## 3 Results  
### The Interaction of Electrolyte Preparation and Discharging Performance  
Electrolytes mainly store the active redox species carrying electrical energy, so physical-chemical properties--solubility, stability, ionic conductivity, and viscosity--of prepared solutions signify critical factors for suitable functioning. The vanadium electrolytes are mostly gained from VOSO\({}_{4}\) or V\({}_{2}\)O\({}_{5}\)[34]. Nonetheless, V\({}_{2}\)O\({}_{5}\) naturally has very low solubility, resulting in a difficult-to-prepare electrolyte solution with a high vanadium concentration directly. This rational restriction leads to efforts to prepare solutions from other vanadium compounds such as V\({}_{2}\)O\({}_{3}\) and VCl\({}_{3}\)[35], but their expensive cost, low solubility, and low stability limit their applications exclusively for large-scale systems. Preparing electrolytes using vanadyl sulfate (VOSO\({}_{4}\)) as an initial reactant creates VO\({}^{2+}\), which is responsible for producing V\({}^{2+}\) and VO\({}_{2}\)\({}^{+}\) representing the state of charge (SOC) of 100% [35]. This implies that the reaction can be readily applied for a discharging step. This preparation method is suitable for refueling vanadium electrolytes in an electric vehicle tank. However, it is necessary to be concerned about low electrolyte solubility and electrolyte susceptibility oxidation to the air of the species V\({}^{2+}\) cause the low energy density of VRFB [12]. In terms of utilizing vanadium pentoxide (V\({}_{2}\)O\({}_{5}\)) as the initial reactant for the electrolyte preparation, dissolving vanadium pentoxide in sulfuric acid generates V\({}^{3.5+}\), which is the combination of V\({}^{3+}\) and VO\({}^{2+}\) electrolytes corresponding to a SOC of 0% [19], assuming that the VRFB must be charged before use. This pathway can be applied for EV charging station load, agriculture, and telecommunications integrated with solar cells and/or wind turbines as primary energy resources. In this study, electrolytic dissolution was used to begin the electrolyte production process utilizing VO\({}^{2+}\) as a source [35]. Since water is a naturally occurring solvent for electrolytes and is a highly polar solvent with the ability to dissolve ionic salts, using water as a solvent for electrolyte preparation is typically considered. That is due to meaningful differences in the electronegativity of hydrogen and oxygen atoms. Both cation and anion solutes excellently interact with water molecules, bringing about an extended solvation structure that theoretically corresponds to ion hydration [36]. Reactants for preparing electrolytes consist of active species and supporting electrolytes. Supporting electrolytes assist in increasing energy storage and ionic conductivity. As mentioned in the previous part, sulfuric acid has been extensively used as a supporting electrolyte to provide rational solubility (1.5-1.6 M). Note that VOSO\({}_{4}\) is adopted as a starting reagent since it possesses higher solubility in an aqueous H\({}_{2}\)SO\({}_{4}\) solution that is more than 10 times higher than that of V\({}_{2}\)O\({}_{5}\)[37]. In our work, the electrolyte preparation was begun from VOSO\({}_{4}\) in both half-cells, but the reservoir of the cathode side contained twice as much electrolyte solution as the reservoir of the anode side did. A logical prerequisite for imposing the electrolyte volume of the cathode and anode sides is the stoichiometry of the redox reaction occurring in a VRFB cell. One electron is lost during VO\({}^{2+}\) transformations into VO\({}_{2}\)\({}^{+}\) during oxidation, while two electrons are accepted during the reduction when VO\({}^{2+}\) is transformed into V\({}^{2+}\). That indicates that the VO\({}_{2}\)\({}^{+}\):V\({}^{2+}\) ratio is equivalent to 2:1, so in order to establish stoichiometry, the catholyte must be present in greater amounts than the analyte [32,33].