(Invited) Electrochemically Modulated Mitigation of Acid Gas Emissions

Abstract

The alarming rise in anthropogenic CO2 levels in the atmosphere due primarily to fossil fuel emissions is leading to significant changes in global climate patterns and increasing ocean acidities, with their severe negative impacts on the health of our planet. The mitigation of these acid gas emissions is a daunting task, both because of the scale of the problem and because of the economic ramifications associated with the capture of the greenhouse gases and their subsequent utilization or subsurface storage. The traditional means for CO2 capture and release generally rely on either chemical or physical interactions with sorbents with subsequent temperature or pressure changes to release the captured CO2 and regenerate the sorbent. The captured CO2 can then be compressed for injection and sequestration in subsurface geological formations or converted to useful products. These processes require significant energy integration which adds complexity and cost to the overall capture operation. Isothermal operations that obviate or significantly reduce the heat integration requirements in these processes could have significant advantages over the traditional methods. One such approach is to exploit electrochemical technologies for the capture and release of CO2, which can be operated isothermally, and can rely only on renewable energy resources, if desired.The general principles underlying electrochemically modulated acid gas separation processes will be outlined, with an emphasis on the thermodynamic and transport considerations required for their effective implementation in carbon capture. In particular, we will consider electrochemical technologies for the capture of CO2 that are suitable for both point-of-use gas emissions mitigation, and for removal from the atmosphere and ocean waters, where CO2 has been accumulating for decades. Examples include an indirect approach, in which an electrochemically released species (e.g., copper ions, protons) displaces the CO2 bound to a chemical sorbent via competitive complexation; the CO2 and the sorbents are regenerated when the species is re-captured in the cathode chamber of an electrochemical cell, leaving the sorbent free to be cycled back to the absorber. An alternative approach exploits the complexation of an electroactive moiety directly with the CO2 upon activation by electrochemical reduction, and releases the CO2 when it is re-oxidized on reversal of the applied cell voltage. In general, these electrochemically based technologies hold promise for tackling the climate change challenges that we, and future generations, must face.