Final Report Summary - SCORED 2:0 (Steel Coatings For Reducing Degradation in SOFC)
Executive 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 the key contributions to the continuous performance degradation of SOFC devices that limits their lifetime. Stainless steel is generally used as interconnect (IC) material and chromium evaporating from these high chromium steels deposits within the cathode leading to formation of chromia and chromium spinels (depending on cathode materials). These lead to blocking of pores, reduction of electrical conductivity, and deactivation of the cathode material resulting in continuous degradation of performance. This form of degradation has been shown to be one of the main causes to be overcome to equip SOFC for stationary applications, which essentially require ten years of operational lifetime. In addition to the cathode poisoning problem, corrosion issues on the IC material itself also negatively affect the electrode-interconnect contacting in that the electrical resistance increases, thereby contributing to reduced 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 the market whilst avoiding chromium poisoning and corrosion issues.
The SCoReD 2:0 project, running from 2013 to 2017, aimed 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). It directly addressed the topics of reliability, durability and cost effectiveness for components used in SOFC stack and Balance of Plant manufacture.
The focus of SCoReD 2:0 was on choosing optimised combinations of protective layer materials with different steel qualities (including low-cost options) and coating processes, 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 were 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), atmospheric plasma spraying (APS), physical vapour deposition (PVD), and atomic layer deposition (ALD) methods. Coated steel samples were provided for standard tests of high temperature oxidation (exposure), area specific resistance (ASR), chromium evaporation, and bulk conductivity followed by post-test analysis of the tested samples. The best layer deposition processes were then selected 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 prototype SOFC stacks were successfully conducted to demonstrate stack lifetime of over 10,000 hours and industrial mass production cost reduction for the processes applied. A model was 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 were proposed for life-time prediction towards 10 to 15 years of operation (stack and system, respectively) with coated interconnects.
Project Outcomes
The proof-of-concept was performed on two stacks with 6 layers each, one of which operated for over 11,000 h within the project duration.
The benchmark of an ASR of 5 mΩ cm2 combined with a chromium diffusion of less than 1 weight% into the LSC material was accomplished by several powder applications by APS and PVD methods on all types of steel. Lower values were even obtained on the Sanergy HT and CroFer H steels. WPS application with MCFC powders came close. Samples with pre-nitriding achieved values below 20 mΩ cm2 but delivered more consistent results in the stack tests with negligible differences between individual layer performance.
The Lucerne SOFC Forum 2016 saw a high number of contributions from this project. The project partners delivered 35 journal papers, conference papers and conference contributions (talks and posters) to disseminate the project results. Exploitation will be performed by the companies involved in their day-to-day business and by the universities in their continued research activities.
Summary Conclusions
The Scored 2:0 project has demonstrated the possibility of using low-cost ferritic stainless steels such as K41 and 441 in combination with different coatings and deposition techniques.
Lab scale tests allowed to evaluate several interesting technologies such as ALD or Dip coating in molten salts but did not allow the application on real interconnects due to the small size of the reactors.
The technologies resulted to be viable for coating real interconnects are:
- Spray coating (SOLIDpower),
- Plasma spray (Turbocoating),
- Magnetron sputtering (Teer Coating Limited).
The results obtained from the project show that, despite the porosity of coatings obtained through wet chemical methods, the degradation observed over long-term stack tests is almost comparable to that obtained by PVD / CVD methods. Most likely the effect of a dense coating obtained with PVD / CVD methods is more noticeable in terms of stack degradation after 30,000 hours or more.
Lower grade steels (K41/441) come very close to the higher grades (Sanergy HT and Crofer 22 H) and in some few cases performed better. Statistics would need to further prove the reliability of these statements. In any case it can be deducted that the lower grade steels require a physically sealing protective coating (APS & PVD) whereas the higher grade steels can also deliver excellent ASR values with WPS applied layers, if they are sufficiently densified.
