ABSTRACT

An alternative for costly platinized titanium might be surface treated stainless steel or titanium. The paper presents latest results of corrosion tests in simulated PEMFC environment that were done on palladium enriched titanium. Surface treatment of titanium grade 7, which enriched the surface with Pd from Ti matrix, did not affect excellent corrosion resistance, but reduced the contact resistance down to 350 mΩ·cm2 after the potentiostatic polarization in simulated PEMFC environment. Although the US DOE target for contact resistance was not achieved (10 mΩ·cm2), samples for single cell test were fabricated to evaluate the impact on the FC efficiency and single-cell test passed successfully. Interfacial contact resistance is a critical parameter in both the cases. Not only from PEMFC functionality point of view but also in terms of correct procedure for collecting the data.

INTRODUCTION

Nowadays an increasing attention to the development of electrical vehicles is obvious due to changes in the environmental conditions. The source of energy is a very important part of these alternative solutions. The proton exchange membrane fuel cell (PEMFC) offers a solution with many advantages, such as minimum exhaust emissions, low noise, quick commissioning, low operating temperature (approx. 80°C) and high energy efficiency. On the other hand, these positive properties must be confronted with high cost of the cells [1-8].

Very important part of PEMFC are bipolar plates, that act as current collectors and gas and heat distributors in the cell. Materials for bipolar plates should have high corrosion resistance to eliminate damaging of the proton exchange membrane by cations when PEMFC is running and good electrical conductivity to minimize electrical loses. Every material for bipolar plates aims to meet DOE (U.S. Department of Energy) technological targets for corrosion rate (j<1μA·cm−2) and interfacial contact resistance (ICR<10mΩ·cm2). Titanium could be a one of the materials, which can substitute a brittle graphite, which is more suitable for stationary usage of PEMFC, or currently used coated stainless steel in automotive application. The mechanical properties are important due to construction PEMFC for unique vehicles [9]. Titanium has low density (4.51 g·cm−3), excellent corrosion resistance and its ions are less toxic for membrane, than, for example, ions released from stainless steel. These properties put titanium among the appropriate materials for bipolar plates. Titanium exposed to aggressive environment can form an oxide film (TiO2). This film is durable also in acidic environment of PEMFC (pH 2 – 3, 80°C) containing anions such as HCO3, HSO4, SO42−, F etc., dissolved from the membrane and MEA. Even though this film has good corrosion resistance properties, it has lower conductivity and higher ICR than titanium. In this point of view, the surface treatment of titanium is very important step in the process of increasing efficiency of PEMFC with titanium bipolar plates[2-6].

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