3D-printed conductive static mixers enable all-vanadium redox flow battery using slurry electrodes

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 improve the charge transfer via intensified slurry mixing and increased surface area. Consequently, a significant increase in the coulombic efficiency up to 95% and energy efficiency up to 65% 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

Microtubes made of carbon nanotubes

Microtubes made of multi-walled carbon nanotubes were prepared via infiltration of CNT-suspension through a microfiltration hollow fiber membrane. Shrinking of the entangled CNT network during the drying allows withdrawal of CNT-microtubes from the hollow fiber. Currently, microtubes have a length of ∼50 cm, outer diameter of ∼1.7 mm and scalable inner diameter by varying the infiltration time resulting in wall thicknesses of 130-320 μm. The BET surface area is 200 m2/g with a porosity of 48-67% and an electrical conductivity ∼20 S/cm. We propose to use such novel CNT-microtubes for the fabrication of tubular electrochemical cells and membrane filtration processes.This research was funded by the German Federal Ministry of Education and Research (BMBF) under the project “Tubulair±”. Prof. Matthias Wessling appreciates the financial support of the Alexander von Humboldt Foundation.Peer reviewe

Single module flow-electrode capacitive deionization for continuous water desalination

The search for novel desalination technologies has recently led to the introduction of flow-electrodes to capacitive deionization (CDI) processes, named as flow-electrode capacitive deionization (FCDI). Unlike classical CDI, which is a discontinuous or semi-continuous process due to the need for regeneration of the electrodes within the same module, flow-electrodes offer new design opportunities which enable fully continuous desalination processes as well as easily scalable systems. Here, we describe a novel system for the continuous desalination of water based on FCDI using a single flow-electrode and a single module. The flow-electrode is based on activated carbon powder suspended in water. During continuous operation of the system, a desalination rate of a 1 g/L NaCl solution of up to 70% is achieved at water recoveries of up to 80%. Additionally we report very good current efficiencies: in case of 80% water recovery, the current efficiency is 0.93. The single flow-electrode single module process might reduce energy and investment costs and lower the threshold to a large scale implementation. Keywords: Capacitive deionization, Water desalination, Flow electrodes, Electrosorption, Suspension electrode

Proton-exchange membranes based on sulfonated poly(ether ether ketone)/polyaniline blends for all- and air-vanadium redox flow battery applications

Publisher Copyright: © 2015 Elsevier Ltd.Thin and mechanically stable proton-exchange membranes with high V(IV) barrier properties and good proton conductivity have been fabricated by polymer blending of sulfonated poly(ether ether ketone) with polyaniline. V(IV) diffusion coefficient of blended membranes in a wt. ratio of 80/20 was 2.6 and 6 times lower than for pure sulfonated poly(ether ether ketone) and Nafion 112 membrane, respectively. This behaviour is assumed to be caused by a densified polymer matrix given by acid/base interactions between the two polymers. Blended membranes in a wt. ratio of 80/20 had a good proton conductivity of 54.15mScm-1 and ion exchange capacity of 1.44mmolg-1. The membranes were also characterized in all-vanadium redox flow battery, where only slightly higher efficiencies were achieved than for pure polymer. Slow PANI degradation determines a decrease in membrane performance, reaching values close to the starting polymer (SPEEK-E600). Therefore, the application of blended membranes in the all-vanadium redox flow battery is not advantageous. However, the improved barrier properties are likely to be beneficial for their application in vanadium/air-redox flow battery in order to reduce oxygen crossover. In the latter, no V(V) ions can oxidize the blend polymer.This research was funded by the German Federal Ministry of Education and Research (BMBF) under the project Tubulair±. Prof. Matthias Wessling appreciates the financial support of the Alexander von Humboldt Foundation .Peer reviewe

Tubular carbon nanotube-based gas diffusion electrode removes persistent organic pollutants by a cyclic adsorption – Electro-Fenton process

Publisher Copyright: © 2016 Elsevier B.V.We report a novel tubular electrochemical cell which is operated in a cyclic adsorption - electro-Fenton process and by this means overcomes the drawbacks of the traditional electro-Fenton process. A microtube made only of multi-walled carbon nanotubes (MWCNT) functions as a gas diffusion electrode (GDE) and highly porous adsorber. In the process, the pollutants were first removed electroless from the wastewater by adsorption on the MWCNT-GDE. Subsequently, the pollutants are electrochemically degraded in a defined volume of electrolyte solution using the electro-Fenton process. Oxygen was supplied into the lumen of the saturated microtubular GDE which was surrounded by a cylindrical anode made of Ti-felt coated with Pt/IrO2 catalysts. For the proof of concept the model pollutant Acid Red 14 (AR14), an azo dye, was used. The decomposition of AR14 was studied at different applied current densities and initial concentrations of ferrous iron in the electrolyte solution. At optimal conditions, complete regeneration of the adsorption capacity of the MWCNT-GDE, complete decolorization and TOC and COD removal rates of 50% and 70% were achieved, respectively. The MWCNT-GDE is regenerated and again available for adsorption. This approach allows water treatment independent of its composition, thus does not require any addition of chemicals to the wastewater.Matthias Wessling appreciates the financial support of the Alexander von Humboldt Foundation .Peer reviewe