Insights into the Role of Electrolyte Ionophore on Electrochemical Reduction of CO2

Abstract

Electrochemical reduction of carbon dioxide (CO2) to value-added chemicals and fuels offers a sustainable route to utilize CO2 by exploiting renewable energy source. The electrolyte plays a significant role by taking advantage of the interaction between electrocatalytic surface and electrolyte. In this work, we present a CO2 conversion flow cell with an external compartment for a reference electrode (AgCl/Ag) to investigate the effect of alkaline electrolyte composition on the direct conversion of CO2 to fuels and commodity chemicals under ambient conditions. In this flow cell, a catalytic Ag-based gas diffusion electrode (GDE) was employed for CO2 reduction reaction, while an anode electrode was prepared with a RuO2 catalytic GDE. The gaseous products generated from the cell were analyzed with a Gas Chromatography (GC), while the liquid products were analyzed with Nuclear Magnetic Resonance Spectroscopy (NMR). Electrolytes with various cations (Li+, Na+, K+) and anions (OH-, HCO3 -, CO3 2-) were investigated. With a KOH electrolyte (combination of the cation K+ and anion OH-), high faradaic efficiency (~ 97%) was achieved at -1.115 V vs SHE toward the formation of syngas (CO + H2) and ~ 60% faradaic efficiency was obtained toward the product of ethanol. The overall energy conversion efficiency could be up to ~ 45%. In consideration of faradaic efficiency, energy conversion efficiency, and the production of CO and ethanol, the preferable option of anions followed the order of OH- > HCO3 - > CO3 2-, while the option for cations was in the order of K+ > Na+ > Li+.