Superior CO ₂ Conversion Performance by Er‐Doped BiOCl Nanosheets Through Synergistic Photocatalytic Memory Effect and Er‐Doping

To search for efficient carbon dioxide reduction photocatalysts, rare‐earth element doping has attracted considerable attention owing to their unique electronic structures and energy levels, which significantly enhance light absorption and charge‐transfer efficiency. In this work, Er‐doped two‐dimensional ultrathin BiOCl nanosheets are synthesized via a surfactant‐assisted hydrothermal method. Er‐doping not only suppresses the photogenerated charge carrier recombination but also further enhances the photocatalytic memory effect of BiOCl nanosheets. The synergistic effect of Er doping and the photocatalytic memory effect induced by prior visible‐light irradiation largely modulates the internal electronic state of BiOCl nanosheets. Experimental and density functional theory analysis results demonstrate that desirable changes subsequently occur in Er‐doped BiOCl nanosheets, compared with pure BiOCl nanosheets, including the generation of abundant oxygen vacancies, improvement of visible light absorption, higher photogenerated electron reduction potential, stronger piezoelectric response, better charge carrier separation and transfer, enhanced CO 2 adsorption, and lower CO 2 activation energy. Bi 0.98 E 0.02 OCl nanosheets (2 mol% Er) exhibit superior CO 2 ‐to‐CO reduction performance in photocatalysis, piezocatalysis, and photopiezocatalysis without co‐catalysts, photosensitizers, or sacrificial agents. With nearly 100% selectivity, the photopiezocatalytic CO 2 ‐to‐CO rate reaches ~3921.2 μmol g −1 h −1 under visible light and ultrasonication, far exceeding previous reports.