CO₂ electroreduction favors carbon isotope ¹²C over ¹³C and facilitates isotope separation

We discovered that CO₂ electroreduction strongly favors the conversion of the dominant isotope of carbon (¹²C) and discriminates against the less abundant, stable carbon ¹³C isotope. Both absorption of CO₂ in the alkaline electrolyte and CO₂ electrochemical reduction favor the lighter isotopologue. As a result, the stream of unreacted CO₂ leaving the electrolyzer has an increased ¹³C content, and the depletion of ¹³C in the product is several times greater than that of photosynthesis. Using a natural abundance feed, we demonstrate enriching of the ¹³C fraction to ∼1.3% (i.e., +18%) in a single-pass reactor and propose a scalable and economically attractive process to yield isotopes of a commercial purity. Our finding opens pathways to both cheaper and less energy-intensive production of stable isotopes (¹³C, ¹⁵N) essential to the healthcare and chemistry research, and to an economically viable, disruptive application of electrolysis technologies developed in the context of sustainability transition.