The undisputed warming of the planet and increasing ocean acidification, with their strong implications for global climate and eco system changes, can be attributed to the increasing accumulation of anthropogenic CO2 in both the atmosphere and ocean waters. Strategies to mitigate these effects cannot rely simply on accelerated use of renewable energy resources to replace fossil fuels, but must include the capture of CO2 both at concentration from point sources, and at low concentrations from the ambient air or oceans, with subsequent subsurface sequestration or utilization. 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. Isothermal operations that obviate or significantly reduce the heat integration requirements in these processes could potentially have significant advantages over the traditional methods in terms of complexity, energetics and cost of the overall capture operation.
Electrochemically based technologies relying primarily on renewable energy resources for the capture and release of CO2 under isothermal conditions may prove to be a reliable approach for addressing the environmental crises facing the world. These approaches are suitable for both point-of-use gas emissions mitigation, and for removal of CO2 from the atmosphere and ocean waters, where it 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, with subsequent release of the CO2 when the agent is re-oxidized on reversal of the applied cell voltage. The thermodynamic and electrochemical principles underlying these processes will be discussed, with examples from both the direct and indirect approaches. In general, these electrochemically based technologies hold promise for tackling the climate change challenges that we, and future generations, must face.