High-voltage supercapacitive swing adsorption of carbon dioxide

Abstract

We report Supercapacitive Swing Adsorption (SSA) with garlic roots-derived activated carbon achieving a record adsorption capacity of 312 mmol/kg at a low energy consumption of 72 kJ/mol and high mass loadings (>30 mg/cm2) at 1 V. 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. Up to a voltage of 1.4 V there is only minor increase in energy consumption, and a sorption capacity of 524 mmol/kg at an energy consumption of 130 kJ/mol 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.

Scaling Supercapacitive Swing Adsorption of CO2 Using Bipolar Electrode Stacks

“…Gas flow rates were adjusted with the electrode pair number in the stacks to obtain the full adsorption of CO2 within same time range, and were 6 cc/min for 2 pairs, 16 cc/min for 4 pairs, 24 cc/m for 8 pairs and 36 cc/m for 12 pairs. Adsorptive and energetic performance metrics were calculated analogously to our previous publications [27][28][29][30][31] and can be found in the Supporting Information section S2. Prior to the gas separation experiments, the stacks were characterized by cyclovoltammetry in order to verify their expected capacitive behavior.…”

“…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.…”