Project Context and Objectives:
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 the key contributions to the continuous performance degradation of SOFC devices that limits their lifetime. Stainless steel is generally used as interconnect (IC) material and chromium evaporating from these high chromium steels deposits within the cathode leading to formation of chromia and chromium spinels (depending on cathode materials). These lead to blocking of pores, reduction of electrical conductivity, and deactivation of the cathode material resulting in continuous degradation of performance. This form of degradation has been shown to be one of the main causes to be overcome to equip SOFC for stationary applications, which essentially require ten years of operational lifetime. In addition to the cathode poisoning problem, corrosion issues on the IC material itself also negatively affect the electrode-interconnect contacting in that the electrical resistance increases, thereby contributing to reduced 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 the market whilst avoiding chromium poisoning and corrosion issues.
The SCoReD 2:0 project, running from 2013 to 2017, aimed 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). It directly addressed the topics of reliability, durability and cost effectiveness for components used in SOFC stack and Balance of Plant manufacture.
The focus of SCoReD 2:0 was on choosing optimised combinations of protective layer materials with different steel qualities (including low-cost options) and coating processes, 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 were 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), atmospheric plasma spraying (APS), physical vapour deposition (PVD), and atomic layer deposition (ALD) methods. Coated steel samples were provided for standard tests of high temperature oxidation (exposure), area specific resistance (ASR), chromium evaporation, and bulk conductivity followed by post-test analysis of the tested samples. The best layer deposition processes were then selected 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 prototype SOFC stacks were successfully conducted to demonstrate stack lifetime of over 10,000 hours and industrial mass production cost reduction for the processes applied. A model was 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 were proposed for life-time prediction towards 10 to 15 years of operation (stack and system, respectively) with coated interconnects.
More details of the full project report are found in the final report deliverable D8.4.
Project Results:
This project consisted of eight work packages (WPs) in total, including one WP dealing with the overall technical management and project coordination. Results of each WP carried out for the second period (01/01/2015 to 30/06/2017) are summarised as below. More details of the full project report are found in the final report deliverable D8.4 and in the full periodic report for P2.
WP 1 – Sample Supply
During the second period of the project, coating powders of manganese cobalt oxide (MCO) doped with iron (MCF, Gen 3) and iron and copper (MCFC, Gen 4) were applied. Metallic interconnect steel samples of different suppliers (K41/441, Sandvik Sanergy HT, and CroFer H) and size (100x100x0.2 mm3 and 10x10x1 mm3) were provided for the coatings. Powders were sourced from the commercial suppliers and to some limited extent (G4) synthesised within the project. The Gen 5 samples were prepared on the basis of surface nitrided samples prepared by Teer Coating Limited (TCL/MIBA) using MCF powders.
WP 2 - Coating Application Development (wet chemical methods)
ENEA, University of Birmingham (UBHAM), and SOFCPower (SPower) were responsible for coating steel samples using wet chemical methods such as dip coating, WPS coating, and inkjet printing which are favourable for mass production due to the simplicity and cost-effectiveness of the processes. Gen 3/4/5 samples were prepared by WPS/inkjet methods. ENEA applied their La/Fe perovskite surface treatment. The addition of copper as sintering aid to the WPS powders improved the performce by increased densification. On the other hand, dip coating was less successful and could not be proven on prototype stack parts due to the limited size of samples that could be treated.
WP 3 - Coating Application Development (plasma and thermal spray methods)
Turbocoating (TC) used plasma spray methods (APS) to prepare Gen 3/4/5 samples. These displayed the best performance in ex-situ testing and this technique was tested on several layers within the proof-of-concept stacks.
WP 4 - Coating Application Development (sputtering, PVD and CVD methods)
Teer Coating Limited (TCL) and VTT were responsible for coating steel interconnects using physical vapour deposition (PVD) and atomic layer deposition (ALD) methods, repsectively. The PVD coatings showed excellent behaviour whereas the ALD did not match up to expectations. PVD coatings were also trialled in the proof-of-concept stacks.
TCL introduced plasma nitriding of steel surfaces in Period 1 - this proved to be beneficial to contact resistance and was also included in stack tests. It proved to deliver more consistent properties of the interconnect coatings in the in-situ (stack) tests.
WP 5 - SOFC relevant Corrosion Testing and Accelerated Testing
VTT, UBHAM, ENEA, and EPFL performed tests on samples originating from WPs 2, 3, and 4 with different methods, including:
- High temperature exposure (700 °C, 1000 h) followed by post-test microscopy,
- High temperature electrical resistance (ASR) measurement (700 °C, 1000 h) followed by post test microscopy,
- High temperature chromium retention test (700 °C, 1000 h) followed by post-test microscopy,
- Adhesion tests at room temperature.
