(478d) Characterization of a Pilot-Scale Supercapacitive Swing Adsorption (SSA) for Direct Air Capture of CO2

Supercapacitive swing adsorption (SSA)¹ is an electrochemical-based method of CO₂ capture and release based on charging and discharging supercapacitors. In the basic setup of SSA shown in Figure 1, a supercapacitive electrode is partially exposed to CO₂-containing gas and the other electrode is completely saturated with electrolyte. CO₂ is selectively adsorbed from the gas stream when the supercapacitor is charged, and desorption occurs upon discharge. In contrast to redox-based CO₂ sorption techniques, SSA relies on the electrostatic attraction of CO₂-derived species at the electric double layer that results from the application of a potential difference across the cell. SSA therefore has the advantage of faster charge-discharge rates, longer cycle life and higher roundtrip efficiencies over redox-based alternatives. Furthermore, the SSA process runs under mild conditions, without the additional operational costs associated with thermal and pressure swing adsorption.

Recent experimental SSA research has focused on synthesizing biomass-based supercapacitive electrodes with very high adsorption capacities², and characterizing the effects of charging protocols³, electrolyte composition⁴, potential oxygen interaction, on CO₂ adsorption from flue gas (15% CO₂, 85% N₂) and in direct air (400 part per million CO₂) capture (DAC) applications. Initial results suggest SSA is relatively insensitive to the choice of electrolyte, and a negative charging protocol results in a lower energy consumption than positive charging. Also, there is a short term, positive correlation between CO₂ adsorption and oxygen in the inlet gas stream. However, the concept of SSA needs to be demonstrated at pilot scale to verify its performance and for eventual scale-up for real-world commercial deployment. Furthermore, the eventual optimization of an SSA process is currently limited by the lack of clarity on the exact mechanism of CO₂ hydrolysis and potential side reactions involved in the adsorption and desorption steps.

In this work, we demonstrate an automated, scalable, four-stage semi-batch SSA process illustrated in Figure 2 for DAC. In this new architecture, the gas stream is systematically directed through valves and an extraction pump that are controlled by a Python-based logic on a central microprocessor, thus controlling the extent of CO₂ adsorption and desorption. This new experimental set-up enables the verification (or otherwise) of previous experimental findings and provides information on a previously un-examined performance metric - the purity of extracted CO₂. Experimental results and insights that are validated with this new architecture will reinforce our understanding of the SSA process, enable optimization and ultimately foster the development of commercial SSA applications for DAC.

References

1. Kokoszka B, Jarrah NK, Liu C, Moore DT, Landskron K. Supercapacitive swing adsorption of carbon dioxide. Angewandte Chemie International Edition. 2014;53(14):3698–3701.
2. Bilal M, Li J, Landskron K. Enhancing Supercapacitive Swing Adsorption of CO2 with Advanced Activated Carbon Electrodes. Advanced Sustainable Systems. 2023;7(11):2300250.
3. Binford TB, Mapstone G, Temprano I, Forse AC. Enhancing the capacity of supercapacitive swing adsorption CO 2 capture by tuning charging protocols. Nanoscale. 2022;14(22):7980–7984.
4. Zhu S, Li J, Toth A, Landskron K. Relationships between the Elemental Composition of Electrolytes and the Supercapacitive Swing Adsorption of CO2. ACS Applied Energy Materials. 2019;2(10):7449–7456.