A Vanadium Redox Flow Process for Carbon Capture and Energy Storage

Abstract

Climate change mitigation by decreasing worldwide CO2 emissions is an urgent and demanding challenge that requires innovative technical solutions. This work, inspired by vanadium redox flow batteries (VRFB), introduces an integrated electrochemical process for carbon capture and energy storage. It utilizes established vanadium and ferricyanide redox couples for pH modulation for CO2 desorption and absorbent regeneration. The developed process consumes electricity during the daytime—when renewable electricity is available—to desorb CO2 and charge the cell, and it can regenerate the absorbent for further CO2 absorption while releasing electricity to the grid during nighttime when solar power is unavailable. This research explores the process fundamentals and scalability potential, through an extensive study of the system's thermodynamics, transport phenomena, kinetics, and bench-scale operations. Cyclic voltammetry (CV) was utilized to study the thermodynamics of the process, mapping the redox profiles to identify ideal potential windows for operation. The CV results pinpointed a 0.3 V Nernstian overpotential as the thermodynamic minimum required for cell operation. Additionally, polarization studies were conducted to select the practical operating potential, identifying 0.5 V as optimal for the CO2 desorption cycle to provide sufficient polarity to overcome activation barriers in addition to the Nernstian potential. Mass transfer analysis balanced conductivity and desorption efficiency, with a 1:1 ratio identified as optimal for redox-active species and background electrolyte concentration. To further enhance the kinetics of the redox reactions, plasma treatment of electrode surfaces was implemented, resulting in a 43% decrease in charge transfer resistance, as measured by electrochemical impedance spectroscopy (EIS) analysis. Finally, a bench-scale operation of the system demonstrated an energy consumption of 54 kJ/mol CO2, which is competitive with other electrochemical carbon capture technologies. Besides its energy competitiveness, the process offers multiple additional advantages, including the elimination of precious metal electrodes, oxygen insensitivity in flue gas, scalability inspired by VRFB technology, and the unique ability to function as a battery during the absorbent regeneration process, enabling efficient day-night operation.