Durable CO₂ conversion in the proton-exchange membrane system

Electrolysis that reduces carbon dioxide (CO₂) to useful chemicals can, in principle, contribute to a more sustainable and carbon-neutral future^1-6. However, it remains challenging to develop this into a robust process because efficient conversion typically requires alkaline conditions in which CO₂ precipitates as carbonate, and this limits carbon utilization and the stability of the system^7-12. Strategies such as physical washing, pulsed operation and the use of dipolar membranes can partially alleviate these problems but do not fully resolve them^11,13-15. CO₂ electrolysis in acid electrolyte, where carbonate does not form, has therefore been explored as an ultimately more workable solution^16-18. Herein we develop a proton-exchange membrane system that reduces CO₂ to formic acid at a catalyst that is derived from waste lead-acid batteries and in which a lattice carbon activation mechanism contributes. When coupling CO₂ reduction with hydrogen oxidation, formic acid is produced with over 93% Faradaic efficiency. The system is compatible with start-up/shut-down processes, achieves nearly 91% single-pass conversion efficiency for CO₂ at a current density of 600 mA cm^-2 and cell voltage of 2.2 V and is shown to operate continuously for more than 5,200 h. We expect that this exceptional performance, enabled by the use of a robust and efficient catalyst, stable three-phase interface and durable membrane, will help advance the development of carbon-neutral technologies.