Work

Reversible CO2 Concentration in the Electrical Double Layer in the Absence of (Bi)carbonate

Year: 2026

Type: preprint

Abstract: The behaviour of CO 2 at electrode-electrolyte interfaces is key in the development of climate change mitigation technologies, such as electrochemical CO 2 capture and conversion. In particular, electrochemical CO 2 capture using supercapacitors, an approach known as supercapacitive swing adsorption (SSA), utilises the charging and discharging of supercapacitor devices to reversibly and selectively adsorb CO 2 . As supercapacitive charging incurs low energy losses and can be carried out under ambient conditions, this method has the potential to achieve higher energy efficiencies than other CO 2 capture techniques. However, the design of SSA systems has been hindered by a lack of understanding of the underlying mechanism. In particular, the contributions of different CO 2 -related species—molecular CO 2 , carbonate, and bicarbonate—to SSA remain poorly understood. In this work, the role of molecular CO 2 in SSA using activated carbon electrodes was explored in the absence of carbonate and bicarbonate ions by using an inert organic electrolyte solvent, acetonitrile. Interestingly, this system was capable of reversible electrochemical CO 2 adsorption, which demonstrated definitively that molecular CO 2 is a contributing active species in SSA. It was found that exchanging the gas headspace from N 2 to CO 2 increased the capacitance of both aqueous and acetonitrile-based supercapacitors. This was attributed to the accumulation of CO 2 (in acetonitrile) and/or CO 2 -derived anions (in water) at the electrode-electrolyte interface, modifying the properties of the dielectric and, therefore, influencing charge storage behaviour in the electrical double layer. This reversible concentration of CO 2 in the electrical double layer of supercapacitors presents opportunities for further development in electrochemical CO 2 capture and conversion technologies.

Source: ChemRxiv

DOI: 10.26434/chemrxiv.15008509/v1