Optimized Ternary PdCuFe Prussian Blue Analogues for Selective Photocatalytic Conversion of CO2 to CO

Abstract Photocatalytic CO2 reduction is hindered by the rigid coordination environments of conventional catalysts, which limit coordinatively unsaturated sites (CUSs), suppress charge transfer, and reduce CO2 binding affinity. Prussian blue analogues (PBAs) offer porous structures and stability, but traditional bimetallic PBAs retain these drawbacks. We introduce Pd2+ into a Cu−Fe cyanide PBA lattice, forming a ternary PdCuFe PBA with high-density CUSs. In this design, Pd sites stabilize *COOH intermediates, Cu sites function as electron reservoirs, and the Fe−CN framework ensures structural integrity. Under visible light without sacrificial agents, the PdCuFe PBA exhibits enhanced CO2 reduction performance, outperforming CuFe and FeFe PBAs by factors of 1.77 and 4.10, respectively. In situ DRIFTS and DFT calculations reveal that Pd incorporation extends light absorption and lowers the *COOH formation energy barrier. This work presents a strategy for designing multimetallic photocatalysts rich in unsaturated active sites for sustainable solar fuel production.