Life cycle assessment of CO₂ conversion and storage in metal–CO₂ electrochemical cells

Researchers have proposed a family of electrochemical technologies that incorporate CO₂ as a gas cathode and alkali or alkaline earth metal anodes to exploit the high reactivity of CO₂ with these metals. Such proposed cells operate by converting gaseous CO₂ into solid carbonate, extracting value from CO₂ in the form of electricity, and fixing the CO₂ in solid form. Given the increasing number of these proof-of-concept studies, it is timely to critically examine the potential of such emerging technologies to reduce stationary point source emissions. Environmental life cycle assessment (LCA) during early research stages can inform important design decisions. In this study, we perform LCA on electrochemical conversion processes (ECPs) involving Li, Na, Mg, or Ca as a co-reactant with CO₂ sourced from a coal plant, evaluating differing scenarios. We find that a Na-based primary ECP configuration that integrates capture with conversion of coal plant CO₂ emissions to Na₂CO₃ can avoid almost 28% of emissions (and 74% under best-case conditions) that are typically associated with conventional production of the same carbonate and electricity. This represents a net emissions decrease of 435 kg CO₂-eq per 1 MWh of electricity delivered by the ECP, from a baseline of 1,105 kg CO₂-eq emitted without any mitigation strategies. In contrast, all ECPs in a rechargeable configuration result in increased emissions compared to the conventional baseline, unless the ECP system energy requirements are provided by renewables and the conventional system is assumed to have high emissions intensity.