Acidic CO2 electrolysis addressing the "alkalinity issue" and achieving high CO2 utilization.

Abstract

Electrochemical CO2 reduction reaction (CO2RR) provides a promising approach for sustainable chemical fuel production of carbon neutrality. Neutral and alkaline electrolytes are predominantly employed in the current electrolysis system, but with striking drawbacks of (bi)carbonate (CO32-/HCO3-) formation and crossover due to the rapid and thermodynamically favorable reaction between hydroxide (OH-) with CO2, resulting in low carbon utilization efficiency and short-lived catalysis. Very recently, CO2RR in acidic media can effectively address the (bi)carbonate issue; however, the competing hydrogen evolution reaction (HER) is more kinetically favorable in acidic electrolytes, which dramatically reduces CO2 conversion efficiency. Thus, it is a big challenge to effectively suppress HER and accelerate acidic CO2RR. In this review, we begin by summarizing the recent progress of acidic CO2 electrolysis, discussing the key factors limiting the application of acidic electrolytes. We then systematically discuss addressing strategies for acidic CO2 electrolysis, including electrolyte microenvironment modulation, alkali cations adjusting, surface/interface functionalization, nanoconfinement structural design, and novel electrolyzer exploitation. Finally, the new challenges and perspectives of acidic CO2 electrolysis are suggested. We believe this timely review can arouse researchers' attention to CO2 crossover, inspire new insights to solve the "alkalinity problem" and enable CO2RR as a more sustainable technology.