Role of Oxide-Derived\nCu on the Initial Elementary\nReaction Intermediate During Catalytic CO<sub>2</sub> Reduction

The catalytic role of oxide-derived Cu (OD-Cu) in promoting\nCO<sub>2</sub> reduction (CO<sub>2</sub>R) to C<sub>2+</sub> products\nhas\nbeen appreciated for decades. However, the dynamic evolution of the\nsurface oxidation states, together with their real correlation to\nthe binding of reaction intermediates, remains unclear due to technical\nchallenges. Here, we show the time-resolved spectroscopic signatures\nof key OD-Cu-CO<sub>2</sub><sup>•–</sup> intermediates\nduring catalytic CO<sub>2</sub> reduction through one electron transfer\nfrom nanoseconds to seconds time scale. We generated the initial intermediate\nCO<sub>2</sub><sup>•–</sup> radicals in the bulk solution\nand monitored the interfacial reaction kinetics with well-defined\nOD-Cu (Cu(0), Cu(I), and Cu(II)) nanoparticles. Combined with molecular\nsimulations, transient absorption profiles analysis reveals that Cu(I)\ninduced a faster CO<sub>2</sub><sup>•–</sup> radical\ncoupling reaction than Cu(0), whereas Cu(II) is only reduced to Cu(I)\nby the CO<sub>2</sub><sup>•–</sup> radical. Furthermore,\nthe newly developed multistep cumulative pulse methodology uncovered\nthe transition in chemical states of mixed OD-Cu during radical coupling\nreactions. This pulse radiolysis study provides compelling evidence\nfor the beneficial role of subsurface oxides in early time catalytic\nCO<sub>2</sub> transformation.