Addressing the Carbonate Issue: Electrocatalysts for Acidic CO₂ Reduction Reaction

Electrochemical CO₂ reduction reaction (CO₂RR) powered by renewable energy provides a promising route to CO₂ conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO₂ to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO₂RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO₂RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO₂RR. Subsequently, an in-depth analysis of recent advancements in acidic CO₂RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO₂RR systems. Finally, the existing challenges and future directions in the design of acidic CO₂RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.