Isolated-atom Engineering for Active Sites Design Promotes Solar-driven Carbon Dioxide Conversion

Abstract

Solar-driven carbon dioxide (CO2) reduction to value-added chemicals and fuels offers a promising route toward carbon neutrality and sustainable energy development. However, the complexity of the photocatalytic CO2 reduction reaction (CO2RR) including the activation of the chemically inert C=O bond (~750 kJ/mol) of CO2, diverse intermediate pathways, energy-intensive C-C coupling and microenvironment optimization, poses significant challenges to achieving high efficiency and selectivity. To address these limitations, isolated-atom engineering has emerged as an effective strategy for active site design, enabling the simultaneous optimization of multiple limiting factors in CO2RR. Under this concept, three research projects were conducted focusing on the rational design of isolated-atom active sites to improve both activity and product selectivity. In the first project, bismuth (Bi) single atoms were employed as active sites, achieving selective photocatalytic production of formic acid as well as cyclic carbonates via CO2 cycloaddition. The formic acid production pathway underwent a thermodynamically favorable *HCOO intermediate upon the Bi isolated atom engineering. However, the selective regulation for *HCOO intermediates limited its capacity to convert CO2 into C2+ products. The second project targeted C2+ chemical production using ruthenium (Ru) single atoms. The strong *CO adsorption on Ru sites allowed for C-C coupling process by thermodynamically favorable *CO-*CHO dimerization pathway, resulting in high ethanol productivity and selectivity (over 90%). In situ analysis revealed a dynamic reconstruction scheme between Ru0-O and Ruδ+-O species during the photocatalytic CO2RR to ethanol. However, the potential competitive reaction (HER) should be further optimized, aiming to improve the electrons contribution to CO2RR. In the third project, Ru-Pd dual-atom sites were designed to optimize the CO2RR reaction environment and suppress the competing hydrogen evolution reaction (HER). The dual-atom configuration enabled synergistic interactions, enhancing electron transfer toward CO2RR upon Ru sites while suppressing HER by proton spillover upon Pd sites, respectively. Together, these studies offer valuable insights into the dynamical reconstruction behavior of isolated-atom active sites during photocatalytic CO2RR and highlight their potential in overcoming critical limitations in photocatalytic CO2 reduction field.