Synergistic effects in NiMnEr-LDH: d-d-f orbital overlap enables efficient CO₂ photoreduction

To achieve high selectivity in photocatalytic CO₂ reduction (CO₂PR), developing ternary layered double hydroxide (LDH) photocatalysts through a simple method is essential. Herein, Er introduction modulates the orbital energies of metal constituents, enhancing unsaturated active sites and forming highly active NiMnEr-LDH. This promotes photogenerated carrier separation and improves reducibility. Under visible light (λ > 400 nm), NiMnEr-LDH achieves a CO production rate of 1403.72 μmol g^-1 h^-1-about 12.4 times that of pristine NiMn-LDH-with 96.87% CO selectivity. Structural and photoelectrochemical analyses reveal that Er incorporation not only preserves the defect-rich monolayer configuration but also promotes the formation of Ni²⁺ and Mn³⁺, creating synergistic metal active sites. The in situ DRIFTS and theoretical calculations demonstrated that Er induces d-d-f orbital overlap among the metals, lowering the energy barrier of the *COOH formation step (0.33 eV) and enabling highly active and selective CO generation. This work provides new insights into efficient photocatalytic CO₂ reduction by modulating the orbital structure of LDH layers using rare-earth elements with f-orbitals.