A standard exposure test apparatus was established, also available for an acceleration test varying humidity and temperature. In addition, a novel characterisation method was developed to test high temperature electrical resistance and chromium retention (Fig. 2). This method replicates the stack conditions and materials as closely as possible. A coated steel plate is in contact with a cathode (lanthanum strontium cobaltite: LSC) coated palladium plate. Cr diffusing from the steel and reacting with the cathode happen in an identical way as in a real SOFC stack in the contact areas. 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 consistently showed lower ASR values compared with the other samples.
WP 6 – Post-Test Analysis
EPFL, VTT, ENEA, TC, and UBHAM performed post-test analyses 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, 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 the benchmark choice at 5 mΩ cm2, with the TC (APS) and TCL (PVD) samples delivering equivalent or better performance.
WP 7 – Stacks proof of concept testing
Several stacks were built by SPOWER as proof-of-concept stacks and tested for several thousand hours, the longest running for 11,000 hours with limited degradation.
WP 8 – Management and Miscellaneous Activities
A multitude of meetings and TelCo's were held to map progress of the project and take the imminent decisions on the stack testing.
The Lucerne SOFC Forum 2016 saw a high number of contributions from this project.
Potential Impact:
The project was industrially oriented and targeted commercial exploitation as required by the FCH JU guidelines and calls.
The work in the project fell into two categories
- basic research and understanding of materials and processes, and
- industrially focussed development of processes.
In so far there were two strategies of dissemination:
- the usual proliferation of scientific results and insights via conference presentations and papers (see final section), journal papers etc., and
- the constrained dissemination of industrial confidential developments in order to protect the competitiveness and cutting edge technology development of the industrial partners.
The project struck a reasonable balance between the two with a firmly installed procedure of gaining permission to publish vis a vis the justified interests of the industrial partners in confidentiality.
Project results were presented at conferences, at workshops, and at the final project event.
In order to propagate the findings and advertise the successes, a number of workshop contributions (e.g. to the series of Bruges workshops on SOFC systems run annually by U B’ham, VTT and Research Centre Jülich within the EERA context) and conference papers (ECS SOFC symposia and Lucerne SOFC Forum events) were prepared.
The tables in Part A show the project related publications, conference contributions, and events.
Dissemination by other means
Type Date Lead responsible Comments
mail shot Jan 2016 UBHAM advertising the April 2016 workshop and disseminating project results
mail shot April 2016 UBHAM advertising the Lucerne 2016 session and any workshop outcomes, and disseminating project results
mail shot Jan 2017 UBHAM advertising the April 2017 workshop and disseminating final project results
recipients of mail shots would include the FCH JU members (IG and N.ERGHY) as well as the wider SOFC community (Europe, U.S.A. Asia) as reached by FCH JU mail-outs and own mailing lists.
Exploitation of project results
The results of the project will be
- viable for mass production and low-cost manufacturing
- provide evidence of realistic component life and maintenance cycle consistent with system life >10 years (subject to the verification methodology and lifetime models developed) and consistent with market acceptance requirements
Benchmarking figures for success verification include:
- allowing for fuel utilisations of >90% (as far as specific SOFC cells and stacks allow) based on passivation of steel interconnects and tolerance to extreme water content
- therefore allowing for high system efficiency (depending also on both the SOFC cell efficiency and the BoP parasitic losses)
- achievement of low cost manufacturing
- achievement of high system lifetime and low cost of maintenance by avoiding mid-term replacement of stack
- development of lifetime prediction models for steel parts for optimised lifetime engineering
The potential for commercially exploiting the project results is high considering the high value of the issues mentioned above to all SOFC developers and manufacturers.
Commercial exploitation is directly given through the current commercial activities of the three industry partners. The two coating companies can directly implement results in their processes and/or adopt new processes if proven superior (and commercially viable). The stack manufacturer will integrate successful materials combinations into their design and has a vital interest in lower cost steels since these constitute a overproportionately high fraction of total stack cost.
