Durable CO conversion in the proton-exchange membrane system.

Electrolysis that reduces carbon dioxide (CO) to useful chemicals can, in principle, contribute to a more sustainable and carbon-neutral future. However, it remains challenging to develop this into a robust process because efficient conversion typically requires alkaline conditions in which CO precipitates as carbonate, and this limits carbon utilization and the stability of the system. Strategies such as physical washing, pulsed operation and the use of dipolar membranes can partially alleviate these problems but do not fully resolve them. CO electrolysis in acid electrolyte, where carbonate does not form, has therefore been explored as an ultimately more workable solution. Herein we develop a proton-exchange membrane system that reduces CO 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 CO 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 CO at a current density of 600 mA cm 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.