The aim of the DECODE project is to elucidate degradation mechanisms in PEFC with special focus on the influence of liquid water and in a second phase to modify components to achieve a significant improvement of PEFC durability. The focus of the project is the creation of new knowledge and understanding of the PEFC degradation processes, and in addition, the practical improvements of fuel cell performance and durability.
The project encompasses 11 partners with the necessary and important expertise to investigate and quantify degradation related phenomena in fuel cells and to derive strategies for improved durability.In particular, the project profits from the inputs of two car and truck manufacturers, component manufacturers, research institutes with their advanced testing infrastructure and universities with advanced modelling expertise. The project is structured into 7 work packages for the investigation of various components of PEFC and in the field of organization and dissemination (involvement of all partners). The work packages are shortly described at the end of the summary. DECODE focuses both on detailed component characterisation and also subsystem (short stack) testing and analysis. The project aims at deriving the maximum information from all testing and analytical work but also follows a pragmatic approach. If specific component information can only be derived from a specific model configuration it is accepted within DECODE that the simplified arrangement is used. On the other hand, components are tested in long-term operation in short stacks under realistic and technical conditions thereby leading to naturally aged components. These will be analysed with all available analytical tools within the framework of the project. The components of PEFC investigated in the project consist in the electrodes, membranes, diffusion media and bipolar stacks. In-situ and ex-situ analysis is performed leading ideally to preliminary life time predictions at the end of the project. A special strength of the project is the large modelling activity which is expected to significantly advance knowledge and understanding of the processes leading to degradation and also to deliver the tools to describe ageing and performance degradation.
Progress of work since start of the project
According to the project plan the specification phase is be terminated at this point, but it is clear to all partners that modifications to these specifications may be necessary in the future with knowledge gain and shifting focus from understanding to improvement. Therefore updates of the specifications will be necessary and will be reported in future.
For all components state-of-the-art reviews (reports) are being prepared to have a solid knowledge base from literature to derive the strategies for the improvement phase where strategies to incorporate durability gains are derived. Due to the delayed start of the project but also by the size and extension of the available literature on this topic with many ramifications the reports have been delayed significantly. Most or the reports are available in the final state and no significant impact of the delayed on the project success is expected from the delayed deliveries. The reports on the state-of-the-art will be made public by peer reviewed publications of the project in a suitable journal. For this peer reviewed publications the content of the deliverables combined D3.1 and D3.2 related to the degradation of CCM, D4.1 (degradation of GDL) and D5.1 (degradation of bipolar plates) will be used as base.
The first focus of the membrane and electrode activities has been the definition of the CCM material based and the testing procedures to ascertain a good comparability and successful testing in all laboratories. This work which has been mainly preformed in collaboration between CEA and Solexis yielded first ageing results of differently prepared CCM but – more important- defined the reproducible material basis for further investigation at all DECODE laboratories involved in membrane and electrode investigations. Now commercial MEAs and MEAs prepared by CEA are available for comparative in‑situ tests and laboratory scale CCM formulation is also available for ex-situ characterizations. The study of the degradation of the MEA at different stress factors is still running. Solvay Solexis performed the synthesis and extensive characterisation on the AQUIVIONTM membrane used within the project including proton conductivity, water uptake, mechanical stress and hydrogen crossover measurements. In addition, performance data of CCMs and chemical and physical characterisations of the necessary ionomer dispersion are available. The membrane was also preliminary characterised by CEA with SANS (small angle neutron scattering). The necessary detailed analysis to provide indications for further developments to Solvay-Solexis (related to deliverable D3.3) should be possible. Samples from operated single cell (electrodes, membrane and CCM) from different positions inside the cell were delivered from CEA to DLR for further ex-situ investigations.
