Carbon dioxide electrolysis systems for high carbon efficiency

• CO 2 electrolysis requires energy- and carbon-efficient systems. • Present-day tandem CO 2 electrolysis enables the lowest energy intensity. • Efficient CO production technologies are key for tandem CO 2 electrolysis. • Acidic CO 2 electrolysis achieves the lowest energy in direct CO 2 electrolysis. • Catalyst and system integration approaches are key for CO 2 electrolysis. Renewable-electricity-powered CO 2 reduction (CO 2 R) could enable penetration of renewables into the vast chemical industry. Present-day CO 2 R technology realizes production of multi-carbon chemicals with industrially relevant rates (>100 mA cm −2 ). However, (bi)carbonate formation (2OH – + CO 2 → CO 3 2– + H 2 O), which occurs readily in systems based on neutral and alkaline electrolytes, results in CO 2 (reactant) loss and associated energy penalties that render the process unviable. This Review article focuses on the overview of carbon-efficient CO 2 R systems: CO 2 R with all-liquid-phase anodic process; acidic-media CO 2 R; local CO 2 regeneration from (bi)carbonate via bipolar systems; tandem CO 2 conversion; and CO 2 R from capture solutions. It analyses the current feasibility of each system, discusses the technical and scientific challenges associated with each strategy, and outlines future research directions toward carbon- and energy-efficient CO 2 electrolysis at scale. The Review article emphasizes that carbon-efficient CO 2 R systems eliminate (bi)carbonate formation and ensuing energy penalties. With the recent catalysis- and system-level breakthroughs, some of these systems (CO 2 R with all-liquid-phase anodic process, tandem CO 2 conversion, and acidic-media CO 2 R) outperform the conventional alkaline and neutral-media CO 2 R systems in terms of energy intensity. The Review article underscores that achieving breakeven energy intensity requires further energy efficiency improvements, calling for innovative electrocatalysis and system integration approaches.