Chirality induced spin selectivity suppresses competing hydrogen evolution during electrochemical CO2 reduction

In this paper, we prepare chiral, helical-structured copper (Cu) electrodes that manifest product selectivity control during the CO2 reduction reaction (CO2RR) owing to CISS and elucidate the mechanism using (spectro)electrochemistry and ultrafast spectroscopy. Regardless of their handedness, the chiral Cu electrodes exhibit a lower onset potential for CO2RR compared to their achiral counterpart by suppressing the hydrogen evolution reaction. The Faradaic efficiency of H2 production at the chiral electrodes is significantly lower than that at the achiral electrodes, whereas formate is only produced on the chiral electrodes. Time-resolved Kerr ellipticity indicates that carriers traveling through the helical structure become spin polarized, inducing an electron spin accumulation at the electrode surface, which provides the evidence that the topological structure of the electrocatalyst causes the spin polarization. This spin polarization reduces hydrogen formation due to the Pauli exclusion principle for two-electron bond formation and thereby promotes CO2 reduction to CO and formate. Our findings provide insights into the potential of chiral catalysts for controlling selectivity during CO2RR as well as other valuable reduction reactions involving nitrogen or CO where hydrogen evolution also is an undesired side reaction.