Synergistic Engineering of Zinc Vacancies and Er-Doping in ZnIn2S4 Nanosheets for Enhanced CO2 Photoreduction via Optimized Charge Dynamics

Although extensive research has been conducted on cation vacancies in photocatalysts, the significance of vacancy defects in photocatalytic reactions and deep-going understanding of the intrinsic mechanisms are still limited. Herein, an appropriate introduction of zinc vacancies on ZnIn₂S₄ (ZIS) is rationally designed through Er or La (Er/La)-doping. Aberration-corrected scanning transmission electron microscopy (STEM) directly demonstrates distinct zinc vacancies (V_Zn), which is also confirmed by electron spin resonance analysis. The results of experiments and density functional theory (DFT) calculations manifest that Er/La-doping not only promotes the formation of V_Zn but also enhances the built-in electric field, thus facilitating the rapid transfer of carriers. In addition, femtosecond transient absorption spectroscopy (fs-TAS) reveals that V_Zn induces a supplementary charge transfer pathway, thereby enhancing charge separation efficiency. As a result, the desired photocatalytic CO₂ reduction reaction (CO₂RR) to syngas capacity is finally achieved on Er_0.2-ZIS, with tunable H₂/CO ratios, exceeding that of untreated ZIS by over 2 times. This study not only exploits a novel avenue to develop high-activity cation vacancies photocatalysts but also provides new perspectives in regulating the photogenerated carrier dynamics.