Dual-Defective Two-Dimensional/Two-Dimensional Z-Scheme Heterojunctions for CO2 Reduction

The target of photocatalytic CO2 reduction is to achieve high selectivity, efficiency, and stability for a single chemical/fuel production. The construction of conventional Z-scheme heterojunctions is beneficial to improve the interfacial charge separation and redox capacities. However, the random dimensions of junction component(s) undermine the charge-to-surface transport for catalytic reactions, and the limited chemical structures of catalysts restrict surface activity/selectivity tailoring. In this work, we successfully overcome these issues by stacking/constructing an ultrathin dual-defective two-dimensional (2D)/2D Z-scheme heterojunction with growing functional anionic vacancies onto both reductive and oxidative components of the Z-scheme. The O-vacancy-rich BiOCl/N-vacancy-rich g-C3N4-based 2D Z-scheme exhibits excellent photoactivity in CO2 reduction. The rate of CO2 photoreduction to CO is around 45.33 μmol g–1 h–1, which is 11.7- and 12.2-fold those of untreated bulk g-C3N4 and pristine BiOCl, respectively. Among them, N-vacancy-rich g-C3N4 exhibits active and selective photoreduction ability, accompanied with oxidation reactions from O-vacancy-rich BiOCl. Such ultrathin defective Z-schemes not only retain their original features, i.e., enhanced charge separation and redox capacities, but also extend to lower energy photon absorption and ameliorate charge-to-surface transport in two redox components. Besides, density functional theory calculations unveiled the thermodynamically favored CO2-to-CO reduction path and energy barrier's stepwise reduction at the COOH-to-CO rate-limiting step from defective g-C3N4 to the single redox component defective junction and further to the defective junction with both redox components. This work provides an effective adaptable dual-defect engineering on 2D/2D heterojunctions to enhance CO2 photoreduction.