Insights and Progress on Photocatalytic and Photoelectrocatalytic Reactor Configurations and Materials for CO2 Reduction to Solar Fuels

Excessive greenhouse gas (GHG) emissions arising from nonrenewable fossil fuel utilization are causing serious climate change. Since carbon dioxide (CO2) contributes about 76% of GHGs in the atmosphere, utilization of CO2 could reduce its negative impact on the environment. Among the technologies available for CO2 conversion, photocatalytic (PC) and photoelectrocatalytic (PEC) reduction of CO2 into valuable solar fuels have made significant progress. These two technologies are environmentally friendly and effective in concurrently solving energy crises. Insights on the principles, thermodynamics, and limitations of photocatalysis/photoelectrocatalysis using sustainable energy for reducing CO2 are elucidated in this review. The configurations of cathode-anode and the proton exchange membrane in PEC membrane reactors are discussed. The advances of photoelectrocatalysts such as titania, copper oxides, complex metal-organic frameworks (MOFs), membrane-based immobilized, and metallic photoelectrocatalysts for PEC reduction of CO2 are also incorporated. Discussion of possible reaction mechanisms using DFT simulation to postulate feasible pathways occurring on catalyst surfaces is presented. It is recognized that PEC CO2 reduction is critical in the utilization of CO2 and solar energy research. It is also deduced that advances in reactor configurations along with photoelectrocatalyst materials are vital in mitigating excess CO2 emissions to generate solar fuels.