Mid Term Report Publishable Summary - CORDIS · D8.3 – Mid-Term Report – Publishable Summary page 3 of 6 SCORED 2:0, 1st Periodic Activity Report, 01.07.2013-31.12.2014 PUBLIC

SCORED 2:0

Steel COatings For REducing Degradation

Deliverable D 8.3

Mid‐Term Report – Publishable Summary

prepared by:

University of Birmingham

VTT

ENEA

EPFL

Teer Coating Ltd

Turbocoating

SOLIDpower

Submission date: 05.03.2015

Status: final

Date prepared: 05.03.2015

Responsible editors: Jong‐Eun Hong, Robert Steinberger‐Wilckens (UBHAM)

Start date of project: 01.07.2013 Duration: 36 months

Dissemination Level PU Public X

PP Restricted to other programme participants (including the Commission Services)

RE Restricted to a group specified by the consortium (including the Commission Services)

CO Confidential, only for members of the consortium (including the Commission Services)

D8.3 – Mid-Term Report – Publishable Summary page 2 of 6

SCORED 2:0, 1st Periodic Activity Report, 01.07.2013-31.12.2014 PUBLIC

1 Project abstract

The economic viability and market place entry of SOFC power systems is directly dependent on their longevity and production costs. Adequate operational life spans can only be achieved, if the performance degradation of the SOFC stacks and Balance of Plant components over time can be considerably reduced. At the same time, manufacturing costs have to be lowered dramatically for the specifically necessary components securing the long component service life.

As of now, chromium deactivation of the cathode is considered one of the major contributions to the degradation of SOFC stacks. Since chromium steels, on the other hand, are an essential material in reducing stack costs, methods have to be found to make best use of their advantages whilst avoiding chromium transport to the cathode.

Balance of Plant components upstream of the cathode also contribute to the chromium immission, a fact that is often overseen and requires protective coatings also for any components situated in the air flow pathway to the cathode. Finally, the build‐up of oxide scales will influence the electrical resistance and contact resistance thus requiring coatings for the stabilisation of the contacts on both cathode and anode side of the SOFC cell.

Within the project Real‐SOFC first steps have been made towards developing suitable combinations of steels and coatings. It has become apparent that any steel will require a coating in order to sufficiently reduce

chromium evaporation and oxide layer build‐up, and also sustain a low surface resistivity. More recently, a variety of new coating techniques have been reported that require further evaluation under SOFC relevant operating conditions.

ScoReD 2:0 aims to further elaborate on the production of coated steel components showing markedly improved properties with regard to chromium release, electrical resistivity and scale growth. The focus of ScoReD 2:0 will be on choosing optimised combinations of protective layer materials with different steel qualities (including low‐cost options) and analysing the influence, practicality and cost of different methods of coating. Also in understanding which factors influence the efficacy of such coatings.

Acknowledgment:

The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007‐2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no. 325331.



2 Publishable summary

High temperature corrosion is a crucial problem in operating solid oxide fuel cell (SOFC) systems. In particular, the chromium poisoning of the air electrode (cathode) is recognised as one of more serious contributions to the performance degradation of SOFC devices. Stainless steel is generally used as interconnect (IC) material and chromium evaporating from these high chromium steels deposits within the cathode leading formation of chromia and chromium manganese spinels (depending on cathode materials). These lead to blocking of pores, reduction of electrical conductivity, and deactivation of the cathode material resulting in serious degradation of performance. This form of degradation has been shown to be one of the main causes that prevent SOFC from having a sufficient operational life for stationary applications, which essentially require ten years of lifetime. In addition to the cathode poisoning problem, corrosion issues on the IC material itself also negatively affect the fuel electrode-interconnect components in that the electrical resistance increases, thereby contributing to reducing the performance. On the other hand, since chromium steels are an essential material in reducing stack costs, methods have to be found to make the best use of their advantages in order to bring this technology to market whilst avoiding chromium poisoning and corrosion.

SCoReD 2:0 aims to optimise the properties of the coated steel interconnects with respect to maximising long-term SOFC operation, to acquire a deeper understanding of the process of surface property modification by coating protective layers and to develop test methods to rapidly characterise these properties (accelerated testing). In addition, analysis of the commercial potential on the technical solutions will contribute to bridging the gap to industrialisation. Accordingly, a major step forward in achieving the SOFC device lifetime deemed necessary to achieve realistic market entry economics for stationary applications can be achieved. In this aspect, the focus of SCoReD 2:0 is on choosing optimised combinations of protective layer materials with different steel qualities (including low-cost options), analysing the influence, practicality and cost of different methods of coating and understanding which factors influence the efficacy of such coatings.

Within the project, protective coatings are applied to a selection of steels relevant to SOFC and BoP manufacturing by using various coating methods such as dip coating, wet powder spraying (WPS), spray coating, atmospheric plasma spraying (APS), physical vapour deposition (PVD), and atomic layer deposition (ALD) methods. Coated steel samples are provided for standard tests of high temperature oxidation (exposure), area specific resistance (ASR), chromium evaporation, conductivity and thermal cycle followed by post-test analysis of the tested samples. A best layer deposition process is then defined with regard to coating quality, performance and cost. After verification of the best combination of protective layer, interconnect steel and coating method, concept tests of single cell repeat unit (SRU) and prototype SOFC stacks are conducted to demonstrate stack lifetime of ca.10,000 hours (and longer after the project has terminated) and industrial mass production cost reduction for the processes applied. A model is also established with respect to thermochemical behaviour, oxidation kinetics, and life time of the steel interconnects based on the results of post-test analysis on standard and concept test samples. In addition, accelerated testing methods are developed for lifetime prediction towards 10 to 15 years of operation (stack and system, respectively) with coated interconnects. This work will directly address the topics of reliability, durability and cost effectiveness for components used in SOFC stack and Balance of Plant manufacture.



