COatings for BipolaR plAtes

Periodic Report Summary 1 - COBRA (COatings for BipolaR plAtes)

Project Context and Objectives: COBRA, consortium of European industrials and scientists, has been initiated to study new manufacturing methods and coating concepts for metal bipolar plates and demonstrate their interest for Fuel cell systems in real life conditions. 

Project Context and Objectives:

COBRA, consortium of European industrials and scientists, has been initiated to study new manufacturing methods and coating concepts for metal bipolar plates and demonstrate their interest for Fuel cell systems in real life conditions.

The bipolar plate is presently, by weight, volume and cost, one of the most significant components of a fuel cell stack. Bipolar plates can be made from various materials with the most common ones being graphite, metal, carbon/carbon and carbon/polymer composites.

However, from the automotive OEM’s point of view, two main targets are mandatory for the vitality of the fuel cell vehicle market: fuel cell stack and system compactness (<2kW/kg and <2kW/L) and fuel cell system cost (<50€/kW for 500000 fuel cell systems per year).

The only way to reach these targets is to use metallic bipolar plate for automotive fuel cell stacks and most of the automotive OEM’s have already chosen this technological option. The higher strength of metallic bipolar plates allows for higher power density stacks, which is desirable especially for transportation applications. Furthermore, metallic plates have a low thermal mass and high thermal conductivity, which is particularly beneficial for efficient cooling and rapid start-up. However, while metallic plate can have excellent electrical bulk conductivity and be produced via inexpensive manufacturing methods, a major drawback is often the need for a corrosion resistant conductive coating: any manufacturing technologies and new coating for bipolar plates should be consistent with the objective cost targets.

COBRA aims a competitive metallic bipolar plate solution that can be accessed and shared by several OEM’s for their individual system integration work and mobility platforms.

The COBRA project represents a mature approach towards reaching the technical and commercial targets of bipolar plates for automotive stack development based on the 2013 AIP targets. The COBRA project is providing the following specific benefits:

- Bipolar plate specifications based on agreed OEM system requirements;

- Strong production know-how of industrial partners;

- Performance and durability objectives compatible with the stringent requirements of the automotive industry;

- Post-mortem studies, phenomena modeling and ageing simulation to allow complete understanding of the technology;

- Tests operated in real conditions and verified in detail on component, cell, and stack level by highly skilled research institutes and industrial partners;

- Marine and automotive conditions demonstrated on-field with operating fuel cell systems.

The strength of COBRA project is having a clear and result oriented, technical workflow:

- Reference tests with classic bipolar plate coating, operated in automotive and marine conditions (WP2)

- Post-mortem analysis of aged plates and aged MEA (WP3)

- Characterization and modeling of the bipolar pates and MEA in aggressive environment (WP4)

- Definition of dedicated test protocols to be used in the development of COBRA project (WP5)

- Development of new innovative coating for bipolar plates (WP6)

- Production and validation of prototype plates issued of previous works (WP7)

- Field tests of prototype plates (WP8)

COBRA is moreover benchmarking innovative processes and component solutions to further reduce bipolar plate and stack cost. The technical development is accompanied by a detailed cost analysis using tools established for the industry involved in mobility.

The COBRA scheduled work plan comprises activities related to the complete understanding of the market and commercialization of bipolar plates as well as creating the conditions of industrial utilization of the results of the project by the consortium members. Dissemination efforts are therefore included in the project to present COBRA bipolar plate solution as a European response to the global fuel cell technology progress.

The COBRA Project has been funded under Fuel Cell and Hydrogen Joint Undertaking. The Project has started the 1st of April of 2014 and it will last for 36 months.

Project Results:

The COBRA project is at month 18. Lots of progress has been done in the understanding, testing and the modeling of the corrosion phenomenon, as well as on the definition and characterization of new coatings.

During the first 18 months of the COBRA Project, the work corresponding to WP1, WP2, WP3, WP4, WP5, WP6, WP7 and WP10 for this period have been done, as planned in Annex I. Complete work and main events that occurred during the project are described hereafter. Issues have been faced on the components production and the field tests parts of the project respectively, resulting in minor deviations that are explained in the present document.

In work package 2, all partners of the consortium have worked to have reference bipolar plates assembled in a stack, then tested in automotive and marine conditions.

A total set of 300 bipolar plates, using reference coating, were formed and coated with Au PVD process. Two stacks were produced using commercial plates and COBRA plates, to be tested in Zero-CO2 lab-boat and Symbio FCell range extender system.

Using sample material and sample plates without sealing, reference Au PVD coating behavior was tested and characterized in different mediums and with different electrochemical approaches. Moreover, their morphology and ICR were analyzed. The obtained results allowed to confirm that the Au PVD gold coating fulfill most of the COBRA project criteria. However, its main drawback is its price that prevents it to be used in transport field. It is thus a good performance reference.

