Abstract:

Over the past decades, advances in science and technology have greatly benefitted the society. However, the exploitation of fossil fuels and excessive emissions of polluting gases have disturbed the balance of the normal carbon cycle, causing serious environmental issues and energy crises. Global warming caused by heavy CO₂ emissions is driving new attempts to mitigate the increase in the concentration of atmospheric CO₂. Significant efforts have been devoted for CO₂ conversion. To date, the electroreduction of CO₂, which is highly efficient and offers a promising strategy for both storing energy and managing the global carbon balance, has attracted great attention. In addition, the electrosynthesis of value-added C₂₊ products from CO₂ addresses the need for the long-term storage of renewable energy. Therefore, developing catalysts that function under ambient conditions to produce C₂ selectively over C₁ products will increase the utility of renewable feedstocks in industrial chemistry applications. Recently, great progress has been made in the development of materials for electrocatalytic CO₂ reduction (ECR) toward C₂₊ products; however, some issues (e.g., low selectivity, low current efficiency, and poor durability) remain to be addressed. In addition, the elementary reaction mechanism of each C₂₊ product remains unclear, contributing to the blindness of catalyst design. In this regard, the development of proposed mechanisms of ECR toward C₂₊ products is summarized herein. The key to generating C₂₊ products is improving the chances of C―C coupling. Test conditions significantly influence the reaction path of the catalyst. Thus, three different paths that that are most likely to occur during ECR to C₂₊ products are proposed, including the CO, CO-COH, and CO-CO paths. In addition, typical material regulatory strategies and technical designs for ECR toward C₂₊ products (e.g. crystal facet modulation, defect engineering, size effect, confinement effects, electrolyzer design, and electrolyte pH) are introduced, focusing on their effects on the selectivity, current efficiency, and durability. The four strategies for catalyst design (crystal facet modulation, defect engineering, size effect, and confinement effect) primarily affect the selectivity of the ECR via adjustment of the adsorption of reaction intermediates. The last two strategies for technique design (electrolyzer design and electrolyte pH) contributing greatly toward improving the current efficiency than selectivity. Finally, the challenges and perspectives for ECR toward C₂₊ products and their future prospects are discussed herein. Therefore, breakthroughs in the promising field of ECR toward the generation of C₂₊ products are possible when these catalyst design strategies and mechanisms are applied and novel designs are developed.

Key words: CO₂ electroreduction, High value-added product, Selectivity, Faradaic efficiency, Durability