PEFCs Using Metallic Ti and Sn Gas Diffusion Layers

Abstract

Introduction Many types of carbon materials are used in PEFCs. Especially, gas diffusion layer (GDL), with a thickness of ca. 0.2 mm are made of relatively expensive carbon fibers. In general, metallic materials can be more electronically conductive than carbon black based materials, and thinner GDLs could be prepared using metals. Here in this study, we evaluate and compare several types of metallic materials to apply as GDLs. Using such alternative metallic GDLs, current-voltage (I-V) characteristics were measured and overvoltages were separated. The purpose of this study is to examine possibilities of metallic GDLs for PEFCs, by varying materials, thickness, porosity, and preparation conditions. Experimental We measured I-V characteristics of PEFCs using metallic GDLs. Four types of porous metallic sheets were used as GDLs, shown in Figures 1 to 3: (i) Ti fiber-based sheet (porosity: 70%; thickness: 200μm; Nikko Techno Ltd.), (ii) Ti fiber-based sheet with porous Sn layer, (iii) Ti punching metal sheet (sheet thickness: 12μm; hole diameter: 300μm; Fukuda Metal Foil & Powder Co., Ltd.), and (iv) Sn punching metal sheet (sheet thickness: 100μm; hole diameter: 300μm, Fukuda Metal Foil & Powder Co., Ltd.). Except for cathode-side GDLs, standard materials were used such as Pt/C electrocatalyst (Tanaka Kikinzoku Kogyo, TEC10E50E). Electrochemical impedance spectroscopy (EIS, Solartron 1255WB) was used to separate overvoltages in the electrochemical characterization. Results and discussion I-V characteristics of the cells with the cathode GDLs (i) to (iv) are shown in Figure 4. Decrease in cell performance was mainly caused by an increase in ohmic losses. Comparing these GDLs, Sn-based materials are generally more conductive than Ti-based materials to decrease ohmic losses, but concentration overvoltage can also be high when the GDLs (ii) and (iv) were used. Both contact and internal resistance were reduced when using the porous Ti punching metal sheet instead of the Ti fiber sheet. Further study is in progress to increase I-V characteristics of MEAs by optimizing materials selection and structure. Acknowledgement Financial support from New Energy and Industrial Technology Development Organization (NEDO) is gratefully acknowledged (Contract No. 20001214-0). References Larminie，A. Dicks，Fuel Cell Systems Explained, 2nd Edition, John Wiley & Sons, West Sussex, England, 2003.T．Kitahara，T．Konomi，H．Nakajima, and J．Shiraishi， Japan Soc. Mech. Engineers, B76 (761) 101 (2010), in Japanese.S．Matsumoto，M．Nagamine，Z．Noda，J．Matsuda，S．M．Lyth，A．Hayashi，and K．Sasaki，J ． Electrochem ．，165 (14)，1165 (2018).C．A．Reiser，L．Bregoli，T．W．Patterson，J．S．Yi，J．D．yang，M．L．Perry，and T．D．Jarvi，Electrochem . Solid-State Lett.，8 (6)，A273 (2005). Figure 1