Development of the overpotential simulator for polymer electrolyte fuel cells and application for optimization of cathode structure Tatsuya Hattori a , Ai Suzuki b , Riadh Sahnoun a , Michihisa Koyama a , Hideyuki Tsuboi a , Nozomu Hatakeyama a , Akira Endou a , Hiromitsu Takaba a , Momoji Kubo a , Carlos A. Del Carpio a , Akira Miyamoto a,b, * a Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan b New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan 1. Introduction Polymer electrolyte fuel cell (PEFC) is a promising power source especially for mobile applications due to the zero- or low-emission quality, the high efficiency and the high power density. To commercialize the PEFC, the improvement of the performance and the cost reduction are required. The cathode catalyst layer is known as a component that largely influences PEFC performance and cost because of the large overpotential, which requires larger Pt loadings. Though constructing the efficient electrode micro- structure is important to overcome this problem, it is difficult to design the best cathode microstructure because the cathodic reaction involves a variety of phenomena. Therefore, many researchers have tried to optimize the cathode microstructure experimentally [1–3] and theoretically [4,5]. Searching the optimal ionomer content [1], the Pt loading [2] and distribution of ionomer in the catalyst layer [3] experimentally need a number of trials and errors. While some theoretical approaches [4,5] have proposed the optimal ionomer content, the Pt loading and the catalyst layer thickness. However, simple expression of complex cathode microstructure by simple parameters such as a porosity, a tortuosity factor, a thickness and mass percentages of components cannot address the influence of the cathode microstructure such as configuration of support material, proton and electron current paths in the ionomer and the carbon network, etc. To consider the influence of the cathode microstructure, constructing the model that consider the configuration of support material and ionomer is effective. Until now, three-dimensional model that consider the configuration of cathode has not been reported though two- dimensional model has already been proposed [6]. We have already developed a novel simulator that can deal with complex irregular porous structure and applied it to the investigation of overpotential characteristics of solid oxide fuel cell [7]. In this work, the new simulators were developed to model the three-dimensional cathode catalyst layer of PEFC and to simulate the overpotential characteristics for the constructed Applied Surface Science 254 (2008) 7929–7932 ARTICLE INFO Article history: Available online 4 April 2008 PACS: 82.45.Fk 82.47.Nj 78.55.Mb 82.20.Wt Keywords: Polymer electrolyte fuel cell Cathode Microstructure Overpotential Optimization ABSTRACT We developed a novel computational method to investigate the influences of the microstructure of the polymer electrolyte fuel cell cathode catalyst layer on the overpotential characteristic toward its optimization. Three-dimensional cathode catalyst layer models were constructed by applying three- dimensional porous structure simulator and developed simulator was used to study the overpotential characteristics. Our results showed that the overpotential decreased as decrease of the standard deviation of the ionomer thickness distribution due to the increase of number of active sites. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author at: New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan. Tel.: +81 22 795 7233; fax: +81 22 795 7235. E-mail address: miyamoto@aki.che.tohoku.ac.jp (A. Miyamoto). Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.03.165