State-of-the-art all-vanadium redox flow batteries employ porous carbonaceous materials as electrodes. The battery cells possess non-scalable fixed electrodes inserted into a cell stack. In contrast, a conductive particle network dispersed in the electrolyte, known as slurry electrode, may be beneficial for a scalable redox flow battery. In this work, slurry electrodes are successfully introduced to an all-vanadium redox flow battery. Activated carbon and graphite powder particles are dispersed up to 20 wt.% in the vanadium electrolyte and charge-discharge behavior is inspected via polarization studies. Graphite powder slurry is superior over activated carbon with a polarization behavior closer to the standard graphite felt electrodes.3D-printed conductive static mixers introduced to the slurry channel im-prove the charge transfer via intensified slurry mixing and increased surface area. Consequently, a significant increase in the coulombic efficiency up to 80 % and energy efficiency up to 50 % is obtained. Our results show that slurry electrodes supported by conductive static mixers can be competitive to state-of-the-art electrodes yielding an additional degree of freedom in battery design. Research into carbon properties (particle size, internal surface area, pore size distribution) tailored to the electrolyte system and optimization of the mixer geometry may yield even better battery properties.

We studied the half-cell performance of a slurry-based vanadium redox flow battery via the polarization and electrochemical impedance spectroscopy methods. First, the conductive static mixers are examined and lower ohmic and diffusion resistances are shown. Further analyses of the slurry electrodes for the catholyte (VO 2 + À VO 2 + ) and anolyte (V 3 + À V 2 + ) are presented for the graphite powder slurry containing up to 15.0 wt.% particle content. Overall, the anolyte persists as the more resistive half-cell, while ohmic and diffusion-related limitations are the dominating resistances for both electrolytes. The battery is further improved by the addition of Ketjen black nanoparticles, which results in lower cell resistances. The best results are achieved when 0.5 wt.% Ketjen black nanoparticles are dispersed with graphite powder since the addition of nanoparticles reduces ohmic, charge transfer and mass diffusion resistances by improving particle-particle dynamics. The results prove the importance of understanding resistances in a slurry electrode system.

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New electrode geometries with high porosities are of great interest for electrochemical processes. By using additive manufacturing design, the limitations of conventional production processes can be overcome. The presented laserless additive manufacturing method allows us to print any geometrical shape using metal and ceramic pastes. Here, the paste compounds were 70 vol% nanocellulose and 30 vol% metal/ceramic powder. Two different electrode geometries were printed, the disc and the gyroid. Furthermore, two different geometries of membrane electrode assemblies (MEAs) were printed: a flat and a tubular MEA. Following printing, the green samples were sintered. Afterwards, the disc electrode and flat membrane electrode assembly were coated with IrO2 (anode) and Pt (cathode) catalysts. The coated samples were assembled into a polymeric MEA water electrolyzer (pMEA) and into a ceramic MEA water electrolyzer (cMEA) to evaluate their potentials.