Tests were performed in both maritime environments (6 weeks mission in south of France and west coast of Italy) and automotive environment (500hrs in Symbio FCell system conditions) with these reference gold coated plates. Average ageing obtained were -30µV/hr for automotive tests and -500µV/hr for maritime tests. These results will be used as reference for future tests planned in WP8.

INSA, IK4-CIDETEC and CEA expertize of BP and MEA, done during work package 3, permits to highlight and identify several points of improvement in terms of coating process.

• The first one concerns the stainless steel conditioning before coating elaboration. This step will prevent the growth of defects. Surface preparation is important but the conditions of elaboration could be contribute from respecting Thornton diagram.

• The second point implies the respect of topography of bipolar plate to cover perfectly the channels. This point could be performed considering motion during the deposit process.

• The third point focuses on the welding process. We observe the most important defect on the welding part. That should induce an important phase of welding optimization.

The obtain results allowed confirming that the corrosion of BP is due to growth defect, morphology of coatings in the channel and coating growth on the welding zone. Each of this point has to be improved to limit corrosion under coating due to galvanic corrosion.

In work package 4, the release of cationic pollutants from metallic bipolar plates during PEMFC operation were studied by IK4-CIDETEC and CEA.

These ions can significantly decrease PEMFC performance, because of their interaction with the membrane and the catalyst layers. With regards to the membrane, cations showed stronger affinity than H+ with the sulfonic acid group in PFSA membranes. When the fuel cell was operating, more active sites were occupied by the multivalent ions and, as a consequence, the membrane bulk properties, such as membrane ionic conductivity, water content, and H+ transference numbers, changed proportionally to the cation ionic charge, reducing the cell performance. So, it is necessary to provide method of the membrane regeneration, which will depend on the nature of the cationic pollutant. Relating to the catalyst layers, the presence of pollutant ions at the interface between the catalyst (Pt) and the ionomer causes specific changes that could be due to metal ion reduction or monolayer metal deposition reactions, which ultimately affects the kinetics of the processes taking place at the electrodes. This would be the case of Fe3+ on the oxygen reduction reaction. Despite this effect has been reported in the literature, some issues, like the influence of the ionomer, the dependence of kinetic current of ORR on different levels of cationic contamination in solution, or the adsorption or not of cations, indicate that the exact mechanisms of cationic contamination have yet been fully explained.

Furthermore, several models in terms of membrane and cathode contamination have been proposed, which to some extent account for the loss of performance degradation of the PEMFC due to cation contamination, but improvements related to the pH gradient in the presence of contaminants, when current is flowing in the cell, are still needed to improve their accuracy. In addition, it is necessary to validate models by experimental work. In this way, it will be possible to give recommendations on materials selection for bipolar plates.

Thus, in WP4 the work performed, regarding the evaluation of the effect of the contaminants released by bipolar plates on the performance of PEMFC, have been done at two levels: MEA and components (membrane and catalyst layers). Specific experiments have been designed to study the mechanisms of performance degradation due to cationic contamination. Furthermore, a model has been proposed to better understand the effect of the cationic contamination on the PEMFC. The main results achieved so far are:

• Identification of cationic contaminants released by the bipolar plates.

• Protocol definition to assess the impact of Fe2+ cationic contaminant on catalyst layers ex situ (in liquid electrolyte) and in situ (MEA).

• Studies of potential contamination level of Fe2+ cationic contaminant in operating conditions relevant to the applications envisaged in COBRA project.

• Development of a 2D +1 D fuel cell model in the Matlab/Simulink environment (MEA module + bipolar plate sub-module) for reference calculations without consider degradation, regarding the marine application in Zero CO2 sail boat.

• Development of model for membrane degradation, regarding the marine application in ZeroCO2 sail boat.

• Qualitative estimation of the local evolution of the membrane thickness when bipolar plate oxidation takes place.

As the project is dedicated to bipolar plate improvement, work package 5 was focused on defining tests to evaluate bipolar plate’s performance and endurance. Using Stacktest (FCH-JU project) findings and real life solicitation coming from ZeroCO2 tests and automotive tests performed in COBRA project, CEA, IMPACT COATINGS, SYMBIO FCELL and INSA defined and discussed several performance tests and durability tests.

• Two different types of stack performance procedures were define during this task: polarization curves and impedance tests.

• In-situ tests were also described to be used during mini-stack tests.

• Durability tests, taken into account classic OEM, ZeroCO2 Lab-boat and Symbio Fcell solicitation, were defined

• All the tests were integrated into a complete test procedure to be used in WP7.

In work package 6, CEA, BORIT, IMPACT COATINGS, IK4-CIDETEC and INSA have worked in the development of protective coatings, using three different approaches:

• Application of sol-gel coatings based on silanes doped with different additives for enhancing their conductivity.

