High‐Voltage Supercapacitive Swing Adsorption of Carbon Dioxide

Abstract

Supercapacitive swing adsorption (SSA) with garlic roots‐derived activated carbon achieves a record adsorption capacity of 312 mmol kg−1 at a low energy consumption of 72 kJ mol−1 and high mass loadings (>30 mg cm−2) at 1.0 V for 85%N2/15%CO2 mixtures. The activated carbons are inexpensively prepared in a one‐step process using potassium carbonate, and air as activators. The adsorption capacity further increases with increasing voltage. At a voltage of 1.4 V, a sorption capacity of 524 mmol kg−1 at an energy consumption of 130 kJ mol−1 can be achieved. The volumetric sorption capacity is also enhanced and reaches values of 85.7 mol m−3 at 1.0 V, and 126 mol m−3 at 1.4 V. Cycle stability for at least 130 h is demonstrated.

Impacts of supercapacitor electrode structure on electrochemical CO2 capture

“…In these experiments, the electrochemical cell was charged to a cell voltage of -0.8 V ("negative charging mode", the gas-exposed electrode is negatively charged) or + 0.8 V ("positive charging mode", the gas-exposed electrode is positively charged) with constant current charging (and discharging) and 5-min voltage holds between charge and discharge. Similar to previous studies, [16][17][18]22 CO2 capture is observed upon negative charging to -0.8 V (Figure 2C). Upon cell discharging back to 0 V CO2 release is then observed, with the behaviour repeatable over several cycles.…”

“…Recent work has begun to optimise electrode materials, 18 electrolyte composition 19,20 and charging protocols. 17,21,22 Most notably, a recent study showed that activated carbon electrodes with higher electrochemical capacitances could achieve higher CO2 capture capacities and rates approaching 270 mmolCO2 kg -1 and 300 mmolCO2 kg -1 h -1 , respectively. 18 Despite this progress, it remains unclear how the specific electrode structure (e.g., surface area, pore size, surface functional groups, etc.)…”

Enhancing Supercapacitive Swing Adsorption of CO2 with Advanced Activated Carbon Electrodes

“…Our group reported an energy consumption of ≈100 KJ mol −1 with 78% energy efficiency using 7 cm BPL‐AC electrodes in 5 M NaCl and 1 M MgBr 2 electrolyte, arguing that improved energy consumption may be achievable by use of 5 M NaCl, or 1 M MgBr 2 . [ 57 ] More recently, we reported energy consumption values of ≈70 KJ mol −1 using hot‐pressed garlic‐roots derived electrodes, [ 58 ] arguing that development of new electrode materials is another promising route to further minimize the energy consumption values.…”

Supercapacitive Swing Adsorption of Carbon Dioxide: Current Status and Perspectives

“…In addition, it was found that appropriately increasing the charging voltage can increase the CO 2 adsorption capacity, but this will increase energy consumption, and excessive charging voltage will reduce capacitance performance. Li et al [72] employed the garlic roots activated carbon electrode, expanding the negative charging voltage from À 1.0 V to À 1.4 V, the energy consumption increased only slightly (130 kJ mol À 1 ), and a high CO 2 adsorption capacity of 461 mmol kg À 1 was achieved, which was greatly improved compared with the CO 2 adsorption capacity (312 kJ mol À 1 ) obtained from À 1.0 V negative charging, in addition to the high specific capacitance and stable SSA performances of the garlic roots activated carbon as shown in Figure 12(a). In the experiment with a gas flow rate of 5 sccm (standard cubic centimeter per minute), and a charging voltage from 0 to À 1.4 V a higher CO 2 adsorption capacity of 524 mmol kg À 1 was obtained as shown in Figure 12(b).…”