Activated Carbon Electrodes with Improved Sorption Capacity for Supercapacitive Swing Adsorption of Carbon Dioxide

Abstract

Global warming due to anthropogenic CO2 emissions demands the rapid development of efficient carbon capture technologies. Supercapacitive swing adsorption (SSA) is a technology that relies on the reversible charge and discharge of supercapacitor electrodes to selectively adsorb and desorb CO2. A current limitation of SSA is the low sorption capacity. Here, we investigate a series of activated carbons derived from biomass, coke, coal, and carbide as electrode materials for SSA. The energetic and adsorptive performance metrics are quantitatively analyzed and their relationship with double layer capacitance, real capacitance, imaginary capacitance, and diffusion resistance is studied. The results show that there is a strong positive correlation between specific capacitance and CO2 adsorption capacity. The highest gravimetric sorption capacity was measured for garlic-root derived activated carbons valuing 273 mmol.kg-1 for 4 cm2 electrodes having a specific capacitance of 257 F.g-1. This is a ~4-fold increase compared to BPL 4x6 carbon having a specific capacitance of 86 F.g-1 and an adsorption capacity of 70 mmol.Kg-1. Volumetric specific capacitances and volumetric sorption capacities are also correlated. The highest volumetric sorption capacity was found for garlic powder-derived activated carbon valuing 65.3 mol.m3 at a volumetric specific capacitance of 62.3 F.cm3 which is a two-fold increase compared to BPL 4x6 carbon which has a volumetric specific capacitance of 41.2 F/cm3 and a volumetric sorption capacity of 27.1 mol.m3. In addition, higher specific capacitance tends to improve the overall adsorption rate and productivity.

High-voltage supercapacitive swing adsorption of carbon dioxide

“…More than 2-fold improvement in volumetric sorption capacity is achieved compared to all previous reports. 15 The relationship between the total charge stored in the supercapacitors at different voltage windows and the gravimetric/volumetric sorption capacities also follows a linear pattern until -1.4 V (Figure S3). Above -1.5 V there is a possibility of carbon electrooxidation along with increased leakage currents and decreased coulombic efficiency, 26 which may reduce the adsorption capacity as well as adsorption rates.…”

“…The charge efficiency (CE) of GR-AC electrodes is around 0.3 up to -1.2 V which is higher than all the previously reported values. 15 The CE slightly reduces to 0.26 at -1.4 V, and further reduces to 0.21 at -1.6 V (Figure 3f). The improved charge efficiencies may be due to improved pore accessibility to H + /HCO3 -/CO3 2-, leading to a more effective removal of these ions from the chemical equilibrium.…”

“…These resistance values are lesser than all the previously reported biomass-derived electrodes used for SSA. 15 This signifies that the modified synthesis and electrode preparation procedure for garlic-roots derived activated carbon electrodes is critical to achieve better electronic conductivity. A record low energy consumption of ∼70 kJ.mol -1 is observed at -1 V voltage window (Figure 3e).…”

“…[11][12][13][14] Recently, our group discovered that biomass-derived activated carbons from garlic skin, garlic roots, and garlic clove powder lead to an increase of the gravimetric adsorption capacity by about four times (up to 273 mmol/kg) and the adsorption rate by about three times (up to 84 µmol.kg -1 s -1 ). 15 Around the same time, Forse et al reported that the gravimetric sorption capacity of SSA can be increased from 50 to 112 mmol.kg -1 by charging the electrodes between -1 V to +1 V instead of -1 V to 0 V, but this approach resulted in a very high energy consumption (751 kJ/mol CO2). 16 To meet the 2025 DOE cost target for post-combustion CO2 capture (∼ 40$/ton), 17 a significant decrease in SSA energy consumption and further increase in SSA adsorption capacity is desirable.…”

Scaling Supercapacitive Swing Adsorption of CO2 Using Bipolar Electrode Stacks

“…Cell voltage increase to 1.4 V further improved the sorption capacity to ~500 mmol/kg at an energy consumption of ~150 kJ/mol. The cycles were highly repeatable and reversible in tests lasting up to 130 h. 30,31 The adsorption in SSA is believed to occur through three possible mechanisms, the ionic liquidsolid mechanism, the molecular liquid-solid mechanism, and the molecular gas-solid mechanism. [27][28][29] In the ionic liquid-solid mechanism, the CO2 hydrolyzes in the aqueous electrolyte inside the activated carbon pores and adsorbs to the pore surfaces of the positive and negative electrode electrostatically in form of bicarbonate/carbonate anions, and protons, respectively.…”