Prospective Life Cycle Assessment Bridging Biochemical, Thermochemical, and Electrochemical CO2 Reduction toward Sustainable Ethanol Synthesis

Faced by the concerning climate change worldwide and agriculture-dependent biochemical and energy-intensive thermochemical technologies, research and development efforts in exploring sustainable ethanol synthesis toward carbon neutrality are urgent. Recently, an electrochemical process via the electrocatalytic CO2 reduction reaction (CO2RR) to synthesize ethanol has emerged as a promising alternative approach by directly consuming CO2 from the atmosphere. Despite the fact that numerous remarkable electrocatalysts with fascinating activity, selectivity, and stability have been extensively uncovered in this field, environmental impacts of this technology have rarely been acknowledged. Herein, a life cycle assessment (LCA) study is conducted to evaluate the potential environmental impacts and benefits of an innovative electrochemical process versus conventional biochemical and thermochemical processes toward the sustainable synthesis of 1 kg of ethanol. Impact assessment results revealed that with the contemporary electricity mix, the electrochemical process is still surpassed by the biochemical process, and its environmental benignity is not pronounced, attributed to tremendous electricity utilities accounting for 67.7-100% of impacts. However, it prevails over the two conventional routes when powered by renewable energies, particularly solar energy, with impact reduction ranging from 108.6 to 750.5%, while providing the greatest benefits with respect to terrestrial ecotoxicity (TETP). Carbon footprint further indicates that the electrochemical process becomes competitive and reaches carbon neutrality once driven by electricity with carbon intensity (CI) below 0.25 and 0.12 kg CO2 eq/kWh. Overall, in spite of its massive electricity utilities, the electrochemical ethanol synthesis route is highly promising in environmental impact remediation when coupled with renewable energies, which calls for more efforts from researchers and governments to achieve carbon neutrality and sustainability in years to come.