Electrochemical CO₂ reduction with ionic liquids: review and evaluation

The increasing CO₂ emission, as the chief culprit causing numerous environmental problems, could be addressed by the electrochemical CO₂ reduction (CO₂R) to the added-value carbon-based chemicals. Ionic liquids (ILs) as electrolytes and co-catalysts have been widely studied to promote CO₂R owing to their unique advantages. Among the potential products of CO₂R, those only containing one carbon atom, named C1 products, including CO, CH₃OH, CH₄, and syngas, are easier to achieve than others. In this study, we first summarized the research status on CO₂R to these C1 products, and then, the state-of-the-art experimental results were used to evaluate the economic potential and environmental impact. Considering the rapid development in CO₂R, future scenarios with better CO₂R performances were reasonably assumed to predict the future business for each product. Among the studied C1 products, the research focuses on CO, where satisfactory results have been achieved. The evaluation shows that producing CO via CO₂R is the only profitable route at present. CH₃OH and syngas of H₂/CO (1 : 1) as the targeted products can become profitable in the foreseen future. In addition, the life cycle assessment (LCA) was used to evaluate the environmental impact, showing that CO₂R to CH₄ is the most environmentally friendly pathway, followed by the syngas of H₂/CO (2 : 1) and CO, and the further improvement of the CO₂R performance can make all the studied C1 products more environmentally friendly. Overall, CO is the most promising product from both economic and environmental impact aspects.