Kai Landskron

The mechanism of supercapacitive swing adsorption (SSA) has been investigated by pH measurements and acid‐base titrations of water‐extracted, charged activated carbon electrodes at voltage windows varying from 0–0.5 to 0–1.4 V. 15%CO ₂ /85%N ₂ mixtures and pure N ₂ were used as feed gases. Deionized water extracts from negatively charged electrodes showed a pH increase for both feed gases. Titration of extracts from negative electrodes exposed to CO ₂ consumed more HCl titrant compared to those without CO ₂ . Conversely, extracts from the positive electrodes consumed more KOH titrant when only N ₂ was present. The pH values and titrant amounts consumed increased with increasing voltage window for both electrodes. Larger amounts of acid consumed for negative electrode extracts in the experiments with CO ₂ are explained by the adsorption of additional protons created from CO ₂ hydrolysis. Smaller amounts of base are consumed for the positive electrode in the presence of CO ₂ due to the reaction of bicarbonate with acid generated at the positive electrode. The results explain that CO ₂ is adsorbed to the negative electrode and desorbed from the positive electrode upon charging. They are evidence for the ionic liquid–solid mechanism of SSA, which assumes that CO ₂ sorption is driven by selective proton adsorption to the negative electrode.

The temperature-dependent solubility of boron nitride (BN) in sodium (Na) containing supercritical ammonia (NH3) was previously demonstrated. This study explores the temperature–dependent solubility of BN with other basic mineralizers (alkali metals lithium (Li) and potassium (K), and alkaline-earth metals magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba)) over a pressure range of 156—202 MPa. Additionally, this study analyzes the temperature dependence of BN solubility with a Na mineralizer, at lower pressures (from 81—118 MPa). Solubility measurements were performed on a gravimetric basis and normalized to the initial fill amount of ammonia or the indirectly, experimentally measured concentration of ammonia in the autoclave at the end of the hot, dwell conditions. All investigated mineralizers exhibited normal solubility of BN with respect to temperature achieving solubilities close to but slightly below that of Na in all cases except Ba for which equal solubility was observed. Magnesium and Ca exhibited the lowest solubilities approximately an order of magnitude lower than Ba. For Na, a decrease in autoclave pressure yielded a decrease in the normalized BN solubility (for both fill and dwell ammonia).

The mechanism of Supercapacitive Swing Adsorption (SSA) has been investigated by pH measurements and acid-base titrations of water-extracted, charged activated carbon electrodes at voltage windows varying from 0-0.5V and 0-1.4V. 15%CO2/85%N2 mixtures and pure N2 were used as feed gases. Deionized water extracts from negatively charged electrodes showed a pH increase for both feed gases. The titration of extracts from the negative electrodes exposed to CO2 consumed more HCl titrant compared to those without CO2. Contrary, the extracts from the positive electrodes consumed more KOH titrant when only N2 was present. The pH values and titrant amounts consumed increased with increasing voltage window for both electrodes. The larger amounts of acid consumed for the negative electrode extracts in the experiments with CO2 is explained by the adsorption of additional protons created from CO2 hydrolysis. The smaller amount of base consumed for the positive electrode in the presence of CO2 is due to reaction of bicarbonate with the acid generated at the positive electrode and conversion into gaseous CO2. The results explain that CO2 is adsorbed to the negative electrode and desorbed from the positive electrode upon charging. They are evidence for the ionic liquid–solid mechanism of SSA which assumes that CO2 sorption is driven by selective proton adsorption to the negative electrode.

Supercapacitive Swing Adsorption has been investigated for Direct Air capture applications. Experiments have been carried out with three different activated carbon electrode pairs derived from garlic roots at -1V and with 1M MgCl2 as electrolyte using 400 ppm CO2 in N2 as the gas mixture. Sorption capacities between 30 and 37 mmol/kg have been measured which is about six times smaller compared to benchmark experiments with a 15%CO2/85%N2 gas mixture. The weak dependency of the sorption capacity from CO2 partial pressure can be explained by the ionic liquid-solid mechanism which is based on strong electrostatic forces between the electrodes and ions formed from CO2 hydrolysis. The adsorption rates are about an order of magnitude smaller for 400 ppm CO2 compared to 15% CO2 due to the higher impact of gas flow rates and greater CO2 dilution. The energy consumption varies between 492 and 697 kJ/mol which is an increase of a factor of 9-12 compared to the 15% CO2/85% N2 gas mixture. The higher energy consumption is mainly due to the lower sorption capacity and the longer potential holding times needed at 400 ppm CO2.

