CO electroreduction favors carbon isotope C over C and facilitates isotope separation.

We discovered that CO electroreduction strongly favors the conversion of the dominant isotope of carbon (C) and discriminates against the less abundant, stable carbon C isotope. Both absorption of CO in the alkaline electrolyte and CO electrochemical reduction favor the lighter isotopologue. As a result, the stream of unreacted CO leaving the electrolyzer has an increased C content, and the depletion of C in the product is several times greater than that of photosynthesis. Using a natural abundance feed, we demonstrate enriching of the C 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 (C, N) essential to the healthcare and chemistry research, and to an economically viable, disruptive application of electrolysis technologies developed in the context of sustainability transition.