The role of electrode orientation to enhance mass transport in redox flow batteries

Abstract

Mass transport plays a crucial role in the performance of redox flow batteries (RFBs). Generally, the electrodes used in RFBs are assemblies of randomly oriented carbon fibers (e.g. graphite felts, carbon papers). It has been shown that ordered arrangements exhibit enhanced mass transport performance (e.g. carbon cloths). Our investigations are focused on evaluating the role of the electrode orientation alone, on the mass transport with electrodes oriented parallel and perpendicular to the electrolyte flow direction. The electrodes employed were prepared with embroidery, and composed of Cu wires 80 µm in diameter. The space between wires was maintained at 1.1 mm during construction to enable complete electrolyte accessibility through the electrode, and the cell structure was designed to ensure uniform electrolyte velocity across the whole electrode surface area. The limiting currents were measured for both electrode orientations with linear sweep voltammetry. The results showed 18% greater mass transport coefficient for the perpendicular orientation as a consequence of greater accessibility of the reactants to the electrode surface. The findings provide insights for the optimization of electrode designs in mass-transport-limited reactors, such as RFBs. Keywords: Redox flow batteries, Mass transfer coefficient, Electrolyte velocity, Electrodes, Fiber orientation