Inhibition of hydrogen evolution without debilitating electrochemical CO2 reduction via the local suppression of proton concentration and blocking of step-edges by pyridine functionalization on Cu electrocatalysts

Abstract

Electrochemical carbon dioxide reduction reaction (CO₂RR) into chemicals can store renewable electricity and simultaneously control global warming. Albeit inexpensive copper electro-catalyzes CO₂ to hydrocarbons at reasonable rates, it suffers from low selectivity due to high hydrogen evolution reaction (HER) activity. Although an increase in bulk pH suppresses HER activity, this leads to a CO₂ reaction with hydroxide and the formation of bicarbonate and carbonate ions. In contrast, we demonstrate selective HER suppression by functionalizing Cu electrocatalysts with pyridine molecules without a commensurate reduction in CO₂RR activity. Density functional theory (DFT) based computational results suggest that the decrement in the H binding energy and blockage of step edge atoms (which are the most active sites for the HER) by pyridine molecules are the reasons for selective suppression of the HER activity on the copper surface after pyridine functionalization. Further, an insignificant decrease in CO binding is the reason behind the lack of suppression of the CO₂RR activity. This study provides pointers towards better electrocatalyst design for the CO₂RR.