Estimation of lifetime and evaluation of (Co,Mn)3O4 coatings for IT-SOFC Steel Interconnects application by determining of Cr and O diffusion coefficients
EMSL Project ID
39734
Abstract
Intermediate temperature solid oxide fuel (IT-SOFC) are becoming increasingly attractive as a way of producing energy from a variety of fuels such as hydrogen and hydrocarbons, which can be used for generating electricity and heat. Although the operating concept of SOFC is rather simple, the selection of materials for the individual components presents enormous challenges. Each material must have the electrical properties required to perform its function in the cell and there must be enough chemical and structural stability to endure the fabrication and operation at high temperatures. The interconnect plays a key role in the planer SOFC, that physically separates the oxidant and fuel, distributes the gases to electrodes and provides electrical connections between single cells. The high operating temperature of the cell necessitates that the interconnect must meet the most stringent requirements such as high electrical conductivity , no porosity, thermal expansion compatibility, and inertness with respect to the other fuel cell components. The recent trend towards lower operating temperatures of SOFC may enable the use of metallic interconnects. The metallic interconnects promise lower cost, higher strength and higher electrical and thermal conductivity. Alloys of ferritic stainless steels and Cr based alloys are identified as the best suited materials for this purpose. However, under SOFC operating conditions volatile gaseous Cr species mainly CrO2(OH)2, CrO3 and CrO2(OH) are formed at the surface of the interconnect. These Cr species can interact with the cathode/electrolyte interface, thereby poisoning the cell operation. Furthermore metallic interconnects tend to form thermally grown oxide (TGO) that will ultimately weaken coating adhesion to the substrate, leading to delamination of coating and failure of the interconnect. Therefore, for improved oxidation, diffusing Cr resistance and electrical conductivity, either new alloys will be needed or surface engineering of existing alloys will be required. The proposed work falls in to the latter category, namely, the use of manganese cobaltite spinel (Mn,Co)3O4 (MCO) coatings to reduce the inward diffusion of oxygen and outward diffusion of chromium. These coatings have showed acceptably low electrical resistance and low Cr volatility. However, to get a reasonable estimate of the lifetime of such coatings, we need to determine quantitatively the diffusion coefficients for Cr and O in these coatings. To obtain reliable values for the diffusion coefficients of Cr and O in bulk MCO coatings requires the use of fully dense polycrystalline MCO, or perhaps even single crystal samples. The worked proposed here will integrate the experiment and atomistic computer simulations to determine these coefficients.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2010-10-01
End Date
2012-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Garratt E, S AlFaify, T Yoshitake, Y Katamune, M Bowden, MI Nandasiri, S Ghantasala, DC Mancini, S Thevuthasan, and A Kayani. 2013. "Effect Of Chromium Underlayer On The Properties Of Nano-Crystalline Diamond Films." Applied Physics Letters 102(1):Article No. 011913. doi:10.1063/1.4774086