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Development of PEM Fuel Cell Stack Reference Test Procedures for Industry

Final Report Summary - STACKTEST (Development of PEM Fuel Cell Stack Reference Test Procedures for Industry)

Executive Summary:
Fuel cell systems are more and more reaching industrial product readiness. In applications such as uninterruptible power supply as well as combined heat and power generation products are already on the market, however still mostly subsidized by government programs. A good deal of these products is based on Polymer Electrolyte Membrane (PEM) Fuel Cell technology. The PEM fuel cell stack represents the key component in such systems.
The work carried out in this project aims at the development of harmonized, industrially relevant test procedures allowing an assessment of PEM fuel cell stacks with respect to:

• performance,
• endurance, and
• safety related issues.

The tests developed within this project have been written in a common format allowing sufficient flexibility to adopt specific requirements of fuel cell application oriented testing. Typical application areas identified for PEM fuel cells are vehicle propulsion where the fuel cell can act either as the prime mover or as an range extender, stationary applications such as combined heat and power generation (CHP), uninterruptible and backup power supply as well as portable power generators. It is evident that PEM fuel cell stacks are operated under significantly different operating conditions in each of these applications. Recommendation for operating conditions typical for those applications have been given.
Initially, the existing documents on PEM fuel cell testing and PEM fuel cell stack testing as well as proposals from the consortium have been collected, analysed and critically assessed with respect to potential relevance for industry and application. The results of this assessment have been documented in test matrices for performance, endurance, and safety testing.
The tests considered relevant during this exercise have been assessed further and - where appropriate - separated in test modules varying a single input parameter at a time while observing the reaction of key output parameters, and test programs forming a more complex series of individual test modules.
During the assessment, it became evident that the major part of test modules developed for performance testing are also suitable in test programs addressing endurance and safety related issues. Therefore, a common pool of Test Modules has been collected.
Draft versions of the test modules have been written in the revised harmonized test format. Topics common for all tests such as test bench set up, definitions, location of sensors and control parameters have been compiled in a master document for performance testing and safety testing respectively. After completing the definition of test modules, selected test programs have been drafted.
Test modules and subsequently test programs have been assigned to individual partners for experimental validation. In general, a two stage definition, validation and revision approach has been followed.
Key results of the project so far were:
• Assessment of the status in international standardization of PEM fuel cell testing.
• Provision of sample stacks to each partner to carry out experimental work.
• Definition and validation of 22 test modules in two iterations addressing performance, endurance, and safety related issues of PEM fuel cell stacks
• Definition and validation of nine test programs addressing performance, endurance, and safety related issues.

The methodology as well as the content of the Test Modules and test Programs defined has been discussed with an industrial advisory board consisting of members representing different application areas. Furthermore, Test Modules and test Programs have been provided to other FCH-JU R&D-projects. Feedback from the industrial advisory board as well as from other projects has been integrated in document revision.
The project results have been communicated in international workshops held within the project, through contributions to international and national conferences as well as through publications in peer reviewed scientific journals.
Final release versions of the documents have been written. The documents will be made publicly available once editing is completed and priority dates for publications have been secured.

Project Context and Objectives:
The overall objectives of the project are the definition and validation of industrially relevant generic test modules and application oriented test programs addressing performance, durability and safety as well as environmentally related issues in testing PEM fuel cell stacks.

The major objectives for the project are summarized as follows:
• Review the status of international standardization with respect to PEM fuel cell testing.
• Agree upon a methodology how to describe performance, endurance, and safety test for PEM fuel cells.
• Define generic Test Modules to be used for performance, endurance, and safety testing addressing the reaction of a PEM fuel cell stack to the variation of a single input parameter.
• Provide samples of Test programs addressing more complex test tasks
• Provide a methodology to carry out PEM fuel cell stack tests under application specific boundary conditions.
• Form an industrial advisory board providing user feedback to the project results.
• Disseminate the project results in stakeholder workshops.
• Disseminate the project results in conferences and scientific papers.

