From Catalyst Ink to PEM Fuel Cell Stack: First Full-Size Screen Printed Catalyst Layers Tested within a Generic Stack
Authors: Ney Linda , Herbst Dominic , Wengenmeyr Noah , Kiaee Zohreh , Thombra Neethu Philip , Häußler Frank , Joerissen Ludwig , Groos Ulf 
Published: December 2024

The PEM fuel cell industry is currently facing the challenge of upscaling its production, trying to reduce costs, allowing the fuel cell an easier entry in the mobility sector. Therefore, research on developing production processes, increasing throughput rates and quality control along the value chain is of special interest. Often, new materials, which show enhanced performance or durability are developed on very small scale. However, their key properties need to be investigated from a perspective of scalability, starting from catalyst ink to stack-level.

Fraunhofer ISE and Center for Solar Energy and Hydrogen Research (ZSW) had the unique opportunity to investigate the production parameters along the whole value chain of a PEM fuel cell: starting with the catalyst ink at Fraunhofer ISE and ending with a generic stack at ZSW [1]. This generic stack is the approach to have a standardized open access stack design for the industry and research community with the size (active area 283cm²) and power output corresponding to the current automotive market, developed by ZSW and EKPO [2].

In this study, the catalyst ink volume and catalyst layer area have been upscaled in a sheet-to-sheet process to meet the requirements of the generic stack automotive size membrane electrode assemblies (MEAs) with focus on heavy duty vehicles, hence aiming for platinum loadings of 0.4 mg/cm² (cathode) and 0.1 mg/cm² (anode). With on small scale proven ink recipes, specifically developed for screen printing cathode and anode electrodes [3], more than 50 catalyst layers have been produced with an upscaled area of 378cm² by a semi-automatic industrial screen printer. Flatbed screen-printing is a well-developed high throughput printing technology, known from printed electronics and solar cell metallization industries. Its benefit lies in the printability of high layer thicknesses with less solvent mass (high viscous pastes) and its degree of freedom to manufacture any structure, enabling platinum reduction in the electrodes by catalyst layer design.

The catalyst coated membranes (CCMs) have been manufactured by a decal transfer on state of the art membranes with a roll-calendar. Special focus lies on this challenging transfer process for larger active areas. Two different membrane types, two different decal foils and different transfer process parameters like velocity and temperature have been investigated for all. The optical and gravimetrical transfer yields are the most important quality parameters during transfer because they strongly affect the costs of CCM production, especially when platinum material is not transferred, sticking to the decal foil. The optimal transfer parameters have been chosen to further produce MEAs towards stack-level. Afterwards, the CCMs were cut to fit the generic stack format and sent to ZSW in Ulm, Germany.

At ZSW, the sub gaskets and gas diffusion layers (GDLs) from SIGRACET® SGL 22BB have been applied to form the 7-layer MEA. 15 CCMs have been stacked with bipolar plates and sealed to form a short stack. In addition, 15 commercially available CCMs were added as reference to the same stack. The whole manufacturing process chain is seen in Figure 1. After conditioning, the polarization curves have been measured at two different gas pressure settings. All other operating conditions were kept the same.

As can be seen in Figure 2, the screen printed CCMs from Fraunhofer ISE (red) show very similar performance in comparison to the commercial reference (black) within the stack. In addition, the voltage deviation between the CCMs is slightly smaller for the ISE-CCMs, indicating a very good reproducibility in production. This study showed for the first time that screen printed catalyst layers can be upscaled to industrial active areas, overcoming challenges in printing, drying and transfer, while reaching similar performance as commercial references in a short stack. In future experiments many more iterations along the production chain will follow, to further improve the stack performance and investigate the effect of production pathways, process parameters and new materials.

[1] “HyFab-BW - HyFab-Baden-Württemberg”, https://www.ise.fraunhofer.de/en/research-projects/hyfab-bw.html; Fraunhofer ISE, accessed April 2024

[2] “Manufacturer-independent fuel cell stack: an innovative development platform for industry and science”, https://www.zsw-bw.de/en/research/fuel-cells/topics/stack-technology.html; ZSW; accessed April 2024

[3] L. Ney, J. Hog, R. Singh, N. Göttlicher, P. Schneider, S. Tepner, M. Klingele, R. Keding, F. Clement, U. Groos, J Coat Technol Res 20 (2023) 73–86. https://doi.org/10.1007/s11998-022-00710-1.

Figure 1