Energy Harvesting from CO2 Emission Exploiting Ionic Liquid-Based Electrochemical Capacitor

Abstract

When two solutions with different compositions are mixed, the free mixing energy is released. This principle is exploited in salinity gradient power technologies like capacitive mixing (CapMix), where mixing occurs in a supercapacitor. Since this energy release holds true also for gases, research moves in the direction of harvesting energy from anthropic CO₂. To do so, it is proposed for the first time to exploit an ionic liquid (IL), both as an electrolyte and CO₂ absorbing medium in a CapMix cell. The mechanism consists in flowing a CO₂-rich gas stream, alternated to a N₂ stream, during the charging/discharging of two electrodes. The CO₂ strongly affects the electrode/IL interface and the IL physicochemical properties thereby converting the released mixing energy into electrical energy. Unlike water-based systems, where energy harvesting relies on electric double-layer expansion, we propose a new mechanism based on electrochemical potential variations during CO₂ capture/release, supported by molecular dynamics modeling. Key results include maximum voltage rise of 40 mV and energy and power densities of 40 μWh m⁻² and 0.8 mW m⁻². These findings clarify the mechanism behind the electrochemical phenomena occurring when CO₂ interacts with IL and open the way to a new generation of electrochemical systems to harvest energy from CO₂ emission.