Multi-Layer Thin Film Coatings on Bipolar Metal Plates for PEMFC

Abstract

The proton exchange membrane fuel cell (PEMFC) offers the potential for an efficient, and reliable power source for vehicles. The bipolar plates are a key component in the stack providing mechanical support, supplying reactant gases to both anode and cathode, removing the reaction products, and providing electrical and thermal conductivity. [1] Bipolar plate materials are broadly divided into metallic and carbon-based materials. Carbon-based plate materials do well mechanically; still fabrication is difficult and costly. As a result, metallic bipolar plates are becoming increasingly popular.[2] Metal bipolar plates have all the necessary properties (including high thermal and electrical conductivity, low gas permeability, high manufacturability, and relatively low cost materials); however, chemical instability due to the highly corrosive environment of the PEMFC leads to the formation of a passive surface oxide layer. Altering the surface by coating with a corrosion resistant material can be cost prohibitive when considering the amount of coating necessary to overcome the harsh conditions in a PEMFC, fabrication of the coating, and the number of plates in a stack. Less costly metals for coating, such as titanium, typically form an oxidative layer while non-corrosive metals can form pits where the underlying metal becomes exposed. Our multilayer technique combines both metal types for a corrosion resistant economical solution. [3] This design prevents oxide formation from percolating throughout the layered structure via thin films of non-corrosive layers alternated with thicker Ti layers. The specialized structure of multilayers of thin films (Au/Ti) allows the noncorrosive layer, the most costly, to be <1 nm while maintaining the viability and conductivity of the coating and the metal bipolar plate. [1] H. Tsuchiya and O. Kobayashi, “Mass production cost of PEM fuel cell by learning curve,” International Journal of Hydrogen Energy, 29 (2004) 985–990 [2] K. RoBerg and V. Trapp, “Graphite-based bipolar plates,” in Handbook of Fuel Cells Fundamentals, Technology and Applications, W. Vielstich, A. Lamm, and H. A. Gasteiger, Eds., JohnWiley & Sons (2003) 308–314 [3] S Wang, J. Peng, W. Lui, and J. Zhang, Performance of the Gold-plated Titanium Bipolar Plates for the Light Weight PEM fuel cells,” Journal of Power Sources 162 (2006) 486–491 SHAPE \\* MERGEFORMAT Figure 1. Multilayer design model. Figure 1