Abstract:

We demonstrate the use of fluorescence microscopy as a tool for mapping the spatial distribution of fluid flow and electrochemical reactions in an operating aqueous quinone flow cell. 9,10-anthraquinone-2,7-disulfonic acid (AQDS) is a reversibly redox active molecule with a reduced form (H2AQDS) that fluoresces when excited by UV light. Visualization of AQDS/H2AQDS within commercial porous carbon electrode papers enables a direct comparison of their performance. In particular, this technique illuminates surprisingly large-scale heterogeneous fluid flow profiles present in several carbon papers, leaving substantial areas of the electrode mass-transport limited. In others, more homogeneous flow distribution is observed, but limitations such as low electronic conductivity and limited accessible electrode surface area limit the performance. This work provides insights into improving structural properties of porous electrodes for high-power density electrochemical flow cells.