CHARACTERIZATION AND TESTING OF A HIGH TEMPERATURE PROTON EXCHANGE MEMBRANE SINGLE CELL

Kurzfassung

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are considered a promising technology for hydrogen-based energy conversion due to their high operating temperature, improved tolerance to fuel impurities, and simplified water management compared with conventional low-temperature systems. However, the long-term durability of HT-PEMFCs remains a major challenge, particularly due to the corrosion of metallic bipolar plates in the phosphoric acid environment. Under these conditions, corrosion reactions may promote the formation of electrically resistive oxide- and phosphate-containing species layers, increasing the interfacial contact resistance (ICR) and reducing fuel cell performance. Consequently, the development of protective coatings capable of improving corrosion resistance while maintaining high electrical conductivity is essential for the advancement of durable and cost-effective HT-PEMFC systems.

This work focused on the development, characterization, and validation of carbon-based coatings for stainless-steel bipolar plates (SS BPPs) for HT-PEMFC applications. Coating formulations based on graphite, carbon black, PPSU, and solvent were optimized to achieve a balance between electrical conductivity, adhesion, and corrosion protection. The most promising coatings were integrated into a single-cell HT-PEMFC and evaluated under representative operating conditions. Fuel cell performance and durability were assessed using polarization curves, electrochemical impedance spectroscopy (EIS), ICR measurements, and post-mortem surface characterization.

The optimization of the coating formulations demonstrated that achieving an appropriate balance between conductive carbon content, polymer binder concentration, and coating thickness is essential to obtain both low interfacial contact resistance and adequate corrosion protection. The best performing coating achieved an ICR of 17.6 mΩ·cm-2 and reduced the performance degradation after 24 h of operation from 35.1 % for the uncoated SS BPPs to 22.5 % for the coated BPPs. In contrast, coatings providing insufficient protection resulted in higher ohmic losses and accelerated performance degradation, which may be associated with the formation of electrically resistive surface layers containing oxides and/or phosphates species, as seen with elemental analysis. Overall, the developed coating, deposited through a simple air-brushing process, represents a promising and cost-effective alternative for protecting metallic bipolar plates in HT-PEMFC systems.