Dispersion stability of flow-electrodes for enhanced flow-electrode capacitive mixing performance: Requirements for conductive additives

Flow-electrode capacitive mixing (F-CapMix) is a promising technology for salinity-gradient power generation that allows continuous energy harvesting using carbon-based flow-electrodes. However, its practical implementation is hindered by low power density, primarily arising from inefficient ion and electron transport within the flow-electrode. This study investigates the role of carbon nanofibers (CNFs) as conductive additives for enhancing the F-CapMix performance. Three types of CNFs with distinct morphologies and electrical conductivities are incorporated into flow-electrodes, and their rheological and electrochemical properties are systematically evaluated. Among them, GNF-A, with the lowest electrical conductivity, demonstrates superior electrochemical performance of F-CapMix owing to its minimal fiber entanglement, and high dispersion stability in the flow-electrode. GNF-A enhances the connectivity between activated carbon particles with an established stable elastic network and facilitates efficient ion and electron transport. In contrast, GNF-L, possessing the highest conductivity, shows limited performance enhancement owing to poor dispersion behavior. These findings highlight that dispersion stability and morphological compatibility with the electrode matrix are more crucial than electrical conductivity in determining the effectiveness of conductive additives. This study offers practical design principles for the development of high-performance flow-electrodes in F-CapMix systems.