pH-dependent redox hydrogen pump for electrochemical direct air capture of CO₂

Redox-mediated electrochemical DAC offers a promising, energy-efficient alternative to conventional thermal methods but faces challenges with the oxidative degradation of organic redox mediators in air. While multi-electrolyzer systems mitigate oxygen exposure and solvent loss, the use of common pH-independent redox limits further voltage reductions. To overcome the voltage limitation of pH-independent mediators in electrochemical DAC, this study introduces a new electrochemical DAC strategy utilizing a pH-dependent redox mediator, anthraquinone-2,7-disulfonic acid salt (AQDS), within a dual-electrolyzer system coupled with a hydrogen pump. The pH-dependent redox potential of AQDS lowers the electrolyzer voltage, enabling an actual energy consumption of 257 kJ mol^-1 CO₂.