between a hydroxyl-rich BiOCl surface and polyprotic phosphoric acid, which remarkably decreases the formation energy of surface V_O by selectively weakening the metal-oxygen bonds in a short range. Thus, surface-confined V_O enables us to unambiguously distinguish the intrafacial and suprafacial oxygen species associated with NO oxidation in two classical catalytic systems. Unlike randomly distributed bulk V_O that benefits the thermocatalytic NO oxidation and lattice O diffusion by the dominant intrafacial mechanism, surface V_O is demonstrated to favor the photocatalytic NO oxidation through a suprafacial scheme by energetically activating surface O₂, which should be attributed to the spatial confinement nature of surface V_O.