A Review of Photochemical and Electrochemical CO2 Valorization: Current Progress and Future Perspectives for Re-envisioning Carbon

Abstract The elevated level of carbon dioxide (CO2), accompanied by additional greenhouse gases (GHGs) due to increased anthropogenic activities, highlights major obstacles in the quest for a clean-energy future. The chemical transformation of CO2 into value-added products exhibits the ability to reduce carbon emissions. Therefore, confronting the challenges of escalated climate change coupled with energy shortages, synthesizing affordable and efficient catalysts for the CO2 valorization into sustainable products constitutes a viable redressal. The review deals with the process of CO2 reduction by photochemical and electrochemical methods, displaying superior performance and carbon-free energy policies, which align well with the environmental impact. The conversion of solar energy into storage-stable molecular bonds is widely acknowledged through sunlight-driven CO2 reduction, whereas electrochemically driven CO2 valorization generates electricity from various sustainable renewable energy resources to further coalesce captured CO2 into high-value compounds, including methanol, ethylene, methane, carbon monoxide, acetate, and formic acid. The study shows that the kinetically controlled step in the net CO2 reduction has a significant role in the evolution direction and in facilitating sustainable energy production of carbon-containing intermediates derived from a proton-electron-coupled process. Further, the two different types of electrodes have been discussed for converting CO2 into valuable products. A section has been dedicated to analyzing converted products employing different spectroscopic methodologies, for instance, high-performance liquid chromatography, gas chromatography, and nuclear magnetic resonance. Also, their performance has been assessed by reporting quantum yield, turnover frequency (TOF), turnover number (TON), and selectivity. Lastly, the various challenges and perspectives are discussed and concluded with a precise conclusion.