Quantifying Losses at the Positive and Negative Electrodes of a VRFB

Open Access
Author:
Edwards, Forest
Area of Honors:
Energy Engineering
Degree:
Bachelor of Architectural Engineering
Document Type:
Thesis
Thesis Supervisors:
  • Derek M Hall, Thesis Supervisor
  • Sarma V Pisupati, Honors Advisor
Keywords:
  • vanadium redox flow battery
  • battery
  • vanadium
  • voltage efficiency
  • energy engineering
Abstract:
Vanadium redox flow batteries are still in their infancy as a technology, and as such there are still many gaps in the knowledge of their mechanics. An important quality that is still unclear is the limiting electrode, particularly whether it is the negative or the positive electrode which generated more losses and therefore reduced the voltage efficiency of the battery the most. By quantifying these losses the role of those attempting to reduce them in the future is made much simpler as they will not need to identify where they are, just how to improve them (not that this is a simple task by any means). The central hypothesis of this thesis is that the overpotential and losses of the positive electrode due to its unfavorable kinetics are the largest contributor to potential losses at high voltage efficiencies before IR drop dominates the losses. This thesis quantified the loss contributions by source as a function of voltage efficiency and cell current density to confirm this hypothesis. The potential losses at the positive electrode were found to dominate the losses at the negative electrode at low current densities. This was found by a combined linearized Butler-Volmer and Tafel model, which showed that even at its highest points at a current density of 1.6E-4 A/cm2, the losses at the negative electrode did not exceed 22% of total losses. The losses of the positive electrode were found to dominate the losses of the negative electrode at all current densities, and this trend continued after Ohmic losses surpassed the combined overpotentials at the positive and negative electrode.