Study Of Positive Electrolyte For All-vanadium Redox Flow Battery

In this paper, to improve the electrochemical performances and thermal stability of positive electrolyte for all-vandium redox flow battery (VRFB), inositol and phytic acid as additives and CH3SO3H and H2SO4mixed acid as the supporting electrolyte were studied. The main points can be summarized as following.Inositol and phytic acid have been employed as organic additives of the positive electrolyte for all-vandium redox flow battery (VRFB). The effects of additives on electrolyte were studied by cyclic voltammetry (CV), steady polarization curve, electrochemical impedance spectroscopy (EIS), UV-visible spectroscopy (UV) and scanning electron microscope (SEM). The results showed that thermal stability and electrochemical activity of the positive electrolyte were improved with adding inositol or phytic acid, this may be interpreted that the additives facilitated dispersion of the hydrated form of V(V) ions for they are able to absorb on the surface of the nuclei by-OH and=O groups. Besides, the additives effectively reduced the viscosity of the electrolyte and increased available-OH groups providing active sites for electron transfer. The capacity of the VRFB employing the electrolyte with phytic acid decreased significantly, probably owning to the formation of sediments on the positive graphite felt. The VRFB employing the vanadium electrolyte with inositol exhibited excellent charge-discharge behavior with high average energy efficiency (81.5%) at a current density of30mA-cm-2.All kind percentage of CH3SO3H and H2SO4mixed acid solution (MAS sample) were used as the supporting electrolyte for VRFB. The CV and EIS results revealed that the MAS sample had a higher reversible redox reaction than pristine sample, and the optimal proportion of MSA is50%. The vanadium redox cell with the electrolyte using1.5mol/L CH3SO3H and1.5mol/L H2SO4as supporting electrolyte exhibited the best electrochemical performance (the energy efficiency85.2%). At120 mA·cm-2, VRFB with MAS sample exhibited the higher discharge capacity in comparison of pristine sample. The improved thermal stability and electrochemical activity could be attributed to the change of vanadium species.