Protective layer coatings for solid oxide fuel cell interconnects by Inkjet printing

Pandiyan, Sathish (2020). Protective layer coatings for solid oxide fuel cell interconnects by Inkjet printing. University of Birmingham. Ph.D.

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Abstract

Interconnects form an integral part of the solid oxide fuel cell (SOFC); they provide structural support and electrical connection between individual fuel cell units in a stack. Currently, ferritic based stainless steels (FSSs) are considered as the standard interconnect materials. FSSs forms a protective chromia layer in SOFC cathode conditions at high-temperature operation. The thermally grown oxide layer slows down the oxidation and offers resistance against high-temperature corrosion. However, the thermally grown oxide layer (chromia) formed during the operation of SOFC stacks leads to a continuous degradation in key properties of the FSS interconnect material. Consequently, leading to volatilisation of chromium from the oxide scale with subsequent chromium poisoning of the cathode, and increased electrical contact resistance. To overcome these degradation mechanisms, mitigation methods such as the development of conductive and protective coatings, surface treatment/ modifications, and alloy development are being continuously studied. In this study, inkjet printing technology, a novel, very flexible, and low-cost approach to the coating was employed for the application of protective layer coatings on SOFC metallic interconnects.

The work presented focusses on the formulation of aqueous-based spinel particulate inks for the inkjet printing process using an electro-magnetic inkjet printer. An ink formulation route based on a two-stage ball milling technique was developed to produce a printable ink composition with Manganese Cobalt Oxide (MnCo2O4, MCO), Manganese Cobalt Ferrite (MnCo1.8Fe0.2O4, MCF) and copper doped MCF (MnCo1.6Fe0.2Cu0.2, MCFC) spinels as the coating materials. The printability of the formulated inks was demonstrated by printing them on stainless-steel substrates (K41 and Crofer 22H) and their performance as a protective layer was evaluated based on high-temperature oxidation and area-specific resistance (ASR) measurements The high-temperature tests were performed at 700 °C in the air with 3% humidity for 1000 hours, simulating SOFC operating conditions at the cathode side. The performance of the printed layers was assessed based on ASR values and chromium retention. The effect of surface plasma nitriding on K41 stainless steel substrates was studied under similar test conditions. With ASR reduced to a level ~ 0.05Ω cm2 and chromium concentration in the getter (cathode) material below 1 atomic%, close to the detection threshold, the protective layers produced would qualify for SOFC applications.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):