Control Strategies and Test Protocols for Reliable and Comparable PEMFC Stack Benchmarking

Kurzfassung

Polymer electrolyte membrane fuel cell (PEMFC) systems are one of the most effective and promising power systems because they provide high fuel-to-electricity conversion efficiency and low to zero emission. However, several challenges need to be overcome for the commercialization of this technology. Apart from the costs, the main challenges are stack performance and durability. Both aspects are under evaluation in many laboratories with the aim to optimize the stack components and the stack design and to benchmark available stack platforms. The reliability of these results is thereby crucial. Many parameters have significant impact and may vary using different test hardware and test procedures. For stack characterization, parameter gradients across the stack, such as for temperature and pressure, have to be considered additionally. Consequently, the use of standardized procedures as well as clear definitions of the control strategies during test and of all used sensors are highly important for the reliable comparison of the test results and for the acceleration of stack development. These definitions are not consistent or not included in existing procedures and standards. The EU-funded project Stack-Test was initiated to create test reference procedures to assure reliable benchmarking of different stacks. The benchmark results can be used to identify the best stack design for a certain application. The presentation summarizes the outcome of the project and points out the requirements for reliable and comparable characterization of stack performance and durability. For the definition of reliable test protocols, already existing definitions by IEC, JIS and SAE were taken into account and were analyzed regarding consistency and missing definitions. Consistency was adopted and missing definitions and objectives were added. The test methodology defined by Stack-Test is a modular approach consisting of Test Modules (TM) and Test Programs (TP) for 3 objectives: (i) functional and performance, (ii) durability and endurance, and (iii) environmental and safety. The TMs are generic modules applicable to all PEMFC applications. One single test input parameter is varied while the impact on different test output parameters is determined. The TPs are application specific and combine the prepared TMs to a TP. In general, all TMs can be combined in a free manner to cover a certain test objective. All test procedures were validated by several research institutions across Europe and the final procedures are available at the project website. Selected examples of the prepared test protocols regarding performance and durability are demonstrated and test results using different 10-cell short stacks are presented in this presentation. The possibilities for the positioning of the parameter control sensors and for the parameters variation in sensitivity tests are also discussed. Recommendations for the resulting control strategy are given based on these discussions and considering general safety, stack safety, parameter stability, test duration, and comparability to an operating fuel cell system. Finally, test operating conditions (TOCs) for benchmark tests for different applications are summarized to enable the comparison of research achievements, even if these conditions do not totally match the conditions in the target system. The presented achievements by the Stack-Test project overcome an existing lack of definitions needed for reliable and comparable PEMFC stack performance characterization. Consequently, the developed benchmark methodology can be a powerful tool for system integrators to identify the best stack for a certain application, for stack manufacturers for quality assurance and for stack development, and for academia to assure reliable comparison of research results.