Reduction of CO2 to chemicals and Fuels: Thermocatalysis versus electrocatalysis

Reducing carbon dioxide to valuable chemicals and fuels such as formic acid, carbon monoxide, methanol, methane, ethylene, ethanol, and multi-carbon (C2 + ) products by renewable hydrogen via thermocatalysis or by renewable electricity via electrocatalysis provides an attractive and sustainable way for achieving carbon abatement and addressing the climate change challenge. The thermocatalytic pathway is easy to scale up and realize industrial-scale applications, but some of the reactions are limited by kinetics, and/or thermodynamics equilibrium. In contrast, the electrocatalytic approach is less mature but has advantages, including lower temperature and lower pressure, using water as a hydrogen source, and no limitation from thermodynamic equilibrium. However, the electrocatalysis process requires the development of more effective and stable electrocatalysts. In this review, the latest progress in converting CO2 to various chemicals or fuels via thermocatalysis and electrocatalysis is summarized and compared with an emphasis on catalysts and reaction mechanisms. The similarities and differences between thermocatalysts and electrocatalysts as well as the thermocatalytic process and electrocatalytic process are discussed and compared in detail. The combination of strength between thermocatalysis and electrocatalysis is also introduced and discussed. Future research directions for the CO2 conversion process are outlined.