Identification of intrinsic vacancies and polarization effect on ternary halo‐sulfur‐bismuth compounds for efficient CO2 photoreduction under near‐infrared light irradiation

Abstract Ternary halo‐sulfur bismuth compound Bi 19 X 3 S 27 (X = Cl, Br, I) with distinct electronic structure and full‐spectrum light‐harvesting properties show great application potential in the CO 2 photoreduction field. However, the relationship between photocatalytic CO 2 reduction performance and the function of halogens in Bi 19 X 3 S 27 is still poorly understood. Herein, a series of Bi 19 X 3 S 27 nanorod photocatalysts with intrinsic X and S dual vacancies were developed, which showed significant near‐infrared (NIR) light responses. The types and concentrations of intrinsic vacancies were confirmed and quantified by positron annihilation spectrometry and electron spin resonance spectroscopy. Experimental results showed that Br atoms and intrinsic vacancies (dual Br‐S) in Bi 19 Br 3 S 27 could greatly enhance the internal polarized electric field and improve the transfer and separation of photogenerated carriers compared with Bi 19 Cl 3 S 27 and Bi 19 I 3 S 27 . Theoretical calculations revealed that Br atoms in Bi 19 Br 3 S 27 could facilitate CO 2 adsorption and activation and decrease the formation energy of reactive hydrogen. Among Bi 19 X 3 S 27 nanorods, Bi 19 Br 3 S 27 nanorods revealed the highest CO 2 photoreduction activity with CO yield rate of 28.68 and 2.28 μmol g catalyst −1 h −1 with full‐spectrum and NIR lights, respectively. This work presents an atomic understanding of the intrinsic vacancies and halogen‐mediated CO 2 photoreduction mechanism.