Probing the role of surface hydroxyls for Bi, Sn and In catalysts during CO2 Reduction

• Surface of electrodeposited Bi, Sn and In catalysts are Bi 0 , SnO and In 2 O 3 during CO 2 RR. • The affinity of hydroxyls on active sites follows the trend of Bi 0 < SnO < In 2 O 3 . • CO 2 RR on Bi, Sn and In has two pathways, one involves interaction of CO 2 with *OH, the other proceeds on *OH-free surface. Electrodeposited Bi, Sn and In catalysts are employed as model catalysts to investigate the nature of active sites and the influence of surface hydroxyls on the formation of formate during CO 2 electroreduction (CO 2 RR). With SEM, XPS, in situ XRD, electrochemical measurements and DFT calculations, the active sites are Bi 0 , SnO and In 2 O 3 , with their affinities to hydroxyls following the trend of Bi 0 < SnO < In 2 O 3 . KIE analysis and in situ ATR-IR suggest two parallel pathways for formate production, with one proceeding on hydroxylated sites involving the interaction of CO 2 with hydroxyls to form bicarbonates and another one proceeding on hydroxyl-free sites involving *OCHO as the key intermediate. The participation of hydroxyl groups in CO 2 RR follows Bi < Sn < In depending on their affinity to hydroxyls.