Development of electrolysis systems for ambient temperature CO2 reduction

The electrochemical CO₂ reduction reaction (CO₂RR) at ambient temperature holds great promise as a technology for storing intermittent and fluctuating renewable electricity while producing valuable carbon-containing feedstocks. As such, it has the potential to play a crucial role in closing the carbon cycle. Over the past decade, extensive research has focused on developing catalysts that enhance selectivity and reduce the overpotential of CO₂RR. However, further attention should be directed towards the design of electrolyzers and integrated systems to achieve high current densities, improved energy efficiency, carbon efficiency, and stability. This review categorizes electrolysis systems into H-cells, gas diffusion electrode (GDE)-based flow cells, and membrane electrode assemblies (MEAs). In H-cells, the relatively low solubility of CO₂ in aqueous electrolytes limits current density, and strategies to enhance CO₂ mass transport are discussed. For GDE-based flow cells, strategies to maintain the hydrophobicity of GDEs are examined. Additionally, the impact of pH and alkali cations on energy efficiency, carbon efficiency, and anti-flooding performance is reviewed. MEAs with anion exchange membranes, cation exchange membranes, bipolar membranes, and solid-state electrolytes are introduced, with an exploration of the challenges associated with each type. Furthermore, tandem systems for CO₂COC₂₊ conversion are presented, including single cells incorporating two types of catalysts and cascades of two individual cells for CO₂RR to CO and CO reduction, respectively. Finally, the review outlines future directions for CO₂RR electrolysis systems and highlights the potential contributions of operando technologies and theoretical simulations.