Constructing a Z-Scheme Heterojunction Photocatalyst of GaPO4/α-MoC/Ga2O3 without Mingling Type-II Heterojunction for CO2 Reduction to CO.

Constructing Z-scheme heterojunction photocatalysts is a prevalent strategy to prolong the lifetime of photoinduced charge carriers without reducing their redox potentials. Nevertheless, these photocatalysts were usually mingled with type-II heterojunction, leading to a decrease in the redox potentials of photoinduced charge carriers. Herein, based on the absolute electronegativity of semiconductors, a Z-scheme heterojunction photocatalyst of GaPO4/α-MoC/Ga2O3 was designed and successfully constructed, in which the formation of type-II heterojunction was prevented between GaPO4 and Ga2O3. In the GaPO4/α-MoC/Ga2O3 photocatalyst, the conduction band (CB) and valance band (VB) potentials and the Fermi level of Ga2O3 are higher than those of GaPO4, respectively. Under irradiation, photoinduced electrons on the CB of GaPO4 migrate to the electron mediator α-MoC and subsequently recombine with the photoinduced holes of Ga2O3, thereby retaining the photoinduced charge carriers with higher redox potentials. As a result, GaPO4/α-MoC/Ga2O3 exhibits a 4-fold enhancement of activity for CO2 photoreduction, compared to Ga2O3. Photocatalytic mechanism studies indicate that superoxide radicals might be an important intermediate for CO2 reduction to CO. The present work supplies a paradigm to construct a Z-scheme heterostructure without mingling type-II heterojunction via energy band engineering.