Pathan, TS; (2017) Development and Characterisation of Functionally Coated Steel as a Bipolar Plate Material for Polymer Electrolyte Membrane Fuel Cells. Doctoral thesis , UCL (University College London).

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Abstract

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) produce electricity with minimum environmental impact. The major hurdles in commercialisation of PEMFCs are the high commissioning and operation costs and the durability of the cell. A bipolar plate (BPP) is a key weight and cost determining component in PEMFC that undertakes significant performance-determining functions in the cell. Currently, stainless steel is used as a BPP in large number of commercial PEMFCs; however, corrosion within the harsh fuel cell operating environment remains a major concern. Further, the formation of passivation layers reduces the electrical conductivity and the overall performance. The aim of the study is to develop and characterise functional coatings for different grades of steel, including mild steel for BPP applications. Compared to stainless steel, mild steel is low cost, but has poor corrosion properties, thereby requiring a coating. Mild steel with a proprietary coating was analysed with improved contact resistance and corrosion resistance under simulated fuel cell environment. Potentiodynamic, potentiostatic and accelerated corrosion tests have been used to analyse the coated mild steel and the results are compared with commercial SS 316L. In situ fuel cell results are reported using SS 316L and compared with graphite to demonstrate the significance of passive layer. Graphene was deposited on different grades of steel owing to its excellent chemical and mechanical properties, high durability, excellent corrosion resistance and high electrical conductivity. This was achieved using chemical vapor deposition; with improved contact resistance and electrophoretic deposition; with improved corrosion resistance. Finally, a novel method of corrosion analysis is presented using 3D x-ray computed tomography in an attempt to understand the sub-surface propagation of corrosion in coated samples. This study results in better understanding of the corrosion phenomena in PEMFC environment and also provides coating options for reducing the cost of PEMFC operation whilst improving overall output.

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