Performance of Candidate Materials and Coatings for Thermal Management Systems for Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFC) require heat exchangers, pumps, valves and water separation devices to provide the functions of thermal and water management in the fuel cell balance of plant. Heat exchangers having relatively large surface areas are needed to cool the fuel cell engine at the low temperature differentials existing between the coolant and ambient air. All of these components must be durable in the deionized water environment prevalent within the water management system of the fuel cell. At the same time, contaminant-free cooling circuits are needed to prevent degradation of the fuel cell itself. Consequently, stainless steel or other exotic materials are conservatively specified in the deionized water circuits of current designs of fuel cell vehicles and power modules. The substitution of heavy and costly stainless steel components by aluminum would greatly benefit the implementation of PEMFCs as a competitive alternative energy source for motor vehicles. The focus of this paper is on selection and performance of materials for PEMFC heat exchanger applications. Candidate materials including stainless steel and aluminum alloys were investigated with respect to ionic contaminant release into deionized water coolants under simulated immersion and condensing heat exchange conditions. The effects of material composition, as-manufactured condition (brazing process method) and surface treatment (passivation) were characterized. The performance of selected organic and modified sol-gel coatings on aluminum substrates is also described. The coatings offered significant protection against the deionized water environment. Finally, the results of metallurgical investigations conducted on prototype heat exchangers recovered from fuel cell service are reported.