CO2 electrolysis: Advances and challenges in electrocatalyst engineering and reactor design

Electrochemical reduction of CO₂ (CO₂RR) coupled with renewable electrical energy is an attractive way of upgrading CO₂ to value-added chemicals and closing the carbon cycle. However, CO₂RR electrocatalysts still suffer from high overpotential, and the complex reaction pathways of CO₂RR often lead to mixed products. Early research focuses on tuning the binding of reaction intermediates on electrocatalysts, and recent efforts have revealed that the design of electrolysis reactors is equally important for efficient and selective CO₂RR. In this review, we present an overview of recent advances and challenges toward achieving high activity and high selectivity in CO₂RR at ambient conditions, with a particular focus on the progress of CO₂RR electrocatalyst engineering and reactor design. Our discussion begins with three types of electrocatalysts for CO₂RR (noble metal-based, none-noble metal-based, and metal-free electrocatalysts), and then we examine systems-level strategies toward engineering specific components of the electrolyzer, including gas diffusion electrodes, electrolytes, and polymer electrolyte membranes. We close with future perspectives on catalyst development, in-situ/operando characterization, and electrolyzer performance evaluation in CO₂RR studies.