• Gold, Silver and Nickel coatings obtained by electrodeposition.

• Ceramic MaxPhaseTM, TiC-based and NbC-based coatings obtained by PVD.

The developed sol-gel coatings showed very good corrosion behavior, even better than gold coatings obtained by PVD. The ICR values of the developed sol-gel coatings were higher than the target of the project but the addition of metals and carbon nanotubes decreased this parameter considerably. Currently the sol-gel layers with Cu and graphite are being characterized. Once all the corrosion and ICR results will be completely analyzed, the optimization of the coatings will be carried out and the combination of metallic and sol-gel coatings will be studied.

Metallic coatings led to low ICR values, fulfilling the established target of the project. Electrodeposited gold also showed good protective properties and its corrosion performance was similar to the one of gold coatings obtained by PVD. Moreover, lower thickness (2 µm) of electrodeposited gold led to the same results, so a study is being carried out in order to get the minimum thickness required to maintain the anticorrosive and conductivity characteristics of the layer at most competitive cost. However, the corrosion properties of nickel and silver coatings did not reach the required values.

Au PVD coating and Ti-C experimental fulfill most of the COBRA project criteria. Ceramic MaxPhaseTM almost fulfills most of COBRA project criterion but it is sensitive to small potential variations in oxygenated medium. TiC-based and NbC-based coatings were optimized with respect to contact resistance, which was in the same order than Au PVD coatings. The NbC-based coatings failed in the ex situ corrosion test, while the TiC-based coatings exhibited an increase from about 20 mohm to 35 mohm after 24 h test.

In Work package 7, CEA, BORIT, IMPACT COATINGS, IK4-CIDETEC and INSA achieved the first step of the realization of the sample bipolar plates using new COBRA technology and process: the workflow used to produce the plates in WP2 was used as the reference workflow that is described in detail to allow production. Also the production of the bipolar plates using new coating has been defined and they will be produced accordingly to project planning.

As soon as the plate’s production is completed, the plates will be tested in mini-stack using WP5 complete test procedure to qualify the performance and ageing of COBRA plates.

Work package 8 and 9 have not started yet, but the realization of the new field tests and the cost analysis study are being prepared already.

The activities on “exploitation and dissemination” of work package 10 were mainly focused on the implementation of the dissemination strategy.

All the actions required to present the project within the scientific and industrial community have been undertaken. A project website has been prepared and it is continuously updated; a non-confidential presentation, to present the COBRA project, has been prepared and shared. Besides, various contributions have been presented to various international conferences presenting and discussing results achieved in the COBRA project. The first version of the Plan for use and dissemination of foreground has been prepared.

Finally, cross work with project STAMPEM was initiated: COBRA participated in a STAMPEM workshop in October 2014 in Birmingham (England) to participate to stack tests definition; a first workshop was co-organized with STAMPEM project in May 2015 in Sattledt (Austria) to create links with other projects and R&D organizations working in the bipolar plates coating field. During this workshop, decision was taken to continue to strengthen the coating community by organizing a workshop in the Alps in late 2016 or beginning of 2017, to share advanced COBRA results.

Potential Impact:

In 2014, the fuel cell industry grew by almost $1 billion, reaching $2.2 billion in sales, up from $1.3 billion in 2013. Major increases were seen in North America and Asia Pacific revenues, spurred by fuel cells for material handling and large-scale stationary sales by U.S. companies and residential fuel cells in Japan.

In 2015, with Hyundai Tucson fuel cell and Toyota Mirai, the first commercial fuel cell vehicles were launched on the automotive market. Those are still expensive and low volume but the availability of fuel cell technology for the customer is now a reality.

In Europe, demonstration projects funded by FCH-JU, as well as national initiatives, are helping the introduction of fuel cell, notably concerning the mobility: project HyFive, HyTec or CHIC presents impressive objectives and achievements.

The COBRA consortium has the objective to strengthen European competitiveness by coordinating and combining critical fuel cell component and stack developments activities at European level. It will help implementing the stack concept developed in previous FCH-JU project such as Auto-Stack and Auto-stackCore projects, based on joined OEM specifications of major European automotive OEMs, by offering a full European bipolar plates solution.

The following three major pillars will allow this technological availability:

• The demonstration of a full alternative and innovative production concept for metallic bipolar plates devoted to transportation with high level of performance and durability;

• The validation of the COBRA process at stack and integrated system level;

• The demonstration of the economic feasibility of the COBRA process.

COBRA project is dedicated to the commercialization of fuel cell components and stack with highly implicated partners. As an example, Symbio FCell has produced and delivered around 200 vehicles with fuel cell range-extender (with 50 vehicles for HyFive project) and is planning up to 1000 vehicles in 2016. Impact Coating has also announced different partnerships with OEM, including Symbio FCell.

List of Websites:

http://www.cobra-fuelcell.eu/