Effect and mechanism of bias voltage on microstructure and corrosion resistance of CrxNy coatings in proton-exchange membrane fuel cells

Abstract

The key factor limiting the long-term commercial application of CrxNy coatings in the PEMFC is that these coatings easily grow into coarse columnar crystals with subsequent microcracks and pinholes, leading to a sharp decrease in corrosion resistance performance. In this view, a series of different substrate bias voltages were applied to deal with this problem. The results demonstrated that with applying a -120 V bias voltage on the substrate, the adhesion strength is double that of the CrxNy coating without bias voltage. In addition, the -120V-CrxNy sample exhibits the lowest corrosion current density of 0.65 μA/cm2 and a minimum ICR value of 5.87 mΩ·cm2, thus highly meeting the U.S. DOE 2025 targets. Moreover, the CrxNy coatings subjected to bias voltages ranging from -100 V to -140 V exhibit excellent durability and stability, with current densities that are 1-2 orders of magnitude lower compared to the 0V-CrxNy coatings. Therefore, this work provides a novel approach to control the growth of columnar crystals in CrxNy coatings for future PEMFC manufacturing processes, and has important reference value for the regulation of columnar crystals in other coatings such as TiN, NbN, AlN, etc.