Impact of carbonaceous particles concentration in a nanofluidic electrolyte for vanadium redox flow batteries

Carbon based vanadium nanofluids with different carbon weight percentages (0, 0.02, 0.04 and 0.08 wt %) have been prepared to be used as electrolyte in a redox flow battery. Physical-chemical characterization of the carbon nanoparticle powders and the prepared nanofluids is carried out. All prepared carbon nanofluids show a stable behaviour, making them perfect candidates to be used as electrolyte in a redox flow battery. Besides, an electrochemical characterization in a bench scale redox flow battery is performed. Charge and discharge cycles are carried out at different current densities (30, 40, 50 and 60 mA cm−2). The results show that the addition of nanocarbon particles into the commercial vanadium electrolyte increases the active surface area where the redox reactions can take place, decreasing the ohmic resistances. The collisions among the current collectors and electrodes with the nanocarbon particles favour the contact between both plates due to the formation of a conducting network of electrons, increasing the performance of the battery. Nanofluids with a 0.04 wt% of carbon nanoparticles attained higher capacities and efficiencies at higher current densities (60 mA cm−2) than the commercial vanadium electrolyte without nanocarbon particles.