After more than 5½ years on test, fuelcellmaterials’ ChromLokTM interconnect coating has passed the 50,000 hour lifetime milestone. Back in 2011, we began Area Specific Resistance (ASR) testing of sample coupons coated with our manganese cobaltite (MCO) coating, which is an ideal coating for the cathode-side active area where electrical conductivity is critical because of its excellent oxidation and chromium volatility resistance, and high electrical conductivity. The chart below shows the ASR behavior of the MCO coated sample.
Figure 1. ASR behavior of MCO coated ferritic stainless steel at 800 C in humidified air and applied current density of 0.5 A/cm2.
Testing
As part of our rigid testing criteria, the test was conducted at 800 °C, in humidified air, with an applied current density of 0.5 A/cm2 on a typical ferritic stainless steel to determine the long-term stability of the coating. Thermal cycling and accelerated testing at a higher temperature (900 °C) were done on this part during the first 10,000 hours to simulate a longer time and confirm the robustness of the coating.
Microstructure
These images show the microstructure of the MCO interconnect coating before and after testing. The coating shows excellent stability after prolonged exposure to these harsh test conditions. The limited growth of the native chromia interfacial layer demonstrates the ChromLokTM coating’s excellent oxidation resistance, which is necessary to provide the required high temperature protection to enable ferritic stainless steel interconnects to be used in SOFC systems.
Figure 2. Cross-section SEM image and EDS compositional map of MCO coated ferritic stainless steel as processed (a), and after 50,000 hours isothermal ASR testing at 800 °C in humidified air.
About ChromLokTM
The ChromLokTM system provides metallic components used in solid-oxide fuel cell systems with protection at high temperatures. The ChromLokTM system includes a range of complementary oxide coatings that prevent the release of detrimental chromium species from stainless steels during high temperature operation. While other corrosion protection methods create oxidation resistant surfaces, contact resistance is increased. ChromLokTM coated surfaces remain electrically conducting for years under harsh temperature conditions.
The ChromLokTM coating was designed to provide peace of mind by allowing no poisoning of downstream components as well as with an eye on larger volume production by providing a scalable coating manufacturing process and allowing longer stack life. Without a stable cathode active area coating, oxidation of the resistive chromia layer would readily occur resulting in a rapid increase in cell resistance limiting the performance and lifetime of the stack.
fuelcellmaterials’ ChromLokTM system protects interconnects from high temperature oxidation and chromium volatility and increases their lifetime. Addressing this degradation mechanism increases the service lifetime of the SOFC system enabling stack developers to offer longer warranty periods for the systems. fuelcellmaterials’ ChromLokTM technology addresses a key mechanism that limits the service lifetime of these systems and allows you to move on and focus on other issues.
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