Evaluation of precipitation inhibitors for supersaturated vanadyl electrolytes for the vanadium redox battery

As part of a project aimed at increasing the energy density of the vanadium redox battery for mobile applications, a number of additives was evaluated as precipitation inhibitors to enhance the stability of supersaturated vanadyl electrolytes in H2SO4. While the saturation solubility of vanadyl sulfate in 3 M H2SO4 is less than 2 M/L at 10 degrees C, 4 M supersaturated vanadyl sulfate solutions could readily be prepared. A blank solution of 4 M vanadyl sulfate in 3 M H2SO4 began to precipitate after 22 days at 4 degrees C, reaching an equilibrium concentration of 1.43 M after 80 days. In the presence of 5 wt % K2SO4 or 3 wt % sodium hexametaphosphate, however, there was no sign of precipitation after 80 days at 4 degrees C. (C) 1999 The Electrochemical Society. S1099-0062(98)08-009-2. All rights reserved.