ИСТИНА

The energy consumption is growing from year to year and we have to use it properly. Electrochemical sources optimization will let us reduce energy waste. We suggest using supercritical CO2 phase for polymer membranes modification for vanadium redox flow batteries (VRBs) applications. Vanadium redox flow batteries seems to be one of the most actual sources nowadays due to their high efficiency, simple construction, electrolyte cross‐contamination problem absence and output power and energy storage independence. The key component of the VRBs is ion‐exchange membrane that provides proton transport and prevents vanadium ions’ cross‐contamination. Membrane should be mechanically and chemically stable in aggressive electrolyte media as well. Currently, Nafion membranes are the most suitable ones for VRBs applications. It’s microphase‐separated structure allows to obtain high proton conductivity when PTFE backbone provides chemical stability. Though, high level of electrolytes cross‐contamination through Nafion and it’s extremely high cost leads to the further research in this field. In order to overcome the existing drawbacks we studied the techniques of membrane modifications via supercritical fluid for vanadium redox flow batteries (VRFBs) applications. Supercritical fluid, such as scCO2, seems to be perfect phase for homogenous membrane modification due to the absence of capillary effects [1]. In our work, we suggested using scCO2 for uniform inorganic phase injection inside polymer matrix. With the aim of proton conductivity increase and vanadium ions’ transport suppression we embedded tungsten oxides nanoparticles inside hydrophilic Nafion channels. Tungsten oxides are known to be able to form tungstic acid [2]. Moreover, difference of physical and Stockes radius of protons (H3O+ ) and vanadium ions (VO2+) lets one make membrane selective: tungsten oxides Fig. 1. The XRD patterns of pristine Nafion (red line) and Nafion with injected tungsten oxides (gray line). 165 particles fill Nafion channels so their effective diameter reduces, preventing vanadium ions’ transport. The membranes were exposed with tungsten hexacarbonyl precursor at 120 °C in scCO2 media in the oxygen presence. The exposition led to uniform tungsten oxides particles formation inside Nafion channels. According to the XRD results, WO3͘ · ଵ ଷ H2O and W3O8 phases were found in polymer matrix (Fig. 1). Inorganic phase concentration was varied by the means of oxides particles dissolvent in hydrogen peroxide. With the tungsten oxides concentration increase a non‐monotonic behavior of proton conductivity is observed with maximum at 2.1 wt. % (Fig. 2). It can be explained by two opposing mechanisms: tungstic acid presence leads to conductivity increase, when too high particle amount leads to mechanical blocking of the channels. For the same reason the vanadium permeability is suppressed with the inorganic phase concentration increase. Summing up, using scCO2 for membrane modification is an effective and profitable method, the potential of which has not been fully revealed yet.