In-situ CO2 capture outperforms conventional bulk pH-swing electrolyzers

Electrochemical CO2 capture via pH-swing electrolyzers offers a promising alternative to thermally driven amine scrubbing, yet mass transfer limitations at the gas-liquid interface remain a critical bottleneck limiting scalability. This work addresses this challenge through a novel reactor architecture integrating gas diffusion electrodes (GDE) to enable in-situ CO2 capture at the electrode surface. We systematically evaluated two flow regimes: the flow-by (diffusion dominated) and flow-through (convective gas transport) and compared their performance against conventional ex-situ setups including bulk bubbling and countercurrent scrubbing. Using 0.1 M 2,7-anthraquinone disulfonic acid (AQDS) as a model active redox carrier, the in-situ setup achieved 213.0 mL captured CO2 versus 152.2 mL for bulk one, representing a 39.9% volumetric gain. Energy consumption decreased from 86.1 kJ·mol−1 (bulk) to 66.7 kJ·mol−1 (in-situ), corresponding to 22.5% reduction. Finally, it demonstrated superior capture efficiency (43.7%), volumetric capacity (5.6 kgm−3) with minimum CO2 concentrations of 6.4% from a 10% feed stream compared to the ex-situ setups. Continuous operation over 96 h confirmed reversible cycling without performance degradation. These findings establish reactor engineering as the primary design variable for electrochemical capture systems, enabling substantial performance improvements independent of electrolyte optimization. The demonstrated scalability pathway provides actionable design principles for industrial CO2 capture applications across diverse source concentrations.