An experimental feasibility study of vanadium oxide films on metallic bipolar plates for the cold start enhancement of fuel cell vehicles

Abstract

An experimental study of vanadium oxide polycrystalline films deposited onto 316L stainless steel bipolar plates as an efficient Joule heating source for fuel cell vehicles was conducted by carefully modulating the negative temperature coefficients of the electrical resistance of the films at subzero temperatures. To fabricate the thin films, a well-mixed precursor solution of vanadium alkoxide and organic cosolvent was prepared by the hydrolytic sol-gel route and then coated on the pre-cleaned flat surface of 316L stainless steel plates with natural passive oxide layers by a dip-coating method. Subsequently, the variation of the nonlinear electrical resistance of the thin film was measured simultaneously over a wide temperature range of −20 to 80 °C, allowing direct detection of the surface temperature of the thin films. In addition, the adhesion, microstructures, compositions, and morphologies of the vanadium oxide thin films were investigated using the ASTM D3359 method, XRD, FE-SEM, and XPS analyses. A remarkable result from this study was that a temperature increase of 41.65 °C was induced by significant Joule heating of the vanadium sesquioxide films on metallic bipolar plates, i.e. approximately 1.8-folded more than the minimum requirement of Joule heating, at a current density of 0.1 A·cm−2 at −20 °C. Thus, it was concluded that thermal dissipation from the resistive vanadium oxide films with a negative temperature coefficient can be effectively used as a self-heating source to melt frozen water at subzero ambient temperatures, particularly for fuel cell vehicles.