Effects of methanesulfonic acid on electrolyte for vanadium redox flow batteries

Abstract Methanesulfonic acid (MSA) is investigated as an additive for improving the thermal stability and electrochemical property of the vanadium redox flow battery (VRFB) electrolyte. The effect of MSA on the thermal stability of the electrolyte is estimated by a storage test, inductively coupled plasma mass spectrometry, and ultraviolet–visible spectrometry. Thermal stability tests show that MSA delays the formation of precipitates. The precipitates formed from the electrolyte are analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The precipitates gained from the V(II) electrolyte at −5 °C and the V(V) electrolyte at 40 °C have different physicochemical properties. The influence of MSA on the electrochemical property is examined by cyclic voltammetry, linear polarization, and electrochemical impedance spectroscopy. According to the electrochemical analysis, MSA enhances the diffusion of the V(III) and V(IV) ions and the redox reaction rate of the V ions. Additionally, nuclear magnetic resonance analysis is performed to understand the positive effect of MSA on the electrolyte. A VRFB full cell employing the electrolyte with MSA shows enhanced energy efficiency as well as high energy density by improving electrolyte utilization.