Benchmarking Performance Indices of Electrochemical CO2 Reduction to Ethylene Based on Prospective Life Cycle Assessment for Negative Emissions

To mitigate global warming to the most ambitious targets, it is necessary to remove CO2 from the atmosphere and reduce fossil fuels use. The electrochemical conversion of CO2 to ethylene (C2H4) as a basic chemical is a promising technology that meets both requirements; however, its life cycle CO2 emissions remain inconclusive because of varying assumptions in the performance indices. This study aimed to set benchmarks for the four most sensitive indices to achieve -0.5 t-CO2/t-C2H4 by calculating net greenhouse gas (GHG) emissions through a prospective life cycle assessment of a model system including CO2 capture, CO2 enrichment, electrochemical conversion, CO2 recycling, and cryogenic separation. As a result, the electrochemical conversion process was the hotspot of life cycle emissions, and representative benchmarks were determined as follows: cell voltage, 3.5 V; C2H4 Faraday efficiency, 70%; conversion rate, 20%; and electrochemical CO2 recycling energy, 2.2 GJ/t-CO2. The gaps between the benchmarks and current top data of cell voltage and Faraday efficiency were <10%, and suppressing the performance degradation for up to one year was found to be a critical requirement. These results can direct research towards the development of a year-round stable system, rather than further improving the performance indices.