Fabrication of Cathode Catalyst Layer by Use of Multi-Nozzle Electrospray Method on Polymer Electrolyte Fuel Cells

We have been researching manufacturing methods of catalyst layers to improve the effective utilization rate of Pt in polymer electrolyte fuel cells. In our previous research 1-3, we demonstrated experimentally that an electrospray (ES) method was able to make great progress in the interface formation between the electrolyte polymer ionomer and the Pt supported on carbon 1,3 or conductive ceramics 2 , and that the immediate drying of the catalyst layer ink also greatly contributes to the improvement of Pt effectiveness. Since the ink droplets had already dried when these were deposited on the membrane, we proposed that the ink drying process can be reduced and that the cost of producing the catalyst layer is also greatly reduced. However, since the amount of catalyst applied is very small with a single nozzle, we also proposed that a multi-nozzle system is indispensable in order to adapt to the actual catalyst layer formation process. Therefore, we are jointly developing the ES manufacturing system with a multi-nozzle device (Fig. 1a) in a collaboration between the University of Yamanashi and Meiko Co., Ltd. We developed the first prototype machine, MES-Lab.α, for R & D, which features options such as nozzle material, multi-nozzle structure, coating treatment of nozzle tip, nozzle fixing adhesive, suck-back method, and ink energization method, among others. We have completed a new design for a basic 72-nozzle block (Fig. 1b), which incorporates all the above new materials and new structures and is compatible with the production of industry-standard electrodes (5 cm x 5 cm). We have developed a new system to control and maintain the shape of the Taylor cone, which is essential for stable coating. This is a device that precisely controls the internal pressure of the ink tank above the nozzle (Fig. 1b). We are also developing a multi-nozzle to increase the coating rate. With conventional methods, the quantity of spray depends on the nozzle diameter, but with the ES method it does not. To increase the ejected quantity for ES, the number of nozzles must be increased. We developed a 72-pin multi-nozzle, for which the coating rate is enough for research devices but not for mass production. It is estimated that more than 1000 pins are required for a mass-production multi-nozzle device. However, it is very inefficient to develop a nozzle device with 1000 pins by trial and error. It was found that the results of an electric field simulation show similarity to the actual distribution of the catalyst layer after coating (Fig. 2). We have introduced this simulation technique for the optimization of the multi-nozzle design. We believe that the design of the nozzle model using simulation will greatly contribute to the development of efficient, low-cost mass production equipment. Acknowledgement This work was partially supported by funds for the SPer-FC, the ECCEED’30-FC, and the ECCEED_ES projects from NEDO and the FCyFINE project from the Regional Innovation Ecosystems Program of MEXT. References K. Takahashi, K. Kakinuma, and M. Uchida, J. Electrochem. Soc., 163 , F1182-F1188 (2016). K. Takahashi, R. Koda, K. Kakinuma, and M. Uchida, J. Electrochem. Soc., 164 , F235-F242 (2017). S. Cho, K. Tamoto, and M. Uchida, Energy Fuels, 34 , 14853−14863 (2020). Figure 1