Alkaline CO2 Electrolysis toward Selective and Continuous HCOO– Production over SnO2 Nanocatalysts

Electrolyte pH is an important parameter in determining the equilibrium concentrations of the carbon dioxide–bicarbonate–carbonate system as well as in mapping out the thermodynamically stable phases of tin dioxide (SnO2) in an aqueous electrochemical system. Thus, we explored an optimized region in the combined potential–pH (E–pH) diagram of the two systems where there is a simultaneously high catalytic activity for carbon dioxide (CO2) electrolysis and good phase stability for the SnO2 nanocatalysts. Our results suggest that choosing the right E–pH combination, which in this case is at −0.6 V (vs RHE) and pH 10.2, results in a high faradaic efficiency of 67.6% for formate (HCOO–) synthesis and an efficiency retention of ∼90% after 5 h while maintaining the stability of the oxide structure and avoiding the formation of carbon monoxide. Widely applicable to neutral or near-neutral pH metal oxide electrocatalysts, optimized alkaline CO2 electrolysis offers distinct advantages in terms of the three major catalyst properties: activity, selectivity, and stability.