Metallic nanocatalysts for electrochemical CO₂ reduction in aqueous solutions

How to effectively and efficiently reduce carbon dioxide (CO₂) to value-added chemicals represent a frontier in catalysis research. Due to the high activation energy needs and the endothermic nature of CO₂ reduction, the reactions are difficult to carry out. When H₂O is present, hydrogen evolution reactions (HER) often compete favorably with CO₂ reduction reactions. For these reactions, catalysts are of critical importance to CO₂ reduction. In this article, we review the various metal nanocatalysts for electrochemical CO₂ reduction (ECR) reactions. In recognition of the importance of H₂O to CO₂ reduction, we focus our discussions on systems in aqueous solutions. Nanostructured metal catalysts are chosen for the discussions because they represent the most effective catalysts for ECR. After a brief introduction of the fundamental principles of ECR, we devote the rest of the article on the discussions of various types of nanostructured metallic catalysts, which are categorized by their compositions and working mechanisms. Lastly, strategies for improving reaction efficiency and selectivity are discussed.