Project Results:
Summary of Achievements and Progress
In the course of the project the following progress with respect to prior activities has been achieved:

• The status of international standardization with respect to PEM fuel cell testing has been assessed at the beginning of the project. Annual updates have been provided.
• An industrial advisory board has been formed.
• A methodology to describe PEM fuel cell stack testing has been defined an agreed upon as a Master document TM P-00.
• Agreement has been found upon definitions such as sites of parameter control, stability criteria and test parameter nomenclature by all project partners to get reproducible results. Validation was performed within Round-Robin testing.
• Generic Test Modules addressing the reaction of a PEM fuel cell stack to the variation of a single input parameter to allow their use as building blocks for Test Programs have been defined.
• Test Modules have been defined and refined in a two stage process involving experimental validation, consultation with the industrial advisory board and discussion during dissemination workshops.
• Preparation of a one-page abstracts for each Test Module and Test Program to provide comprehensive information for use by experts.
• First approach of definitions to determine the degradation rate within a durability test
• Four stakeholder workshops have been held where project results have been disseminated. Feedback from the workshops has been integrated in the Test Modules and test Programs.
• Scientific papers derived from test results, partly already published
• Input for International Standardisation as a New Work Item Proposal submitted to IEC TC-105.

Functional and Performance Testing
Key achievements
• Definition and validation of test modules concerning sensitivity studies of different parameters in two iterations
• Reproducibility investigation of test results performed by different partners on different test benches using similar objects under test.
• Drafting and final validation of different test programs using the defined Test Modules.

Progress beyond the state of the art
• Definition of test modules and test programs on a stack level in a consistent manner
• Identification of critical parameter controls to assure comparable stack performance characterization

Endurance testing
Key achievements
• Drafting and validation of generic test modules and test programs:
• Steady-State
• Load cycling
• Start-Stop
• Performance Recovery
• Application specific adaption within the context of harmonisation efforts:
• Transforming the NEDC dynamic load cycle to a “Fuel Cell Dynamic Load Cycle (FC-DLC)” which can be performed on a broad range of fuel cell test benches.
• Definition of “test block”, containing a number of consecutive performed Fuel Cell Dynamic Load Cycles to perform degradation tests.
• Results led to a proposal of how to measure degradation rates
• Presentation of the results in a Brussels harmonization meeting
• Identifying of critical parameters during Start-Stop testing.
• Combination of the Test Modules “Start-Stop”, “Load Cycling” and “Performance Recovery” within a validated automotive durability Test Program.
• Adoption WP2- definitions to WP3: same nomenclature and naming of parameters
• Transmission of the drafted test-modules to other running European Projects

Progress beyond the state of the art
• Effort of transformation of the generic test-module “load cycling” to an application specific test-module was successful.
• Broad acceptance within the project partners, good feedback from industry.
• Drafted test-modules and test-programs are (in combination of WP2-drafts) basic documents for planning of endurance tests in other running European projects.

Safety testing
Key achievements
• Selection, definition and validation of stack relevant safety tests.
• Drafting of safety related test-modules and test programs, based on the common standard IEC 62282-2 (Fuel Cell Modules), which gives only a framework of safety-tests.
• Giving detailed test descriptions and examples beyond the general requirement of performing “according to manufacturer’s recommendation”.
• Identification of existing experimental challenges (e.g. sample rate during short circuit test)

Progress beyond the state of the art
• Detailed description and validation of tests required for type approval by the IEC stack-standard by giving examples of validation experiments:
• Description of test equipment,
• Description of minimum requirements for test infrastructure,
• Detailed declaration of test input and test output parameters.
• Adaptation of shaker test from battery testing and giving recommendations of how to gather additional information regarding mechanical stiffness by performing of resonance sweep tests.