The increase of efficiency and lifetime of stacks and Balance of Plant components directly serves the activities of SOLIDpower in addressing first niche markets and working towards lower cost and reliable residential micro-CHP systems.
The European fuel cell developers are increasingly coming under pressure from Japanese and USAmerican fuel cell system suppliers. The Japanese companies are already addressing the European market with systems that have been developed and subsidised in the NEDO demonstration programmes of the past years (some 220 000 of PEFC and SOFC residential FC systems sold and installed using an investment subsidy in Japsan). US company BloomEnergy is still limiting itself to the US market (for reason of high cost and high subsidies), whereas FuelCell Energy is still concentrating on MCFC deployment.
The EU still has a strong SOFC development basis and the use of the project results will further strengthen this. Seeing that the extension of lifetime may not be a main priority of the non-EU manufacturers who may be concentrating on lowering cost (e.g. by exchanging stacks after five years), EU companies may still profit from superior quality.
The research partners benefit from know-how generated that can be used in contract assignments with industry and further developments with the industrial consortium partners in projects or bilateral contracts.
Nevertheless, this situation will rapidly change with a measurable number of non-EU providers entering the market. It is therefore paramount to strengthen the EU companies in their technical capabilities (e.g. system durability and robustness, and especially cost). This also includes the many SME active in the field in Europe (e.g. SOLIDpower).
SCORED 2:0 directly contributed to these goals and offered a commercial opportunity for all project partners, including the research partners.
List of Websites:
Public website: www.scored-2-0.eu
Project contacts:
Co-ordinator Prof Dr Robert Steinberger-Wilckens r.steinbergerwilckens@bham.ac.uk
VTT: Johan Tallgren, Johan.Tallgren@vtt.fi
EPFL: Jan Van herle, Jan.Vanherle@epfl.ch
ENEA: Stefano Frangini, stefano.frangini@enea.it
MIBA/Teer Coating: Shicai Yang, shicai.yang@miba.com
TurboCoating: Francesco Bozza, francescobozza@turbocoating.it
SOLIDpower, Alessandro Dellai, alessandro.dellai@solidpower.com
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 the key contributions to the continuous performance degradation of SOFC devices that limits their lifetime. Stainless steel is generally used as interconnect (IC) material and chromium evaporating from these high chromium steels deposits within the cathode leading to formation of chromia and chromium spinels (depending on cathode materials). These lead to blocking of pores, reduction of electrical conductivity, and deactivation of the cathode material resulting in continuous degradation of performance. This form of degradation has been shown to be one of the main causes to be overcome to equip SOFC for stationary applications, which essentially require ten years of operational lifetime. In addition to the cathode poisoning problem, corrosion issues on the IC material itself also negatively affect the electrode-interconnect contacting in that the electrical resistance increases, thereby contributing to reduced 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 the market whilst avoiding chromium poisoning and corrosion issues.
The SCoReD 2:0 project, running from 2013 to 2017, aimed 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). It directly addressed the topics of reliability, durability and cost effectiveness for components used in SOFC stack and Balance of Plant manufacture.
The focus of SCoReD 2:0 was on choosing optimised combinations of protective layer materials with different steel qualities (including low-cost options) and coating processes, 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 were 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), atmospheric plasma spraying (APS), physical vapour deposition (PVD), and atomic layer deposition (ALD) methods. Coated steel samples were provided for standard tests of high temperature oxidation (exposure), area specific resistance (ASR), chromium evaporation, and bulk conductivity followed by post-test analysis of the tested samples. The best layer deposition processes were then selected 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 prototype SOFC stacks were successfully conducted to demonstrate stack lifetime of over 10,000 hours and industrial mass production cost reduction for the processes applied. A model was 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 were proposed for life-time prediction towards 10 to 15 years of operation (stack and system, respectively) with coated interconnects.
Project Outcomes
The proof-of-concept was performed on two stacks with 6 layers each, one of which operated for over 11,000 h within the project duration.
