Double-layer effect on the kinetics of CO2 electroreduction at cathodes bearing Ag, Cu, and Ag/Cu nano-arrays electrodeposited by potentiostatic double-pulse

Abstract

Abstract In-doped SnO2 (ITO) cathodes bearing Ag, Cu and bimetallic Ag/Cu nanoparticulate arrays (cathode systems ITO//Ag, ITO//Cu and ITO//Ag/Cu, respectively) were prepared by a potentiostatic double-pulse technique and employed for studying the multi-step charge-transfer kinetics of CO2 electrochemical reduction (CO2ER) in propylene carbonate solution. Our results demonstrated, on one hand, that the current exchange density of the rate-determining step (rds) for the CO2 electrochemical reduction (io,rds) depends, predominantly, on the values achieved by the outer-Helmholtz plane (OHP) potential (ΔψOHP,rds) on the three cathode systems here explored. Furthermore, these results showed that a large ΔψOHP,rds (−647 mV) promoted a large io,rds (1.09 × 10−2 A⋅ cm−2) for CO2 reduction at the cathode system ITO//Cu, whereas a small ΔψOHP,rds (−168 mV) produced a small io,rds (2.05 × 10−4 A⋅ cm−2) for CO2 reduction at the cathode system ITO//Ag. In contrast, intermediate values of ΔψOHP,rds and io,rds (−333 mV, 1.09 × 10−3 A⋅ cm−2) were found for CO2 reduction on the cathode system ITO//Ag/Cu, demonstrating that the individual electrocatalytic properties of Ag and Cu can be coupled in a bimetallic array to intentionally tune the CO2ER rate in nonaqueous solvents having low proton availability.