Detailed Description of Achievements and Progress

The work carried out within the project Stack-Test has been based on previous work done within the FP6 project FCTESTNET, FCTESQA, and FCTEDI. In these projects a general methodology for fuel cell testing has been developed and validated at a single cell as well as a system level. Stack level testing of PEM fuel cells, however, has not been covered fully in these previous projects.
The overall objective of this work is to continue the line of work started in the FP6 projects and develop and experimentally validate test procedures specifically for PEM fuel cell stacks addressing performance, endurance, and safety related issues. Furthermore, a review of international standardization activities related to PEM fuel cell testing shall be given and kept updated during the course of the project. Liaison with standard developing organizations as well as industrial stakeholders shall be established.
Initially, the methodology describing fuel cell testing developed in the previous FP6 projects as well as the harmonized format describing the tests has been reviewed with respect to applicability, ease of use and potential industrial relevance for testing PEM fuel cell stack performance, endurance, safety, and environmental issues.

Review of the Methodology
The general methodology describing PEM fuel cell testing based on generic test modules in which the reaction of stack output parameters (e.g. voltage) to the variation of a single stack input parameter (e.g. current) while keeping the other input parameters constant has been adopted also for stack testing.
Nevertheless, it has to be noted that unlike in single cell testing not all input parameters can be varied independently. In stack testing, the variation of the one input parameter (e.g. current) is likely to cause variations of other input parameters (e.g. gas flow, pressure drop, temperature spread etc.) as well. Therefore, it is necessary to carefully record and report all variations in in- and output parameters when carrying out stack testing. A precise definition where parameters such as stack temperature, pressure humidity are measured and controlled is essential.
Besides the review of the test procedures available from FCTESTNET and FCTESQA, the harmonized format for describing and reporting tests has also been reviewed. Based on experiences in the various laboratories, a simplified format has been developed. Furthermore, common issues to all test modules such as test bench quality and stability criteria, frequently used procedures etc. have been collected in a master document.

The test module description as used in FCTESTNET and FCTESQA has been updated to allow for flexibility in the definition of input parameters in order to cover application specific requirements. Recommended sets of input parameters characteristic for different applications are under development.
More complex tasks have been organized in test programs of individual test modules arranged in a series or loop structure. Such a sequence can be designed representative for different applications taking into account the different dynamic and lifetime requirements encountered in applications such as automotive propulsion, CHP or portable power generators.
Organization of PEM fuel cell tests in generic test modules and application oriented test programs thus provide great flexibility in designing application relevant tests as well as providing fundamental information on the stack operating characteristics.
All test modules and test programs developed in this project have been written using the updated description and reporting format.

Definition of generic PEM fuel cell stack test modules
Based on an initial compilation, 22 test modules have been selected as specific and relevant for PEM fuel cell stack testing. After writing up the details and further review, 17 of these test modules have been selected for experimental validation.
The test modules considered most important are being validated by all partners. Other test modules will be validated by a minimum of two partners by the end of the project.

Generic Test modules relevant for PEM fuel cell stack testing
Module Title
TM P-00 Stack Test Master Document
TM P-01 Humidity Sensitivity
TM P-02 Temperature Sensitivity
TM P-03 Pressure Sensitivity
TM P-04 Stoichiometry Sensitivity
TM P-05 Fuel and Oxidant Composition
TM-P06 Low Temperature Test
TM P-07 Continuous Operation at Constant Load
TM P-08 Polarization Curve
TM P-09 Impact of Stack Tilt
TM P-10a Electrochemical Method: Voltammetry
TM P-10b Electrochemical Method: Potentiometry
TM P-10c Electrochemical Method: Impedance Spectroscopy
TM P-10d Electrochemical Method: Hydrogen Crossover
TM P-10e Electrochemical Method: Methanol Crossover
TM P-11 Dead-End Operating Conditions
TM D-01 Constant Load Durability
TM D-02 Load Cycling
TM D-03 Start-Stop Durability
TM D-04 Stack Performance Recovery
TM S-01 Gas Leakage Test
TM S-02 Vibration Test
TM S-03 Pressure Stability Test
TM S-04 Freeze-Thaw-Cycling Test
TM S-05 Excess Temperature Test
TM S-06 Short Time Rated Current
TM S-07 Dielectric Strength
TM S-08 Short Circuit Test

The project achieved its objective of selecting and validating industrially relevant test modules. Lessons learned and shortcomings identified during the first reporting period have been used for revision and subsequent successful validation of the test modules in the second reporting period.

