Corrosion test results of the selected coatings (D3.3)
Interconnectors in solid oxide electrolysers (SOEL) are typically manufactured using ferritic
stainless steels with a chromium content of 18–22 wt-%. This composition allows the steel to
form a protective Cr-rich oxide scale, typically Cr2O3, at elevated temperatures. However, under
certain conditions and in the presence of water vapor, the scale can form volatile hydroxide
compounds, such as CrO2(OH)2 and CrO2(OH). These hydroxides are transported to the active air
electrode, where they form (Sr,Cr)-oxide compounds, causing Cr-poisoning and leading to
degradation. Additionally, the formation of Cr-rich scales increases ohmic resistance, which
directly impacts stack performance.
To prevent degradation and performance issues, interconnects are coated with ceramic-based
protective coatings. These coatings act as a barrier, preventing Cr2O3 from reacting with water
vapor to form volatile species. They also reduce the growth rate of Cr-rich scales, enabling
improving stack performance and extending operational lifetime.
One of the objectives of the PilotSOEL project is to identify cobalt-free coating candidates to
replace commonly used manganese-cobalt spinels. Cobalt is classified as a critical raw material
(CRM) and is known for its carcinogenic properties. A wide range of coating candidates was
reviewed in Deliverable 3.1: List of coating candidates for air and fuel sides of interconnect plates,
based on scientific literature related to solid oxide fuel cell and electrolyser technologies. Four
candidates were selected for further study using various ex-situ methods that simulate actual
stack operating conditions. At least one of these coatings should meet the key performance
indicators (KPIs) set for this project by achieving an ASR value lower than 5 mΩ*cm² after 3000
hours of operation.