The benchmark of an ASR of 5 mΩ cm2 combined with a chromium diffusion of less than 1 weight% into the LSC material was accomplished by several powder applications by APS and PVD methods on all types of steel. Lower values were even obtained on the Sanergy HT and CroFer H steels. WPS application with MCFC powders came close. Samples with pre-nitriding achieved values below 20 mΩ cm2 but delivered more consistent results in the stack tests with negligible differences between individual layer performance.
The Lucerne SOFC Forum 2016 saw a high number of contributions from this project. The project partners delivered 35 journal papers, conference papers and conference contributions (talks and posters) to disseminate the project results. Exploitation will be performed by the companies involved in their day-to-day business and by the universities in their continued research activities.
Summary Conclusions
The Scored 2:0 project has demonstrated the possibility of using low-cost ferritic stainless steels such as K41 and 441 in combination with different coatings and deposition techniques.
Lab scale tests allowed to evaluate several interesting technologies such as ALD or Dip coating in molten salts but did not allow the application on real interconnects due to the small size of the reactors.
The technologies resulted to be viable for coating real interconnects are:
- Spray coating (SOLIDpower),
- Plasma spray (Turbocoating),
- Magnetron sputtering (Teer Coating Limited).
The results obtained from the project show that, despite the porosity of coatings obtained through wet chemical methods, the degradation observed over long-term stack tests is almost comparable to that obtained by PVD / CVD methods. Most likely the effect of a dense coating obtained with PVD / CVD methods is more noticeable in terms of stack degradation after 30,000 hours or more.
Lower grade steels (K41/441) come very close to the higher grades (Sanergy HT and Crofer 22 H) and in some few cases performed better. Statistics would need to further prove the reliability of these statements. In any case it can be deducted that the lower grade steels require a physically sealing protective coating (APS & PVD) whereas the higher grade steels can also deliver excellent ASR values with WPS applied layers, if they are sufficiently densified.
Project Context and Objectives:
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 the key contributions to the continuous performance degradation of SOFC devices that limits their lifetime. Stainless steel is generally used as interconnect (IC) material and chromium evaporating from these high chromium steels deposits within the cathode leading to formation of chromia and chromium spinels (depending on cathode materials). These lead to blocking of pores, reduction of electrical conductivity, and deactivation of the cathode material resulting in continuous degradation of performance. This form of degradation has been shown to be one of the main causes to be overcome to equip SOFC for stationary applications, which essentially require ten years of operational lifetime. In addition to the cathode poisoning problem, corrosion issues on the IC material itself also negatively affect the electrode-interconnect contacting in that the electrical resistance increases, thereby contributing to reduced 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 the market whilst avoiding chromium poisoning and corrosion issues.
The SCoReD 2:0 project, running from 2013 to 2017, aimed 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). It directly addressed the topics of reliability, durability and cost effectiveness for components used in SOFC stack and Balance of Plant manufacture.
The focus of SCoReD 2:0 was on choosing optimised combinations of protective layer materials with different steel qualities (including low-cost options) and coating processes, 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 were 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), atmospheric plasma spraying (APS), physical vapour deposition (PVD), and atomic layer deposition (ALD) methods. Coated steel samples were provided for standard tests of high temperature oxidation (exposure), area specific resistance (ASR), chromium evaporation, and bulk conductivity followed by post-test analysis of the tested samples. The best layer deposition processes were then selected 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 prototype SOFC stacks were successfully conducted to demonstrate stack lifetime of over 10,000 hours and industrial mass production cost reduction for the processes applied. A model was 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 were proposed for life-time prediction towards 10 to 15 years of operation (stack and system, respectively) with coated interconnects.
More details of the full project report are found in the final report deliverable D8.4.
Project Results:
This project consisted of eight work packages (WPs) in total, including one WP dealing with the overall technical management and project coordination. Results of each WP carried out for the second period (01/01/2015 to 30/06/2017) are summarised as below. More details of the full project report are found in the final report deliverable D8.4 and in the full periodic report for P2.
WP 1 – Sample Supply
During the second period of the project, coating powders of manganese cobalt oxide (MCO) doped with iron (MCF, Gen 3) and iron and copper (MCFC, Gen 4) were applied. Metallic interconnect steel samples of different suppliers (K41/441, Sandvik Sanergy HT, and CroFer H) and size (100x100x0.2 mm3 and 10x10x1 mm3) were provided for the coatings. Powders were sourced from the commercial suppliers and to some limited extent (G4) synthesised within the project. The Gen 5 samples were prepared on the basis of surface nitrided samples prepared by Teer Coating Limited (TCL/MIBA) using MCF powders.