Definition of application oriented PEM fuel cell stack test programs
A series of application oriented test programs addressing performance, endurance, and safety aspects have been drafted and validated.

Test Programs relevant for PEM fuel cell stack testing
Module Title
TP P-01 Stack Performance Assessment
TP P-02 Stack Performance Mapping
TP P-03 Deviant Stack Performance
TP P-04 Dead-End Performance
TP P-05 Stack Performance Optimization
TP D-01 Durability
TP S-01 Mechanical Safety Analysis
TP S-02 Temperature Safety Analysis
TP S-03 Electrical Safety Analysis

Intense discussions at the beginning of the project led to the approach to cover application specific differences in test conditions for performance and endurance testing by representative Test Input Parameters (TIP). This approach allows sufficient flexibility to use the test modules while simultaneously providing guidelines to take application specific differences as they are known today into account. This approach has been discussed with the industrial advisory board. Table 3 gives a recommendation for application specific Test Input parameters.

Application specific reperesentive Test Input Parameters (TIP)
Parameter Automotive Stationary Portable Generators
Name Symbol Propulsion (I) Propulsion (II) Range Extender. APU CHP Backup Hydrogen DMFC
Stack Temperature (Coolant inlet) TStack 80 °C 68 °C 75 °C 75 °C 70 °C 65 °C 50 °C 70 °C
Reactant inlet temperature Tgas,in 85 °C 73 °C 80 °C 80 °C 75 °C 70 °C Ambient Ambient
Fuel (H2) stoichiometry λfuel 1.3 1.4 1.5 1.5 1.2 1.25 1.2 5.0
Oxidant (air) stoichiometry λOx 1.5 1.6 2 2.0 2.0 2 2 2.5
Fuel relative humidity RHfuel 50% 40% 80% 80% 80% 40% 50% -
Dew point temperature fuel DPfuel 63.5 °C 48.2°C 69.5 °C 69.5 °C 65 °C 45.5 °C 36.5 °C -
Oxidant relative humidity RHox 30% 50% 80% 80% 80% 40% Ambient Ambient
Dew point temperature oxidant DPox 52.5 °C 52.5 °C 69.5 °C 69.5 °C 65 °C 45.5 °C Ambient Ambient
Fuel outlet pressure Pfuel 220 kPaabs 220 kPaabs 150 kPaabs 150 kPaabs Ambient 120 kPaabs 150 kPaabs Ambient
Oxidant outlet pressure Pox 200 kPaabs 200 kPaabs 150 kPaabs 150 kPaabs Ambient Ambient Ambient ambient

Two different sets of TIPs have been adopted representing most likely future vehicle operating conditions (Propulsion (I)) at elevated temperature and reduced humidity. These conditions are harmonized with the current definition of harmonized test reference conditions for single cell testing. Obvious differences in pressure levels are originating from pressure control positions. While Stack-test recommends control of stack pressure at the exit, the harmonized European test conditions ask for pressure control at the cell inlet. TIPs defined in Propulsion (II) are more representative for state of the art vehicle operating conditions.

