Investigating electron transfer kinetics in redox flow batteries [article]

Leatham Landon-Lane, University Of Canterbury
2020
Vanadium Redox Flow Batteries can enable an increase in the fraction of renewable energy sources, such as solar and wind generation in electricity grids around the world. This in turn will help to reduce CO2 emissions and begin to combat global warming. Vanadium Redox Flow Batteries are a great choice for energy storage as they are non-flammable, with long lifecycles of 20 years or more. However, currently the capital cost is too high limiting their deployment. The cost of the vanadium
more » ... e vanadium electrolyte is dependent on the demand for vanadium on the open market, which is dominated by demand for hardened steel. In contrast, improving the performance of carbon felt electrodes will lead to an increase in power density of the cells, reducing the cell cost. Many treatments have been applied to carbon felts, with the aim of improving the inherent kinetics, surface area, wettability or conductivity. Typically, improvements in at least one area reported, however the source of improvements is not always assigned and often when it is the improvement is only qualitative. This is due to the complex and dis-ordered nature of the carbon felt electrodes which are typically used. In this work we have used single carbon fiber electrodes extracted from carbon felt samples, providing a defined cylindrical geometry and enabling quantative analysis of cyclic voltammetry and electrochemical impedance spectroscopy. Single fiber electrode results were then extended to measurements at carbon felt. Numerical simulation of the carbon felt electrode were carried out by approximating the carbon felt as an array of cylindrical electrodes, with a specific void distribution. The analysis of the experimental results highlighted the importance of the void size distribution and supported the finding from single fiber measurements, that there was a rate constant distribution within the felt for the Fe(CN)63− / Fe(CN)64− redox couple. Cyclic voltammetry of four different carbon fiber electrodes before and after thermal treatment at 450 oC for 1 hour, show [...]
doi:10.26021/10401 fatcat:gjukf5kbdvbc7eqpr5t2qv2fnq