Electrocatalytic CO2 reduction promoted by catalyst-bound proton-abstracting ligands

The electrochemical CO 2 reduction reaction (eCO 2 RR), which is well suited for reducing atmospheric CO 2 levels and generating clean energy. Water is the main proton source in the electrochemical reduction process. However, water features a high dissociation energy barrier, and most protons are involved in HER, so that only a small amount of H + is used in the CO 2 reduction reaction. Herein, we reveal that appropriately chosen ligands on the catalyst surface can abstract protons from water, store them, and transfer them to CO 2 to promote the formation of COOH and improve the proton utilization efficiency of the eCO 2 RR. Moreover, the activity of the ligand complexed protons is shown to be lower than that of free ones and thus result in HER inhibition our ligands with different pK a values (i.e., proton release capacities) are used to functionalize ZnO, and the plot of pK a vs. the FE CO exhibits a volcano shape. Overly small pK a leads to the combination of abundant protons with each other and the dominance of the HER, whereas overly large pK a does not promote the utilization of H + by CO 2 . Ligands with suitable pK a can properly bind and release protons, which is conducive to the formation of *COOH, thus accelerating eCO 2 RR. In particular, mercaptobenzoic acid (MBA) considerably enhances catalytic activity because of its moderate pK a (FE CO  = 90 %, which is 2 times higher than the FE CO of unmodified ZnO, and j CO is nearly 5 times higher). In situ infrared spectroscopic analysis proves that the above ligand can abstract protons from H 2 O and then release them, promoting the dissociation of H 2 O. Theoretical calculations show that pK a affects the ability of ligands to abstract and release protons.