Electrochemical Flow Systems for Stationary Energy Storage and CO₂ Capture

Organic-based aqueous flow batteries have been developed with the goal of rapid scaling to cost-effectively store electrical energy from intermittent renewable sources for use when the wind isn’t blowing and the sun isn’t shining. Redox-active organic molecules in aqueous solution can reversibly bind CO₂ directly in one redox state and release it in the other. The same molecules can swing the pH by undergoing proton-coupled electron transfer, thereby enabling CO₂ capture by hydroxide. Recent progress in the development of active materials and cell designs will be reported.<br/>Modest areal power densities in both of these applications, caused in part by mass transport limitations within the cell stack, limit system performance. A detailed understanding of mass transport and electrochemical activity within the porous electrode would benefit all electrochemical flow systems. We use <i>operando</i> fluorescence microscopy to image the fluid flow velocity field and molecular concentration fields using fluorescent tracer particles and redox-active organic molecules respectively. The molecular fluorescence signal is converted to a local measure of the state of charge with sub-pore-scale resolution. We are using this quantitative electrochemical fluorescence microscopy technique to gain insight into the influence of the electrode architecture on electrochemical-flow processes and, ultimately, to guide the development of high-performance electrodes for redox flow based electrochemical systems