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CO₂ utilization is the conversion of captured carbon dioxide into products that have economic value, so that the gas becomes a feedstock rather than a waste to be disposed of. It is distinct from carbon capture and storage in that the carbon is retained in the economic cycle, and distinct from simple reuse in that the molecule is chemically transformed; whether a given route reduces emissions at all depends on the energy source, the concentration of the feed and the lifetime of the product, since most routes are net consumers of energy. Electrochemical reduction is one of the more flexible options because the product is selected by the catalyst and the potential, and the reaction has been operated both in batch and continuously ^[1]. Solid sorbents that both capture and activate the molecule shorten the route, natural porous nanorods being one material that does both ^[2]. Coupling capture and conversion in a single process avoids the energy penalty of releasing the gas again, and integrated schemes convert the captured carbon directly to methane with high selectivity ^[3]. Conversion to organic molecules follows the same logic. Combining capture with thermal catalytic conversion, including from dilute sources, air among them, is now an active area ^[5]. Scale and the cost of hydrogen remain the dominant constraints.