Review of international standards related to PEM fuel cell stack testing and liaison to standard developing organizations
Existing international standards are having substantial influence on different aspects of fuel cell testing. As a consequence, test modules and test programs are developed in the different work packages keeping in mind the existing standards and tests procedures elaborated all around the world. Following a review and a first update on the status of international standardization relevant for PEM fuel cell stack testing carried out in the first reporting period, a second update has been compiled.
Procedures and program tests can be found from the following documents:
• U.S. DRIVE Partnership Fuel Cell Technical Team [5]
• JIS C8832: performance test for stationary polymer electrolyte fuel cell stack [6]
• FCTESQA: procedures dedicated to fuel cell stack characterisations [7]–[11]
• IEC 62282-2:2012: International standard providing minimum requirements for safety and performance of fuel cell modules in all applications [12]
• SAE J 2617 : SURFACE VEHICLE RECOMMENDED PRACTICE: Recommended Practice for Testing Performance of PEM Fuel Cell Stack Sub-system for Automotive Applications [4]
• SAE J 2615 : SURFACE VEHICLE RECOMMENDED PRACTICE: Testing Performance of Fuel Cell Systems for Automotive Applications [13]
• European Commission (2006) The Fuel Cells Testing & Standardisation Network, FCTESTNET : Fuel cells glossary [14]
• IEC/TS 62282-1:2013 Fuel cell technologies - Part 1: Terminology [15]
• IEC 62282-6-100 :2010 [16]
• GL guideline (2002): (VI-3-11) Guidelines for the Use of Fuel Cell Systems on Board of Ships and Boats [17]
Additional information can be extracted from the fuel cells standards website [18]. Some national relevant procedures which are not available in English language (e.g. Chinese) have not been taken into account in this document.
A summary of the contents of these documents can be found in the corresponding deliverables.
Members of the consortium are active in relevant standardization committees on IEC and ISO level. The work carried out in the project has been used as the basis of a new work item proposal on PEM fuel cell stack testing to the IEC TC-105. It has been suggested to treat this as part of the fuel cell module standard (IEC 62282-2).
An industrial advisory group with representatives from relevant application areas has been formed. A joint meeting has been held during the first general assembly in October 2013.

Specification and manufacturing of sample stacks for experimental validation.
Partners active in experimental validation of test modules and test programs have been supplied with sample stacks using graphitic bipolar plates from ZSW and stacks using metallic bipolar plates from CEA. The stack technologies chosen are representing CHP / portable power generation (100 cm2 graphitic bipolar plates) and automotive (220 cm2 metallic bipolar plates) applications respectively.
The stacks and reference operating conditions have been jointly specified. All partners active in experimental validation have been supplied with one graphitic and one metallic stack by end of 2013. The stack performance at begin of life was consistent with the current state of the art of commercial MEA and BPP technology. Stack performance was homogeneous within less than 20 mV at a current density of 1 A/cm-2.

Potential Impact:
The developed procedures for performance, durability and safety testing are prepared and validated in a consistent manner and can be used in industry for quality management for stack manufacturing and for stack benchmarking by system integrators with respect to the specifications of the system and the application. By the use of the test procedures with defined Test Operating Conditions, the tests of different stack manufacturers may become comparable and allow the assessment of stack performance, endurance and safety without additional test series by each system integrator.
Furthermore, the test procedures provide a common basis to be used in research projects on PEM fuel cell stacks in order to validate the respective development in each project and compare the results among different projects. Consequently, the key achievements within a project can be reliably assessed.
Test Modules and test Programs have been communicated to other FCH-JU projects where they have been used as a basis for stack related test tasks.
The project provided a New Work Item Proposal to the IEC TC-105 for performance testing of PEM fuel cell stacks. If accepted, the project results can be carried over to an international platform. Furthermore, regular maintenance is part of international standardization to take future development and findings in PEM fuel cell testing into account.
In general, the successful development of harmonised test procedures for PEMFC stacks within Stack-Test can support and accelerate the development of stack components and the improvement of the stack design. Thereby, the introduction of this technology to the market can be supported for the different applications.

List of Websites:
Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg
Ludwig Jörissen
Helmholtzstr. 8
D-89081 Ulm, Germany
Tel.: +49-731-9531-605

Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg
Jürgen Hunger
Helmholtzstr. 8
D-89081 Ulm, Germany
Tel.: +49-731-9530-831