Integration of Co Single Atoms and Ni Clusters on Defect-Rich ZrO₂ for Strong Photothermal Coupling Boosts Photocatalytic CO₂ Reduction

We report a solvothermal method for the synthesis of an oxygen vacancy-enriched ZrO₂ photocatalyst with Co single atoms and Ni clusters immobilized on the surface. This catalyst presents superior performance for the reduction of CO₂ in H₂O vapor, with a CO yield reaching 663.84 μmol g^-1 h^-1 and a selectivity of 99.52%. The total solar-to-chemical energy conversion efficiency is up to 0.372‰, which is among the highest reported values. The success, on one hand, depends on the Co single atoms and Ni clusters for both extended spectrum absorption and serving as dual-active centers for CO₂ reduction and H₂O dissociation, respectively; on the other hand, this is attributed to the enhanced photoelectric and thermal effect induced by concentrated solar irradiation. We demonstrate that an intermediate impurity state is formed by the hybridization of the d-orbital of single-atom Co with the molecular orbital of H₂O, enabling visible-light-driven excitation over the catalyst. In addition, Ni clusters play a crucial role in altering the adsorption configuration of CO₂, with the localized surface plasmon resonance effect enhancing the activation and dissociation of CO₂ induced by visible-near-infrared light. This study provides valuable insights into the synergistic effect of the dual cocatalyst toward both efficient photothermal coupling and surface redox reactions for solar CO₂ reduction.