Activated Carbon Electrodes with Enhanced Supercapacitive Swing Adsorption of Carbon Dioxide

Abstract

Activated carbon electrodes with enhanced supercapacitive swing adsorption of carbon dioxide The necessity to achieve net-zero emission of anthropogenic CO2 by the end of the twenty first century has recently raised interest among researchers to develop electrochemical CO2 capture technologies due to their high selectivity, low energy consumption, and ease to be powered with renewable electricity. Currently, most of these technologies rely on the use of expensive adsorbing electrode materials, and ion-selective membranes.1 Supercapacitive swing adsorption (SSA) is a technique that only requires activated carbon electrodes, a separator, and an aqueous electrolyte to capture and concentrate CO2 during the capacitive charging and discharging of carbon electrodes, making it attractive from the cost and environmental perspective.2 Recent studies on SSA focused on improving the energetic and adsorptive performance by tuning the electrolyte concentration, composition, and electrode charging protocols.3 However, the adsorption capacity stayed around 100 mmol/kg (compared to ∼1000 mmol/kg for amine scrubbing) even at higher electrolyte concentrations and extended voltage windows.2,4 Herein, we report high surface area activated carbon electrodes derived from biomass, coke, coal, and carbide for SSA. We find a strong correlation between capacitance and CO2 adsorption capacity and quantitatively analyze the energetic and adsorptive performance of different electrode materials. Biomass-derived garlic roots-derived activated carbon (GR-AC) electrodes show 4-fold enhanced adsorption capacity (270 mmol/kg) and 3.2-fold enhanced adsorption rate (84 μmol.kg-1.s-1) compared to state-of-the-art coal-derived carbon. However, GR-AC electrodes showed an energy consumption of 179 kJ/mol. Modifying the activation treatment from KOH-based two-step process to K2CO3-based one-step process yielded micro-mesoporous activated carbon. Warm-pressed electrodes from this carbon showed lower energy consumption (72 kJ/mol) and improved gravimetric/volumetric adsorption capacity (312 mmol/kg and 86 mol/m3). Increasing the voltage window from 1 V to 1.6 V resulted in even higher adsorption capacity (524 mmol/kg at -1.4 V and 578 mmol/kg at -1.6 V) as well as improved gas purity (Figure 1). Cyclic voltammetry and electrochemical impedance spectroscopy confirmed the capacitive-type behavior of electrodes up to 1.4 V.Figure 1 Voltage response (black) and CO2 concentration changes (blue) at different voltage windows References R. Sharifian, R. M. Wagterveld, I. A. Digdaya, C. Xiang, and D. A. Vermaas, Energy Environ. Sci., 14, 781–814 (2021).S. Zhu, J. Li, A. Toth, and K. Landskron, ACS Appl. Energy Mater., 2, 7449–7456 (2019).M. Rahimi, A. Khurram, and T. A. Hatton, Chem Soc Rev (2022).T. B. Binford, G. Mapstone, I. Temprano, and A. C. Forse, Nanoscale (2022). Figure 1