The influence of anodizing temperature and current density on the corrosion resistance of AAO/Ni-Ag composite coating on AA5052 surface for bipolar plate PEM FC

The bipolar plate acts as a critical element in the Proton Exchange Membrane Fuel Cell (PEMFC) system, constituting 60-80% of the total weight of a PEMFC stack. In recent years, there has been a growing interest in exploring aluminum alloys for bipolar plates. The only crucial challenge for aluminum bipolar plates is their inferior corrosion resistance in the acid environment of PEMFC. This study aims to enhance the corrosion resistance of AA5052 plates by AAO/Ni-Ag coating for PEMFC application. The fabrication of AAO was carried out by anodizing process in 16% H2SO4 at 25, 0, and -25°C with the current densities of 10 and 20 A/dm2 for 30 minutes. Subsequently, the electrodeposition of Ni-Ag on anodized AA5052 was conducted in a solution containing 240 g/L NiSO4⋅6H2O and 7.5 g/L AgNO3 with the current density of 2 A/dm2 at room temperature for 15 minutes. The corrosion properties of the integrated coating were investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic test in a solution of 0.5M H2SO4 with 2 ppm HF at ambient temperature. The findings demonstrated that the incorporation of a protective layer on AA5052 substrates substantially enhanced the ability of bipolar plates to withstand corrosion in the fuel cell’s operational conditions in comparison to substrates without any coating. The substrate, when subjected to an anodizing current density of 20 A/dm2 and a temperature of -25°C, exhibited superior performance. Its corrosion rate was 20 times lower compared to an uncoated substrate, and the Nyquist Curves displayed a larger curve and higher impedance value.