Dynamic Oxygen Vacancy Formation via Photoexcitation in Sn-Modified Defective BiOCl Nanoflowers for Enhanced Photocatalytic Nitrogen Fixation

Oxygen vacancies (OVs) play a crucial role in photocatalytic nitrogen fixation, yet current studies predominantly focus on preconstructed OVs (PC-OVs), with limited attention given to photoexcitation-induced OVs (PE-OVs). In this work, Sn-doped BiOCl-VO (Sn-BOC-VO) was synthesized via a facile one-pot hydrothermal method to actively generate PE-OVs. EPR analysis confirmed that Sn doping promotes the formation of PE-OVs. Quasi in situ XPS revealed that light irradiation further enhances OVs generation in Sn-BOC-VO and induces electron transfer from the O and Bi to the Sn. Photoelectrochemical tests demonstrated that Sn-BOC-VO improves visible-light absorption, facilitates charge separation, and suppresses carrier recombination, collectively leading to a 16.8-fold increase in the nitrogen fixation rate compared to BOC-VO. In situ DRIFTS spectroscopy tracked key reaction intermediates, while DFT calculations indicated electron transfer from Sn-BOC-VO to adsorbed N2, highlighting the synergy between Sn and OVs in promoting N2 activation and improving the photocatalytic nitrogen reduction reaction (pNRR) efficiency. Importantly, Sn-BOC-VO exhibits a reduced energy barrier of 1.81 eV for the rate-determining step, which is significantly lower than that of BOC-VO (2.22 eV), underscoring the critical role of Sn in optimizing reaction kinetics. This study offers insights into the design of photoexcited OV-active sites and emphasizes the dynamic role of OVs in catalytic reactions.