WP 2 - Coating Application Development (wet chemical methods)
ENEA, University of Birmingham (UBHAM), and SOFCPower (SPower) were responsible for coating steel samples using wet chemical methods such as dip coating, WPS coating, and inkjet printing which are favourable for mass production due to the simplicity and cost-effectiveness of the processes. Gen 3/4/5 samples were prepared by WPS/inkjet methods. ENEA applied their La/Fe perovskite surface treatment. The addition of copper as sintering aid to the WPS powders improved the performce by increased densification. On the other hand, dip coating was less successful and could not be proven on prototype stack parts due to the limited size of samples that could be treated.
WP 3 - Coating Application Development (plasma and thermal spray methods)
Turbocoating (TC) used plasma spray methods (APS) to prepare Gen 3/4/5 samples. These displayed the best performance in ex-situ testing and this technique was tested on several layers within the proof-of-concept stacks.
WP 4 - Coating Application Development (sputtering, PVD and CVD methods)
Teer Coating Limited (TCL) and VTT were responsible for coating steel interconnects using physical vapour deposition (PVD) and atomic layer deposition (ALD) methods, repsectively. The PVD coatings showed excellent behaviour whereas the ALD did not match up to expectations. PVD coatings were also trialled in the proof-of-concept stacks.
TCL introduced plasma nitriding of steel surfaces in Period 1 - this proved to be beneficial to contact resistance and was also included in stack tests. It proved to deliver more consistent properties of the interconnect coatings in the in-situ (stack) tests.
WP 5 - SOFC relevant Corrosion Testing and Accelerated Testing
VTT, UBHAM, ENEA, and EPFL performed tests on samples originating from WPs 2, 3, and 4 with different methods, including:
- High temperature exposure (700 °C, 1000 h) followed by post-test microscopy,
- High temperature electrical resistance (ASR) measurement (700 °C, 1000 h) followed by post test microscopy,
- High temperature chromium retention test (700 °C, 1000 h) followed by post-test microscopy,
- Adhesion tests at room temperature.
A standard exposure test apparatus was established, also available for an acceleration test varying humidity and temperature. In addition, a novel characterisation method was developed to test high temperature electrical resistance and chromium retention (Fig. 2). This method replicates the stack conditions and materials as closely as possible. A coated steel plate is in contact with a cathode (lanthanum strontium cobaltite: LSC) coated palladium plate. Cr diffusing from the steel and reacting with the cathode happen in an identical way as in a real SOFC stack in the contact areas. 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 consistently showed lower ASR values compared with the other samples.
WP 6 – Post-Test Analysis
EPFL, VTT, ENEA, TC, and UBHAM performed post-test analyses 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, 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 the benchmark choice at 5 mΩ cm2, with the TC (APS) and TCL (PVD) samples delivering equivalent or better performance.
WP 7 – Stacks proof of concept testing
Several stacks were built by SPOWER as proof-of-concept stacks and tested for several thousand hours, the longest running for 11,000 hours with limited degradation.
WP 8 – Management and Miscellaneous Activities
A multitude of meetings and TelCo's were held to map progress of the project and take the imminent decisions on the stack testing.
The Lucerne SOFC Forum 2016 saw a high number of contributions from this project.
Potential Impact:
The project was industrially oriented and targeted commercial exploitation as required by the FCH JU guidelines and calls.
The work in the project fell into two categories
- basic research and understanding of materials and processes, and
- industrially focussed development of processes.
In so far there were two strategies of dissemination:
- the usual proliferation of scientific results and insights via conference presentations and papers (see final section), journal papers etc., and
- the constrained dissemination of industrial confidential developments in order to protect the competitiveness and cutting edge technology development of the industrial partners.
The project struck a reasonable balance between the two with a firmly installed procedure of gaining permission to publish vis a vis the justified interests of the industrial partners in confidentiality.
Project results were presented at conferences, at workshops, and at the final project event.
