Study on Particle Sizes for Graphite/Polyphenylene Sulfide Composite Bipolar Plates for Vanadium Redox Flow Battery

All vanadium redox flow battery (VRB) is a promising candidate for large scale storage of electrical energy. This device can be used for storing intermittent power supply from solar cells and wind turbines, and also offers economically viable backup storage system for large energy electrical grids. Bipolar plates of VRB are designed to distribute the positive and negative electrolytes, separate the individual cells and carry current away from the cells. The bipolar plates are prone to suffer from corrosion in concentrated acid environment. Therefore, bipolar plates should have proper characteristics followed by high oxygen and hydrogen overvoltage, good chemical stability, electrical and thermal conductivity.

The corrosion performance of composite bipolar plates with different graphite particle sizes and polyphenylene sulfide was investigated. The potentiodynamic tests, potentiostatic tests, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were conducted for evaluating these composite bipolar plates. The results indicated that the composite bipolar plates with 105μm graphite particle size had the lowest O/C ratio which demonstrated that the composite bipolar plate had good corrosion resistant performance.

 The composite bipolar plates with 105μm graphite particle size were fitted to a single cell VRB. The 80 charge-discharge cycles were conducted at higher current density of 120mA/cm2. The cell showed good charge-discharge operation and maintained a high Coulomb efficiency of about 95% with the maximum energy efficiency of about 85%.