The Vanadium Redox Flow Battery - Electrochemical Impedance Characterization

Joana Dias Fonseca

Key information

Authors:

Supervisors:

Alda Maria Pereira Simões (Alda Maria Pereira Simões); Rui Pedro da Costa Neto (Rui Pedro da Costa Neto (Rui Costa Neto))

Published in

01/28/2021

Abstract

With the increasing use of intermittent renewable energy sources, such as solar and wind energy, electricity storage systems such as redox flow batteries have been the target of growing interest. In this work, the electrochemical characterization of a Vanadium Redox Flow Cell (25 cm2) was performed. Polarization curves were taken where current densities achieved 11 mA/cm2 and 92 mA/cm2 for an electrolyte with vanadium concentration of 0.125 M and 1.21 M, respectively. Electrochemical Impedance Spectroscopy (EIS) measurements were made for different experimental conditions to study the response of the cell. The cell's ohmic resistance for standard experimental set up and a vanadium concentration of 0.125 M was found to be 3.9 ohm cm2 and 97% of it accounts for the membrane. The faradaic resistance varied with the cell's State of Charge (SOC) and ranged from 3.8 to 13 ohm cm2, its lowest value at 30-70% SOC. The charge-transfer resistance increases 15.2 times with the removal of the carbon felts, and mass transport variations were also observed. The economic assessment of a VRFB installation in a "Recheio" Supermarket in Tavira was performed and the project resulted in a positive Net Present Value (NPV) of 43 247 € after 20 years.