- Schematic diagram of SCoReD 2:0 work flow -

This project consists of eight work packages (WPs) in total of which WP 8 deals with the overall technical management and project coordination. Results of each WP carried out for the first period are summarized as below.

WP 1 – Sample Supply

During the first period of the project, a coating powder of manganese cobalt oxide (MCO) prepared by a solid state reaction using ball milling was supplied for coating partners to deposit Generation 1 (Gen 1) coatings. Metallic interconnect steel samples of different suppliers (K41/441 and Sandvik Sanergy HT) and size (100x100x0.2 mm and 10x10x1 mm) were provided for the coatings. In addition, a general logistics of delivering materials and samples among partners was elaborated.

WP 2 - Coating Application Development (wet chemical methods)

ENEA, University of Birmingham (UBHAM) and SOFCPOWER SPA (recently altered to SOLIDPOWER SPA: SPOWER) are responsible for coating steel samples using wet chemical methods such as dip coating, WPS coating which are favourable for mass production due to the simplicity and cost-effectiveness of the processes. Gen 1 samples were successfully prepared using MCO coatings by partners apart from ENEA which applied La/Fe perovskite coatings. In addition, UBHAM investigated the effect of an MnOx sublayer in addition to MCO layer on layer adhesion, ASR and Cr retention properties.

WP 3 - Coating Application Development (plasma and thermal spray methods)

Turbocoating (TC) is responsible for coating using plasma and thermal spray methods. During the first period, TC has tested atmospheric plasma spray (APS), high velocity oxygen fuel (HVOF) and low vacuum plasma spary (LVPS). However LVPS could not provide better results than APS. In addition, since Ni coatings were excluded in Gen 1 samples, HVOF technique that was employed for the deposition of Ni coatings was excluded. Thus, APS technique is applied for further tests and Gen 1 coatings were successfully deposited.



WP 4 - Coating Application Development (sputtering, PVD and CVD methods)

Teer Coating Limited (TCL) and VTT are responsible for coating steel interconnects using physical vapour deposition (PVD) and atomic layer deposition (ALD) methods. Both techniques allowed to prepare thin, dense coating samples. In addition to TCL’s conventional PVD coating activities, an additional surface treatment using low pressure pulsed plasma nitriding on steel surfaces was investigated. Plasma nitriding of a steel surface is known to improve the surface strength in terms of high hardness and wear resistance, minimize the interfacial contact resistance and stabilize the surface composition after high temperature exposure. Therefore a pulse plasma nitriding process in combination with separate PVD coatings were considered by TCL as suitable objectives for the project.

WP 5 - SOFC relevant Corrosion Testing and Accelerated Testing

VTT, UBHAM, ENEA and EPFL are responsible for WP 5. Samples from WPs 2, 3, and 4 were tested with different methods, including:

- Visual inspection of samples for bending, coverage, and uniformity

- High temperature exposure (700 °C, 1000 h) combined with post-test microscopy

- High temperature electrical resistance measurement (700 °C, 1000 h) combined with post test microscopy

- High temperature chromium retention test (700 °C, 1000 h) combined with post-test microscopy

- Adhesion tests at room temperature.

- Schematic diagram of ASR/Cr-retention measurement -

A standard exposure test apparatus was successfully established which is also available for an acceleration test varying humidity and temperature. In addition, a novel characterization method was developed to test high temperature electrical resistance and chromium retention within this project. This method replicates the stack conditions and materials as closely as possible where a coated steel plate is in contact with a cathode (lathanum strontium cobaltite: LSC) coated palladium plate. Cr evaporation from the steel and reaction with the cathode happen identically with a real SOFC stack. Test conditions were: 700 °C, 1000 h,



current density 0.4 A/cm2, compression 0.4 MPa, humidity 3%, and air atmosphere. TC and TCL samples revealed lower ASR values compared with the other samples. After test all samples were provided for post-test analysis.

WP 6 – Post-Test Analysis

EPFL, VTT, ENEA, TC, and UBHAM are responsible for WP 6. The post-test analyses were performed using X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) on small test pieces that underwent exposure tests and ASR/Cr retention tests. Among all the steel/protective coating couples investigated so far, most samples fulfilled the criterion of chromium retention apart from samples of VTT, ENEA and SPOWER. In summary, combined with results of ASR and chromium retention, the reference Sandvik Sanergy HT with Ce/Co layer remains at the moment the best choice, but the TC and TCL samples are close.

- Summary of ASR values vs the chromium diffusion in LSC on tested samples -

WP 7 – Stacks proof of concept testing

SPOWER, TCL, UBHAM, ENEA and TC are responsible for testing proof-of-concept stacks. However, the testing has been deferred to the second half of project when the selection of coatings can be performed on a more educated basis. SPOWER has already assembled and validated a bench for testing stacks.

WP 8 – Management and Miscellaneous Activities

General management activities have been done by UBHAM to ensure the smooth and successful running of the project. The Test matrix has been updated properly and the project web site has been lanunched for internal abd external communication.

Several meetings and workshops were held to decide and manage the test matrix, and map progress of the project.

Documents

Mid Term Report Publishable Summary - CORDIS · D8.3 – Mid-Term Report – Publishable Summary page 3 of 6 SCORED 2:0, 1st Periodic Activity Report, 01.07.2013-31.12.2014 PUBLIC