A special focus of the DECODE project is on advanced modelling of porous media and the experimental characterization of gas diffusion layers. On major modelling activity, discussed in this paragraph, is the use of the relatively novel Lattice-Boltzmann technique for the description of porous media and complex fluid systems. In the Lattice-Boltzmann models the fluid consisting of fictive particles, and such particles perform consecutive propagation and collision processes over a discrete lattice mesh. Due to its particulate nature and local dynamics, LBM has several advantages over other conventional CFD methods, especially in dealing with complex boundaries, incorporating of microscopic interactions, and parallelization of the algorithm. An adaptation of lattice-Boltzmann tool waLBerla for an efficient parallelisation of the free-surface application was performed. Key assignment for this task is a local management of gas volume changes, and merge of independent gas regions. In addition also new algorithms for describing diffusion in porous media were developed. As a basis for the computational domains of the molecular dynamics of the MPL and the lattice Boltzmann model of the substrate, Opel provided a 3D synchrotron radiography data set of SGL GDM and handed it out to the partners who will convert it into computational domains for their respective models. To make the domain generation more convenient, Opel also provided a small set of image data carrying all relevant features of the original GDM image. Furthermore, Monte Carlo simulations of porous media are an important topic of DECODE based on structural models of the porous media. Three different type structures: fiber-, paper- and spaghetti- structures were generated and investigated. The distribution of PTFE was investigated on model surfaces and the models were verified through plausibility considerations of liquid water interactions. In addition, a pore network modelling tool (CEA) and a tool adapted from molecular dynamic modelling (UER) were developed and used for the simulation of transport processes.
GDL experimental characterization was performed by various methods like x-ray photoelectron spectroscopy, infra red spectroscopy, water porosimetry (in development) of artificially and naturally aged GDLs. Furthermore, neutron and synchrotron imaging and tomography results of fuel cells with relevance to GDL behaviour are generated in other projects, but can be used for DECODE. The methodological basis for investigation of porous media is exceptional in this project. It is expected that the experimental validation of the models will be achieved and that novel scientific results will be generated. This is especially important as the advanced characterisation of the diffusion media is lacking behind compared to the other fuel cell components. Artificial aged GDL materials were prepared by chemical and radiation treatment. The degradation of these artificial aged GDL was investigated by ex-situ methods. In addition natural aged GDLs from the short stack experiments in WP5 are available for single cell tests.
For the investigation of bipolar stacks DANA has provided 5 cell short stacks for Round Robin tests and for durability test. The first ageing results have been generated and are being analysed. It is also planned to use the GDL in the stack for investigating naturally aged GDL (link to WP4) with the methods described above. Within the project, an existing bipolar plate design "FRIEDA" from DANA Victor Reinz was selected for the test stack setup. The tested materials are uncoated SS316L, SS316L with 100nm electroplated gold coating, uncoated SS905L, and milled graphite composite. It is planned to iterate the different materials at different partners for testing under same conditions. The conditions of the durability run were defined within the DECODE Project with input from DLR, Opel and DANA. The first 1000 h durability test have been performed and the materials have been analysed. The tests are still in progress at the partners DLR, CEA, VOLVO, ZSW and DANA. 18 short stacks have be tested by the partners. The first results are reported in the deliverable D5.2.
Up to now ten stacks have been tested and fully analyzed. Twelve stacks finished the durability run and the post mortem analysis of the components is ongoing. One stacks to compare the test benches from each partner (round robin test) are still in operation. As well as the ongoing analysis of a single cell stack which was analysed under the lead of ZSW in the CONRAD (Cold Neutron Radiography) setup in Berlin.
The characterization and investigation of bipolar plates in durability measurements has started already. Presently, the components of the operated stacks are analysed with physical methods with various physical methods in order to identify the alteration induced by degradation processes. Contact resistances, water analysis and ex-situ surface analysis have been performed and the determination of trends and relationships are still ongoing.
Several publications and presentations concerning DECODE have already been realized. These are summarized below. DECODE was present in the “International Workshop on Accelerated Testing in Fuel Cells” with contributions of different partners (CEA, DLR, DANA, JRC etc. ). The coordinator was in the scientific committee of the work shop and the DECODE logo was on all announcements.
DECODE was presented at:
Further publications are
In October 2009 a workshop together with the EU-project AUTOBRANE were performed.
In general, the project has been successfully started and all work packages are active in the tasks planned. There are significant delays in some tasks, in particular in the preparation of the state-of-art-reports. Delays are also evident in the investigation of electrodes and membranes in CCMs. However, the overall goals are not endangered and it is expected that the delay can be completely recovered in 2009.
DECODE is organised within work packages, which are:
Work package 1: Project management and coordination
Work package 3: Investigation of Membrane and Electrodes degradation
Work package 4: GDL Degradation Characterization and Assessment
Work package 5: Investigation of Degradation of Bipolar Plates and Seals
Work package 6: Improved durability
Work package 7: Recommendation and Dissemination