Recent Advances in Electrocatalytic Reduction of Carbon Dioxide Using Metal-Free Catalysts

Abstract

As part of the efforts to address the global energy issues, the identification of electrocatalysts for efficient and selective conversion of carbon dioxide to value-added products is a research topic of scientific and technological significance. Metal-free catalysts are considered next-generation, renewable materials that promise to be cost-effective, relative to their metal-containing counterparts, particularly relative to noble-metal-based catalysts. In this article, recent progress toward identification of metal-free catalysts for electrochemical reduction of carbon dioxide is reviewed. These catalysts are classified into four categories, including conducting polymers, pyridinium derivatives, aromatic anion radicals, and heteroatom-doped carbon materials. We provide a detailed investigation of the overall catalytic performance of each material, in terms of the product distribution, overpotential required, Faradaic yield, stability of the catalyst, and reaction mechanism. Several important factors that affect the catalytic performance, including the pH value, solvent type, carbon dioxide pressure/concentration, nature of the auxiliary electrode, and morphology of the catalyst, are discussed. The main issues and challenges associated with large-scale electrochemical reduction of carbon dioxide using metal-free catalysts are identified and analyzed, and future research directions for addressing these problems are suggested.