Site–selective, low-loading, Au nanoparticle-polyaniline hybrid coatings with enhanced corrosion resistance and conductivity for fuel cells

Ultralow loading of Au nanoparticles (0.038 mg cm^–2) and a polyaniline hybrid coating (AuNP-PANI) were deposited on stainless steel (SS316L) coupons. The unique two-step approach utilizing electrochemical deposition via cyclic voltammetry enabled growth of AuNPs in the fibrous PANI micropores thereby achieving enhanced surface coverage of SS316L and minimizing substrate corrosion via blocking of pores. The hybrid coatings revealed significantly low interfacial contact resistance values of 16.6 mΩ cm² (achieving the US DOE 2017 targets). Potentiodynamic tests revealed the excellent corrosion resistance of AuNP-PANI hybrid coatings with a corrosion potential of 0.61 V_SHE, which is positively shifted by 790 and 390 mV as compared to bare SS316L and PANI-SS316L, respectively. The corresponding potentiostatic corrosion current density of AuNP-PANI was reduced to 0.63 μA/cm² from 2.28 and 0.65 μA/cm² for bare SS316L and PANI-SS316L samples, respectively, thereby providing excellent stability in the cathodic polymer electrolyte fuel cell (PEFC) environment. Extensive electron microscopy and X-ray diffraction studies showed uniformly placed AuNP bundles with an average cluster size of 16 nm with Au (200) as the most prominent crystallite phase. Thermogravimetric studies revealed that the AuNPs did not affect the thermal stability of PANI which remained stable up to 260 °C which is well above the operating temperature of conventional PEFCs, making them highly suitable for coatings on bipolar plates for enhanced conductivity and corrosion resistance.