Development of a niobium clad PEM fuel cell bipolar plate material

Reported in this paper are results obtained on a niobium clad material that is being developed for use in polymer electrolyte membrane fuel cell (PEMFC) stacks. A series of materials evaluation tests were initially conducted on niobium coupons to determine if this material was suitable as an external cladding layer exposed to a prototypic PEMFC environment. Results from corrosion testing conducted in 80∘C, 1 M H2SO4H2SO4 (with 2 ppm HF) display no measurable weight loss in the niobium specimens out to 2000 h of exposure. Interfacial contact resistance measurements conducted on as-received and post-exposed niobium indicate that it exhibits excellent surface conductivity (⩽10mΩcm2) under low clamping forces in both conditions. Polarization testing carried out under both prototypic anodic and cathodic PEMFC operating conditions suggest that the electrochemical behavior of niobium is comparable to that of platinum, with current densities of 2.7×10-52.7×10-5 and 6.3×10-9A/cm2 at half cell potentials of -0.1-0.1 and 0.6 V versus a saturated calomel reference electrode, respectively, under prototypic anode and cathode environmental conditions. Subsequent contact resistance and polarization testing of niobium clad stainless steel coupons yielded results similar to those found in monolithic niobium testing.