MEA Manufacturing Technology
Scale-up
Methods for manufacturing functional coating systems (membrane electrode assemblies (MEAs)) are usually first developed on a laboratory scale. New ideas and methods can thus be tested using small amounts of material on the gram or milliliter scale. Whenever a method seems promising, material volumes of up to several kilograms are needed for larger-scale experiments (pilot plant tests). Often it turns out that the laboratory methods cannot be used for these tests because the materials exhibit different behaviors. For example, a laboratory-manufactured catalyst–solvent dispersion can be processed into a layer of several square centimeters within minutes. Manufacturing a layer of several square meters, in contrast, can take well over an hour. Thus, the time scale for manufacturing dispersions in a laboratory is different to a technical facility. A dispersion that is only stable for 10 minutes may be suitable for laboratory applications, but not for larger-scale approaches. The issue of scale-up – i.e. adapting MEA production methods to larger (temporal and spatial) scales – is thus relevant for several activities at IEK-14, including the production of polymer electrolyte electrolyzers and fuel cells.
Correlation between process parameters and MEA properties
Scale-up requires knowledge of the correlation between the material, process, and performance parameters of the MEA produced. To identify scale-up rules, it must be known which of these parameters influence the MEA performance. For this purpose, extensive process analytics are being developed at IEK-14 that focus on the following process steps:
The structure formed during this manufacturing process is decisive for the electrochemical performance of the MEA because it has a large influence on the physico-chemical processes in the electrode.
Structure formation processes
The structure in the electrodes results from factors such as the rheological structure in the dispersion used for manufacturing and its behavior during the coating and drying processes.
Rheology of the dispersion
Depending on the rheological structure in the dispersion and the free surface energy of the substrate, the coating process leads to different changes in the dispersion. Using rheological and tensiometric investigations, these influences on the dispersion can be clarified.
Drying the dispersion
During the drying process, the solvents vaporize at different drying rates, which causes the solids in the dispersion to agglomerate to porous structures. This layer formation process is closely interconnected to the time-dependent progression of the chemical composition of the wet layer all the way to the dry electrode. By adapting thermodynamic parameters, this progression can be controlled so that crack formation can be influenced, for example. To analyze these processes, a spectroscopy-based measurement technique was developed at IEK-14, which simultaneously enables the reproducibility of the electrode fabrication to be examined.
Analyses of the correlation between dispersion composition, rheology, and tensiometry of the dispersion, as well as the dispersion drying behavior are priorities that are thoroughly investigated at IEK-14. Understanding structure formation processes is the key to identifying scale-up rules. This permits the transfer of the results from laboratory development to large-scale production. Furthermore, these insights are used to develop new fabrication methods to make the production of MEAs simpler, faster, and therefore cheaper. For example, an MEA fabrication method was developed at IEK-14 that requires fewer process steps than conventional production methods while at the same time producing less waste. This “completely coated MEA” (CC-MEA) method involves producing the two electrode layers and the membrane solely via slot-die processes, which dispenses with the need for a separate membrane and the assembly step.
Literatur:
A. Stähler, M. Stähler, F. Scheepers, M. Carmo, D. Stolten
Reusability of decal substrates for the fabrication of catalyst coated membranes
Int. J. Adhesion and Adhesives (2019)
https://doi.org/10.1016/j.ijadhadh.2019.102473
F. Scheepers, A. Stähler, M. Stähler, M. Carmo, W. Lehnert, D. Stolten
Steering and In-situ Monitoring of Drying Phenomena during Film Fabrication
J. Coat. Technol. Res. 16 (2019) 1213-1221
https://doi.org/10.1007/s11998-019-00206-5
M. Stähler, A. Stähler, F. Scheepers, M. Carmo, D. Stolten
A completely slot die coated membrane electrode assembly
Int. J. Hydrogen Energy 44 (2019 ) 7053-7058
https://doi.org/10.1016/j.ijhydene.2019.02.016
F. Scheepers, A. Stähler, M. Stähler, M. Carmo, W. Lehnert, D. Stolten
Layer Formation from Polymer Carbon-Black Dispersions
Coatings 8 (2018) 450
https://doi.org/10.3390/coatings8120450
A. Burdzik, M. Stähler, M. Carmo, D. Stolten
Impact of reference values used for surface free energy determination: An uncertainty analysis
Int. J. Adhesion and Adhesives 82 (2018) 1–7
https://doi.org/10.1016/j.ijadhadh.2017.12.002
F. Scheepers, A. Stähler, M. Stähler, M. Carmo, W. Lehnert, D. Stolten
A new setup for the quantitative analysis of drying by the use of gas phase FTIR-spectroscopy
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https://doi.org/10.1063/1.5036817
A. Burdzik , M. Stähler, I. Friedrich, M. Carmo, D. Stolten
Homogeneity analysis of square meter-sized electrodes for PEM electrolysis and PEM fuel cells
J. Coat. Technol. Res. 15 (2018) 1423-1432
https://doi.org/10.1007/s11998-018-0074-3
M. Stähler, I. Friedrich
Statistical investigations of basis weight and thickness distribution of continuously produced fuel cell electrodes
J. Power Sources 242 (2013) 425-437
https://doi.org/10.1016/j.jpowsour.2013.05.073