Extrinsic and intrinsic factors for electrochemical reduction of carbon dioxide on heterogeneous metal electrocatalysts

Excessive CO2 emissions from the traditional consumption of fossil fuels have led to severe environmental and ecological issues, including global temperature rise, atmospheric carbon imbalance, and expansion of desertification. To address these challenges, various green technologies and remediation techniques aimed at reducing CO2 emissions are being implemented worldwide. Among them, the electrochemical reduction (ECR) of CO2 into value-added fuels and chemicals has emerged as a promising strategy to complete the anthropogenic carbon cycle and promote sustainable development. However, the ECR of CO2 faces several challenges, including the inherent properties of CO2, harsh reduction conditions, poor catalytic performance, limited catalyst efficiency and stability, intermediate properties, competitive side reactions, and low product selectivity. Addressing these challenges requires a comprehensive understanding of both the extrinsic and intrinsic factors that influence the reduction process. This review provides a detailed examination of these factors, along with insights into the reduction principles and reaction mechanisms for the ECR of CO2. Extrinsic factors include the reduction temperature, electrolyte type and concentration, reaction cell design, catalyst/mass loading, electrolyte pH, pressure, and applied potential. Intrinsic factors encompass the active site properties of electrocatalysts, binding strength between CO2 and the reduction intermediates on the catalyst surface, electroactive surface area, nanocatalyst dimension, surface structure, morphology, and composition of the electrocatalyst. Additionally, we discuss advanced influences, such as electric fields, surface strain, dangling bonds, structural defects, ionomers, and hydrophobicity of electrocatalysts. The role and impact of each factor are analyzed, with a particular focus on the stability, reduction efficiency, and selectivity of the electrocatalyst and the product distribution in the ECR of CO2. This review aims to provide valuable insights for advancing the design and optimization of efficient and selective electrocatalysts to effectively address global CO2 emissions.