Where to address N2 and reactive impurities in the CO2 electrochemical value chain?

The utilization of CO 2 provides a decarbonization pathway for hard-to-abate emissions, with solid-oxide and low-temperature electrochemical CO 2 conversion offering routes to value-added chemicals. Unfortunately, CO 2 sources are dilute and contain reactive impurities (NO x /SO x /O 2 ) that influence electrolyzer performance. Research has then focused on understanding the implications of impurities on operation and designing catalyst structures that tolerate impure feeds. High feed tolerances would be promising as electrolyzers could then be co-located with point-source emissions and avoid pre-processing. However, electrolyzers operated with dilute or impurity-tolerant feeds merely transfer separation burdens downstream. Sulfur limits for methanol or Fischer-Tropsch synthesis are more stringent than the electrolysis step, while separating CO/N 2 downstream is more complex than separating CO 2 /N 2 upstream. Last, post-electrolysis oxygen impurities may pose flammability risks with by-product H 2 . In this perspective, we critically examine CO 2 feedstocks and invoke a higher-level discussion reflecting where reactive impurities should be addressed in the electrochemical value chain.