Supercapacitor-based CO2 capture enhanced by electrolyte pH control

Abstract

Supercapacitive swing adsorption (SSA) is emerging as an energy-efficient alternative to traditional thermally-driven CO₂ capture technologies. While a range of operational factors have been actively explored to increase understanding of this technology, SSA is currently constrained by low CO₂ capture rates. In this work, we investigate how electrochemical CO₂ capture responds to changes in electrolyte pH by combining galvanostatic CO₂ adsorption measurements with quantitative solid-state ¹³C-NMR spectroscopy. Our measurements show 30% higher adsorption rates for basic electrolytes than for neutral electrolytes. In contrast, in an acidic electrolyte, we see substantially lower adsorption rates and capacities. To probe the origin of these observations, we use ¹³C NMR spectroscopy on uncharged electrolyte-soaked electrodes to examine CO₂ speciation. While dissolved CO₂ is detected across all electrolytes, bicarbonate concentrations increase with increasing initial electrolyte pH (i.e. the pH), before any reaction-induced pH changes occur, suggesting a bicarbonate- or pH-swing driven mechanism. Overall, our study provides additional insights into the factors governing CO₂ capture in SSA by highlighting the role of CO₂ speciation and electrolyte pH in optimising device performance.