Switching reduction selectivity of diamond electrodes with heavily N-doped surface nanolayers by visible light irradiation

The requirement of lowering CO 2 emissions has become a critical global challenge, and has driven the demand for technologies that enable net negative carbon emissions. Among the various available strategies, the removal of CO 2 via chemical reduction to CO presents a viable option. In particular, the use of hydrated electrons to reduce CO 2 to CO has emerged as a promising and efficient approach. In this study, we investigated the reduction of CO 2 , as induced by visible light, on heavily N-doped diamond electrodes based on detonation nanodiamond (DND). By varying key reaction parameters such as the electrode potential, light intensity, and electrode structure, we unraveled the mechanism that enables the two competing reactions—the reduction of CO 2 to CO vs. the hydrogen evolution reaction (HER)—to be selectively controlled. Our findings reveal that the valence-band electrons primarily drive the HER, whereas the conduction-band electrons (excited by visible light) preferentially power CO 2 reduction. This mechanistic distinction allows the reaction pathway to be selected by irradiation with visible light, and provides a novel strategy for optimizing CO 2 conversion processes. The insights from this study offer valuable guidance for industrial applications, particularly methanol synthesis, where precise control over the hydrogen-to-CO ratio is crucial for process efficiency.