Enhancement in vanadium redox flow battery performance using reduced graphene oxide nanofluid electrolyte

Low energy storage performance of aqueous flow batteries is the main limitation in commercialization and worldwide implementation. The effect of nanofluids on the electrochemical behaviour of electrolytes to alleviate this problem has been rarely studied in contrast with the extensive heat-transfer-related literature on nanofluids from the field of thermal science. Therefore, this study aims to experimentally investigate the long-term effect of using reduced graphene oxide (rGO) nanofluidic electrolyte on vanadium redox flow battery performance, placing it amongst the very few studies on the effectiveness of nanofluids in flow batteries. Scanning Electron Microscopy (SEM), EDS elemental mapping, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) characterizations reveal changes in morphology, structural and elemental properties of the carbon felt electrodes due to the presence of suspended nano catalysts in the electrolyte. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) exhibited significant improvements of 36 % and 26 % in oxidation/reduction peaks, ~ 95 % of reduction in charge transfer resistance, and enhanced redox reactions reversibility of the optimum concentration of nanofluidic electrolyte (0.1 wt%). Moreover, active surface area of the electrodes were determined to be increased by ~130 % and ~ 135 % for positive and negative 1.0 wt% nanofluid-affected electrode samples compared to pure electrolyte-affected electrode. In addition, considering the optimum nanoparticle concentration of 0.1 wt%, charge, and discharge capacities of the flow battery outperformed where pure electrolyte was applied in different current densities. These enhancements show considerable increase in energy storage of the VRFB. Furthermore, energy efficiency and voltage efficiency of the flow cell were observed to be increased respectively by 15 % to 24 % and 8 % to ~21 % for the current densities from 25 to 150 mAcm−2 when the optimum concentration of nanoparticles was applied. This study gives new insight into the rarely studied applicability of nanofluids in vanadium flow batteries. •Stable enhancement in VRFB performance has been achieved.•rGO nanofluid electrolyte has been utilized as anolyte and catholyte in VRFB.•Comparatively high charge and discharge capacities were reported in high current densities.•Lower ohmic resistance and polarization effect were reported in 0.1 wt% nanofluid electrolyte VRFB.