Strengthening built-in electric field and enriching active sites on cobalt-doped ZnSn(OH)6/ZnWO4 heterojunction to promote photocatalytic reduction of CO2

The photocatalytic activity of photocatalysts is often limited by rapid recombination of photo-induced electron-hole pairs, insufficient active sites and slow reaction kinetics. In this study, the Co-doped ZnSn(OH)₆/ZnWO₄ heterojunctions with oxygen vacancies and Lewis basic sites were synthesized for efficient photocatalytic CO₂ reduction. The Co-doped ZnSn(OH)₆/ZnWO₄ exhibited superior photoelectrochemical properties to the ZnSn(OH)₆ and ZnWO₄. Results of kelvin probe force microscopy (KPFM) and electron density difference calculations demonstrated that Co doping induced lattice distortion in ZnSn(OH)₆, generating a local electric field, which, in synergy with oxygen vacancies in ZnWO₄, further enhanced the built-in electric field (IEF) within the Co-doped ZnSn(OH)₆/ZnWO₄ heterojunction, significantly accelerating carriers separation. Density functional theory (DFT) calculation also revealed that the Lewis basicity of ZnSn(OH)₆ and oxygen vacancies in ZnWO₄ enhanced CO₂ adsorption on the Co-doped ZnSn(OH)₆/ZnWO₄ heterojunction, facilitating CO₂ conversion. The Co-ZnSn(OH)₆/ZnWO₄-V_O composite exhibited the highest CO production rate (90.18 μmol·g⁻¹·h⁻¹) during CO₂ reduction, which was 25.47 and 1.28 times of those of ZnSn(OH)₆ and Co-ZnSn(OH)₆/ZnWO₄, respectively. The main reaction intermediates were identified and CO₂ reduction mechanism was proposed. This work provides reference to improve photocatalytic activity by enhancing IEF and increasing active sites in heterojunctions.