Comparative Investigation of Polyphenylene Sulfide Polymer-Graphite Bipolar Plates for Fuel Cell Application

Abstract

Bipolar plates (BPPs) are one of the key components of the polymer electrolyte membrane fuel cell (PEM FC) which play an important role in the development of fuel cell application. They should fulfil many functions in a fuel cell stack such as feeding H2 and O2 gases through the flow field upon operation, heat transfer, physical separation of individual fuel cells in series, collection and transport of electrons from anode to cathode of adjacent cells [1]. Among the BPPs used in PEM FC the polyphenylene sulfide (PPS) polymer-graphite BPP has a good electrical conductivity, lower cost, higher flexibility and chemical stability, in comparison to metallic and graphite plates. However, some challenges such as higher thickness and weight in comparison to metallic bipolar plates are limiting their use in automotive application [1]. In addition, it was reported that corrosion of carbon is taking place under operation conditions of fuel cells [2]. Therefore, in this work two compression molded commercial polyphenylene sulfide (PPS) polymer-graphite composite bipolar plates BPP-20 and BPP-15 from two different manufacturers with amount of PPS binder equal to 20 and 15 %, respectively, were employed for an analytical comparative investigation using physical and electrochemical analysis. Chemical stability of BPPs was investigated after storage in phosphoric acid. Corrosion resistance and electrochemical aging of the BPPs were studied by using linear sweep voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy in phosphoric acid. In order to characterize the difference in physical properties water contact angle measurement and through-plane electrical conductivity experiments were performed. The morphology of the BPPs surfaces was determined by scanning electron and confocal microscopy. The chemical composition was investigated by X-ray diffraction and energy dispersive X-ray spectroscopy, respectively. Comparison of BPPs revealed that the surface roughness and electrical conductivity is lower while acid uptake and hydrophilicity is higher for BPP with higher amount of PPS. Moreover, there was a trend of reduced corrosion rate for BPP with increased PPS content. These properties could be explained based on structure and electrical characteristics of the materials. [1] S. S. Araya, F. Zhou, V. Liso, S. L. Sahlin, J. R. Vang, S. Thomas, X. Gao, C. Jeppesen, S. K. Kær, International Journal of Hydrogen Energy 2016, 41, 21310-21344. [2] T. Engl, L. Gubler, T. J. Schmidt, Journal of the Electrochemical Society 2015, 162, F291-F297. Figure 1