Effect of Trivalent Metal Cations in Layered Double Perovskites on Highly Selective CO₂ Photoreduction to CO

Trivalent metal cation engineering in vacancy-ordered layered double perovskites (LDP) is a useful strategy to tune photocatalytic activity. However, the regulatory mechanism of cation composition on photocatalytic performance still lacks in-depth understanding. This study explores vacancy-ordered LDP with the formula Cs₄CdX₂Cl₁₂ (X = Bi, Sb) for photocatalytic CO₂ reduction. The catalytic performance is fine-tuned by regulating the composition of M^(III)-site metal ions. The yields of CO and CH₄ from Cs₄CdSb₂Cl₁₂ MCs were measured at 23.81 and 2.68 μmol g^-1, resulting in a CO selectivity of 89.9%. Cs₄CdBi₂Cl₁₂ demonstrated higher yields, with CO and CH₄ produced at 90.77 and 2.53 μmol g^-1, achieving a CO selectivity of 97.2%. In addition, <i>in situ</i> diffuse reflectance infrared Fourier transform spectra reveal that the modulation of metal ions at the M^(III)-position can enhance the photocatalytic activity of Cs₄CdX₂Cl₁₂ (X = Bi, Sb) MCs. Density functional theory (DFT) analysis suggests that Bi displays a lower energy barrier than Sb for the rate-determining step, thus facilitating the effective photocatalytic reduction of CO₂ to CO. These findings highlight the influence of metal cation selection on structural properties and catalytic performance.