We report on the supercapacitive swing adsorption (SSA) of carbon dioxide at different voltage windows in the presence of oxygen using activated carbon electrodes, and deliquescent, aqueous electrolytes. The presence of O₂ in the CO₂/N₂ gas mixture results in an up to 11 times higher CO₂ adsorption capacity with 3 M MgBr₂ (at 0.6 V) and up to 4–5 times higher adsorption capacity with 3 M MgCl₂ (at 1 V). A tradeoff between high CO₂ adsorption capacities and lower coulombic efficiencies was observed at voltages above 0.6 V. The energetic and adsorptive performance of the electrodes in the presence of oxygen below 0.5 V was similar to the performance with a CO₂/N₂ mixture without oxygen at 1 V. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the electrodes demonstrate that the specific capacitance increases while the diffusion resistance decreases in the presence of oxygen. Oxygen concentrations ranging between 5–20 % give similar energetic and adsorptive performance. The electrodes exhibit stable performance for up to 100 cycles of operation.

We report on the supercapacitive swing adsorption (SSA) of carbon dioxide at different voltage windows in the presence of oxygen using activated carbon electrodes, and deliquescent, aqueous electrolytes. The presence of O₂ in the CO₂/N₂ gas mixture results in an up to 11 times higher CO₂ adsorption capacity with 3 M MgBr₂ (at 0.6 V) and up to 4–5 times higher adsorption capacity with 3 M MgCl₂ (at 1 V). A tradeoff between high CO₂ adsorption capacities and lower coulombic efficiencies was observed at voltages above 0.6 V. The energetic and adsorptive performance of the electrodes in the presence of oxygen below 0.5 V was similar to the performance with a CO₂/N₂ mixture without oxygen at 1 V. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the electrodes demonstrate that the specific capacitance increases while the diffusion resistance decreases in the presence of oxygen. Oxygen concentrations ranging between 5–20 % give similar energetic and adsorptive performance. The electrodes exhibit stable performance for up to 100 cycles of operation.

Supercapacitive swing adsorption (SSA) modules with bipolar stacks having 2, 4, 8, and 12 electrode pairs made from BPL 4 × 6 activated carbon are constructed and tested for carbon dioxide capture applications. Tests are performed with simulated flue gas (15%CO₂ /85%N₂) at 2, 4, 8, and 12 V, respectively. Reversible adsorption with sorption capacities (≈58 mmol kg⁻¹) and adsorption rates (≈38 µmol kg⁻¹ s⁻¹) are measured for all stacks. The productivity scales with the number of cells in the module, and increases from 70 to 390 mmol h⁻¹ m⁻². The energy efficiency and energy consumption improve with increasing number of bipolar electrodes from 67% to 84%, and 142 to 60 kJ mol⁻¹, respectively. Overall, the results show that SSA modules with bipolar electrodes can be scaled without reducing the adsorptive performance, and with improvement of energetic performance.

We report enhanced supercapacitive swing adsorption (SSA) of carbon dioxide in the presence of oxygen using activated carbon electrodes, and deliquescent, aqueous electrolytes. The presence of O2 in the gas mixture results in up to 11 times increased CO2 adsorption capacity with 3M MgBr2 and up to 4-5 times increased adsorption capacity with 3M MgCl2. Varying the oxygen concentration (5-20% O2) does not affect the energetics and adsorptive performance. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the electrodes demonstrate that the specific capacitance increases while the diffusion resistance decreases in the presence of oxygen, indicating enhanced pore wettability, and the reversible formation of oxygen functionalities on the pore surfaces, which enhance the adsorption. The electrodes show good performance for more than 100 hours of operation.

Global warming due to anthropogenic CO₂ emissions argues for the rapid development of efficient carbon capture technologies. Supercapacitive swing adsorption (SSA) is a gas separation technology that relies on the reversible charge and discharge of supercapacitor electrodes to absorb and desorb CO₂ highly selectively and reversibly. However, thus far SSA only showed low sorption capacity, and slow sorption kinetics. Herein, it is shown that the sorption capacity can be substantially increased via the use of carbons with a higher specific capacitance. The highest gravimetric sorption capacity is measured with electrodes made from garlic‐roots derived activated carbon valuing 273 mmol kg⁻¹ having a specific capacitance of 257 F g⁻¹. In addition, the overall adsorption rate and productivity are improved. Cycling the electrodes for over 100 h showed highly reproducible, reversible CO₂ adsorption and desorption behavior. A preliminary technoeconomic and sensitivity analysis is provided to demonstrate the potential of SSA for commercial applications.

Global warming due to anthropogenic CO2 emissions argues for the rapid development of efficient carbon capture technologies. Supercapacitive swing adsorption (SSA) is a gas separation technology that relies on the reversible charge and discharge of supercapacitor electrodes to adsorb and desorb CO2 highly selectively and reversibly. However, thus far SSA only showed low sorption capacity of 70 mmol/kg, and slow sorption kinetics. Herein, we show that the sorption capacity can be substantially increased via the use of carbons with a higher specific capacitance. The highest gravimetric sorption capacity was measured with electrodes made from garlic-roots derived activated carbon valuing 273 mmol.kg-1 having a specific capacitance of 257 F.g-1. In addition, the overall adsorption rate and productivity were improved. Cycling the electrodes for over 100 h showed highly reproducible, reversible CO2 adsorption and desorption behavior. A preliminary technoeconomic and sensitivity analysis is provided to demonstrate the potential of SSA for commercial applications.