Design of a Vanadium Redox Flow Battery

Abstract

In the past couple of centuries rapid industrialization and depletion of fossil fuels has increased the demand for renewable energy. Renewable energy is intermittent, e.g. solar energy is only available during the day. This prompts the need for efficient energy storage. Vanadium Redox Flow Batteries (VRFBs) provide a viable method to store energy. VRFBs store electrical energy by converting it to chemical energy via an oxidation-reduction reaction: Positive electrode: VO\(^{2+}\) + H\(_{2}\)O → VO\(_{2}\)+ + 2H\(^{+}\) + e\(^{–}\) Negative electrode: V\(^{3+}\) + e\(^{–}\) → V\(^{2+}\) Redox flow batteries pump unreacted fluid through a cell, storing energy via this reaction. The positive and negative electrodes are separated by a Nafion membrane, which only allows transport of hydrogen ions. The reaction will occur near carbon felt, which will act as a means for electron transport (current collector). In a flow-through design, the fluid is forced to flow through the carbon felt current collector, as opposed to flowing past a current collector. This allows all of the fluid to come in contact with the felt, hopefully providing a higher rate of reaction. In a cell where the fluid flows past a current collector, some of the fluid would not come in contact with the current, thus impeding the reaction. The membrane used was Nafion 115. Impurities were removed by boiling for an hour in 3% hydrogen peroxide, an hour in deionized water, an hour in 0.5M H2SO4, then an hour in deionized water. The pump used to provide flow was a Masterflex L/S Peristaltic Tubing Pump. Electrolyte was pumped continuously at 50 mL/min. Raw building materials used to fabricate the cells were purchased from McMaster Carr. These included: LDPE, HDPE, Stainless Steel, Corrosion-Resistant Nickel, and Corrosion Resistant Viton Fluoroelastomer Rubber. The carbon felt used as the electrode was purchased from CeraMaterials. Simple test schedules were run and recorded using Arbin Instruments’ MITS Pro software. The electrolyte was charged with a constant voltage of 1.7V, because this voltage is high enough to drive the oxidation-reduction reaction, while not high enough to drive the electrolysis of water. Then a load was applied allowing the cell to discharge. We were not able to achieve conclusive results. When testing the fuel cell, the charging section of the schedule would progress smoothly, but when the discharge began the system encountered an error. We cannot be certain that charging occurred. Even though we were unsuccessful in testing, we were successful in designing a leak free fuel cell. Given more time, we would try to investigate the reason why testing does not perform as expected.