Modulation of Photocatalytic CO Reduction by - Codoping Engineering of Single-Atom Catalysts.

Transition metal (TM) single-atom catalysts (SACs) have been widely applied in photocatalytic CO reduction. In this work, - codoping engineering is introduced to account for the modulation of photocatalytic CO reduction on a two-dimensional (2D) bismuth-oxyhalide-based cathode by using first-principles calculation. - codoping is established via the Coulomb interactions between the negatively charged TM SACs and the positively charged vacancy () in the dopant-defect pairs. Based on the formation energy of charged defects, neutral dopant-defect pairs for the Fe, Co, and Ni SACs () and the -1 charge state of the Cu SAC-based pair () are stable. The electrostatic attraction of the - codoping strengthens the stability and solubility of TM SACs by neutralizing the oppositely charged defect and TM dopant. The - codoping stabilizes the electron accumulation around the TM SACs. Accumulated electrons modify the -orbital alignment and shift the -band center toward the Fermi level, enhancing the reducing capacity of TM SACs based on the d-band theory. Besides the electrostatic attraction of the - codoping, the also accumulates additional electrons surrounding Cu SACs and forms a half-occupied state, which further upshifts the -band center and improves photocatalytic CO reduction. The metastability of multivacancies limits the concentration of the - pairs with multivacancies ( (n > 1)). Positively charged centers around the (n > 1) hinders the CO reduction by shielding the charge transfer to the CO molecule.