Investigation of Multilayered Catalyst Layers for Polymer Electrolyte Fuel Cells by Electrospray Deposition

Abstract

Due to problems such as environmental pollution and global warming, fuel cells are attracting attention as an energy source with low environmental load. As a type of fuel cells, there is a growing demand for polymer electrolyte fuel cells that can operate at low temperatures and are suitable for miniaturization. Improved power generation performance is required to increase the penetration of this technology. The performance of a fuel cell depends on the structure of the catalyst layer (CL), which is directly involved in the reaction. The structure of the CL mainly depends on the composition and the coating method. Recently, a method has been proposed in which ion and gas transportation is made more efficient and the performance is improved by changing the ionomer distribution in the thickness direction. However, in order to change the ionomer distribution, precise control of the coating amount is required, and there are few actual formation examples and the coating method is limited. Therefore, coating methods that have not yet been investigated should also be considered. In this study, the electrospray deposition (ESD) method was used to prepare the CLs, and the comparison of the power generation performance and the effect on the CL structure were investigated. In order to change the ionomer distribution in the thickness direction, multi-layered CLs with different ionomer to carbon ratio (I/C ratio) were formed, and the power generation performance was compared with that of the homogeneous CLs. Several homogeneous CLs with different I/C ratios were formed and the CLs were observed with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The maximum output power density was 274 mW cm-2 and 312 mW cm-2 for the homogeneous and three-layer CLs, respectively. Therefore, it was found that the structure in which the distribution of ionomers is changed in the thickness direction is effective in improving the performance of the CL formed by ESD. The SEM-EDS observation revealed that the agglomeration of particles became more pronounced and the CL became thinner as the I/C ratio increased. The result suggest that it is necessary to take into account the change in thickness with the amount of ionomer in order to form an ideal CL structure using ESD.