In order to propagate the findings and advertise the successes, a number of workshop contributions (e.g. to the series of Bruges workshops on SOFC systems run annually by U B’ham, VTT and Research Centre Jülich within the EERA context) and conference papers (ECS SOFC symposia and Lucerne SOFC Forum events) were prepared.
The tables in Part A show the project related publications, conference contributions, and events.
Dissemination by other means
Type Date Lead responsible Comments
mail shot Jan 2016 UBHAM advertising the April 2016 workshop and disseminating project results
mail shot April 2016 UBHAM advertising the Lucerne 2016 session and any workshop outcomes, and disseminating project results
mail shot Jan 2017 UBHAM advertising the April 2017 workshop and disseminating final project results
recipients of mail shots would include the FCH JU members (IG and N.ERGHY) as well as the wider SOFC community (Europe, U.S.A. Asia) as reached by FCH JU mail-outs and own mailing lists.
Exploitation of project results
The results of the project will be
- viable for mass production and low-cost manufacturing
- provide evidence of realistic component life and maintenance cycle consistent with system life >10 years (subject to the verification methodology and lifetime models developed) and consistent with market acceptance requirements
Benchmarking figures for success verification include:
- allowing for fuel utilisations of >90% (as far as specific SOFC cells and stacks allow) based on passivation of steel interconnects and tolerance to extreme water content
- therefore allowing for high system efficiency (depending also on both the SOFC cell efficiency and the BoP parasitic losses)
- achievement of low cost manufacturing
- achievement of high system lifetime and low cost of maintenance by avoiding mid-term replacement of stack
- development of lifetime prediction models for steel parts for optimised lifetime engineering
The potential for commercially exploiting the project results is high considering the high value of the issues mentioned above to all SOFC developers and manufacturers.
Commercial exploitation is directly given through the current commercial activities of the three industry partners. The two coating companies can directly implement results in their processes and/or adopt new processes if proven superior (and commercially viable). The stack manufacturer will integrate successful materials combinations into their design and has a vital interest in lower cost steels since these constitute a overproportionately high fraction of total stack cost.
The increase of efficiency and lifetime of stacks and Balance of Plant components directly serves the activities of SOLIDpower in addressing first niche markets and working towards lower cost and reliable residential micro-CHP systems.
The European fuel cell developers are increasingly coming under pressure from Japanese and USAmerican fuel cell system suppliers. The Japanese companies are already addressing the European market with systems that have been developed and subsidised in the NEDO demonstration programmes of the past years (some 220 000 of PEFC and SOFC residential FC systems sold and installed using an investment subsidy in Japsan). US company BloomEnergy is still limiting itself to the US market (for reason of high cost and high subsidies), whereas FuelCell Energy is still concentrating on MCFC deployment.
The EU still has a strong SOFC development basis and the use of the project results will further strengthen this. Seeing that the extension of lifetime may not be a main priority of the non-EU manufacturers who may be concentrating on lowering cost (e.g. by exchanging stacks after five years), EU companies may still profit from superior quality.
The research partners benefit from know-how generated that can be used in contract assignments with industry and further developments with the industrial consortium partners in projects or bilateral contracts.
Nevertheless, this situation will rapidly change with a measurable number of non-EU providers entering the market. It is therefore paramount to strengthen the EU companies in their technical capabilities (e.g. system durability and robustness, and especially cost). This also includes the many SME active in the field in Europe (e.g. SOLIDpower).
SCORED 2:0 directly contributed to these goals and offered a commercial opportunity for all project partners, including the research partners.
List of Websites:
Public website: www.scored-2-0.eu
Project contacts:
Co-ordinator Prof Dr Robert Steinberger-Wilckens r.steinbergerwilckens@bham.ac.uk
VTT: Johan Tallgren, Johan.Tallgren@vtt.fi
EPFL: Jan Van herle, Jan.Vanherle@epfl.ch
ENEA: Stefano Frangini, stefano.frangini@enea.it
MIBA/Teer Coating: Shicai Yang, shicai.yang@miba.com
TurboCoating: Francesco Bozza, francescobozza@turbocoating.it
SOLIDpower, Alessandro Dellai, alessandro.dellai@solidpower.com