Effects of Al incorporation on the interfacial conductivity and corrosion resistance of CrN film on SS316L as bipolar plates for proton exchange membrane fuel cells

Abstract

Interfacial conductivity and corrosion resistance of bipolar plates are two significant parameters affecting the performance and durability of proton exchange membrane fuel cells. This study designs to investigate the effects of Al incorporation on the interfacial conductivity and corrosion resistance of CrN film coated on bipolar plates, ternary Cr–Al–N films with different Al content have been deposited on SS316L samples by closed unbalanced magnetron sputter ion plating (CFUBMSIP). Al content was adjusted by altering magnetron sputtering current of Al target. Scanning electron microscopy (SEM) results show that the deposited films are dense and continuous. The phase structures and bonding types before and after Al incorporation have also been investigated by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Interfacial contact resistance (ICR) between gas diffusion layer (GDL) and coated samples increases with the increase of Al content doped in CrN film, and the lowest ICR value is 5.1 mΩ cm2 at 1.4 MPa. The incorporation of Al has influence on the interfacial conductivity of CrN films by combining two competitive aspects actual contact area and the conductivity of the sample surface. Potentiodynamic polarization tests in the simulated corrosive circumstance of PEMFCs reveal that the corrosion potential of coated sample become more positive after Al incorporation and the corrosion current density obtained from Al doped CrN film after potentiostatic tests in cathode PEMFCs environment is 0.021 μA cm−2, which witnesses nearly one order of magnitude decrease compared with CrN without Al content. Electrochemical corrosion tests and inductively coupled plasma-mass spectrometry (ICP-MS) detection disclose that Al doped CrN film can improve the durability of bipolar plates by forming a dense passive film in real PEMFCs environments and reduce the metal ion contamination of membrane. Based on the results of ICR and electrochemical corrosion tests, it is demonstrated that low content of Al incorporation in CrN film can combine the two aspects, namely, better corrosion resistance and high interfacial conductivity which are beneficial for the commercial application of metallic bipolar plates.