Visualizing the dynamic evolution of light-sensitive Cu/Cu sites during photocatalytic CO reduction with an advanced in situ EPR spectroscopy.

Elucidation of the dynamic evolution of active sites is still a challenge in investigating the catalytic mechanism mainly due to the difficulty in accurately detecting the transient structural changes of active sites under operating conditions. Here, we develop an advanced in situ electron paramagnetic resonance (EPR) spectroscopy, which could sensitively monitor and visualize the dynamic evolution of paramagnetic active sites during photoreduction CO. In situ results reveal that the photoactivated Cu sites from CuO nanoclusters/TiO serve as the authentic active sites in the reaction and exhibit self-regenerative capability. The CO molecules can acquire electrons and get activated by the photoactivated Cu, leading to the transition of Cu sites into Cu sites. Subsequently, the Cu sites expedite the generation of hydrogen protons through antiferromagnetic coupling with hydroxyl radicals, thereby promoting the production of the final product CH via a multi proton-coupled electron transfer (PCET) process. This work reveals and visualizes the dynamic evolution of Cu-based active sites during photocatalytic reactions by combined in situ characterizations, providing new perspectives on the mechanistic understanding of paramagnetic active sites under operation.