A review on progress and perspective of molecular catalysis in photoelectrochemical reduction of CO2

The ever-increasing concentration of CO2 in the atmosphere has become an issue of grave concern mainly due to its adverse effect on the climate induced by the excessive greenhouse effect. Among the various possible mitigation strategies, utilization of CO2 for the production of commodity chemicals and fuel is a promising and environmentally friendly approach. However, the higher thermodynamic and kinetic stability of CO2 molecules requires extensive energy and extreme reaction conditions. In recent decades, alternative techniques like photocatalytic, electrocatalytic, and photo-electrocatalytic reduction of CO2 have been considered technically feasible, economically viable and environmentally friendly. Specifically, photoelectrocatalytic reduction of CO2 is highly important as it combines the advantages of photocatalysis and electrocatalysis such as use of renewable, inexhaustible solar energy, less electrical energy consumption, no sacrificial donor and higher conversion efficiency. This review systematically summarizes the recent advances in PEC CO2 reduction, primarily using molecular complexes of transition metals and their hybrids with semiconductors. After an initial discussion on the basic principal of PEC CO2 reduction, a detailed discussion of the different transition metal complexes, both mono-metallic and bimetallic of noble and non-noble metals, various process parameters for PEC CO2 reduction, along with the proposed mechanism and limitations are presented. In addition, the review highlighted the recent advancements in PEC CO2 reduction and critical evaluation of different issues to predict the direction to pursue the research for effective conversion of CO2 to valuable chemicals.