Modeling and Performance Projections of a Dual-Purpose CO2 Capture and Energy Storage Device from Oceanwater

Abstract

Carbon dioxide (CO2) capture and removal technologies are critical to limit global warming to 2 °C in the next few decades. In addition to the atmosphere, the oceans are large carbon sinks and have to-date captured about 25% of all anthropogenically released carbon. Therefore, ocean water CO2 capture can complement Direct Air Capture (DAC) technologies. To harness this source of CO2, this talk proposes, models, and analyzes the performance implications of a reversible, aqueous electrochemical flow device, which uses hydrogen and redox salt looping to achieve pH shifting. The reversible nature of this device enables its use in both power production and consumption modes, enabling CO2 capture to be powered exclusively by variable sources of renewable electricity. To model the performance of the proposed energy storage and CO2 capture device, we developed an equivalent circuit model to predict the current-voltage performance of this device mediated by ferricyanide/ferrocyanide and H2. Performance predictions are modeled as a function of key transport and thermodynamic conditions, specifically, for different mass transport rates of gases and aqueous electrolytes and different extents of pH shift between acidification and basification steps. Estimations of device performance are developed at both laboratory-scale and industrially relevant current densities. Modeled electrochemical energy intensity values of the overall device operation are compared to current state-of-the-art electrochemical ocean CO2 capture technologies to show the approach’s potential. Overall energy intensities are compared to current state-of-the-art DAC technologies. Our results show the energy intensity for CO2 capture during the reversible process has the potential to be reduced compared to present day DAC systems, but is highly sensitive to parasitics, ohmic losses, and the extent of competing reactions. Additionally, projections of the device energy-time profile are demonstrated to show the diurnal energy storage potential, specifically with applications to solar energy. Energy storage capabilities in the proposed device provide additional benefits of powering this CO2 capture device with renewable electricity while providing flexibility to manage grid-scale electricity demand. Overall, a reversible, pH-shifting based oceanic CO2 capture device offers holistic benefits from designing CO2 capture to operate exclusively from renewable electricity.