Due to its particular characteristics (low operation temperature among others), proton exchange membrane (PEM) is the ideal type of fuel cells to be used in portable applications. In these cases, high power density (kW/kg) and hence, low weight is essential to achieve reasonable efficiencies. In order to reduce the weight, a good choice of materials to manufacture the bipolar plates is required, as they account for around 80% of the total weight of a stack. Non-porous graphite is probably the most commonly used material for BP production, but it suffers from low transversal electric conductivity and very limited thermal conductivity. Other materials used are graphite-based composites and metals such as stainless steel and Ni-based alloys. Even when metallic bipolar plates can be manufactured in very thin sheets, its very high density can unfortunately be a problem. A very good candidate for metal-based bipolar plates is aluminum, due to its very low density and both good electric and thermal conductivity. However, the very harsh environmental conditions inside a PEMFC (pH of 2-3 at a temperature close to 80°C, and high humidity levels) quickly attacks the plate surface, reducing the life-time, and forming a non-conductive oxide layer that increases both the ohmic and contact resistances of the cells. To overcome these problems a surface coating has to be deposited. In this work, the performance of several coatings applied to the aluminum bipolar plates of a small stack is tested. The analyzed options are chemical nickel, and three conductive- ceramics such as tungsten carbide, chromium nitride and Zr-Cr nitride.
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