Benchmarking Performance Indices of Electrochemical CO 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 CO from the atmosphere and reduce fossil fuels use. The electrochemical conversion of CO to ethylene (CH) as a basic chemical is a promising technology that meets both requirements; however, its life cycle CO 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-CO/t-CH by calculating net greenhouse gas (GHG) emissions through a prospective life cycle assessment of a model system including CO capture, CO enrichment, electrochemical conversion, CO 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; CH Faraday efficiency, 70 %; conversion rate, 20 %; and electrochemical CO recycling energy, 2.2 GJ/t-CO. 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.