MPL/GDL-Supported Pt Electrocatalysts for PEFCs

Abstract

Introduction Currently, Pt electrocatalysts supported on carbon black (Pt/C) are widely used in polymer electrolyte fuel cells (PEFCs). However, carbon corrosion can occur on the cathode side especially during start-stop cycles, leading to performance degradation of PEFCs (1). To solve this technological issue, we have developed SnO2 and TiO2 support materials dispersed on graphitized carbon materials acting as the conductive backbone, exhibiting high durability (2-4). Here in this study, we focus on non-carbon support such as Nb-doped TiO2 which is stable under both anode and cathode conditions. In addition, we prepared various electrocatalyst layers directly on the microporous layer (MPL) coated on the gas diffusion layer (GDL) to simplify membrane electrode assembly (MEA) structure and manufacturing processes. Non-carbon support was deposited on the MPL/GDL by using arc plasma deposition (APD), and Pt catalyst nanoparticles are then deposited on this porous substrate to prepare a “Pt/non-carbon support/MPL/GDL” structure, as schematically shown in Fig. 1. MEAs can be prepared just by heater-pressing this integrated structure with the polymer electrolyte membrane. Experimental By using APD, various non-carbon support materials were deposited on the MPL/GDL structure, and then Pt catalysts were deposited on it to prepare “Pt/non-carbon support/MPL/GDL” structures. Their microstructure was observed by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and transmission electron microscopy (TEM). Electrochemical measurements were performed with single cells. Their performance was measured and compared by varying preparation conditions such as voltage of APD or types of GDL used. Results and discussion Figure 2 shows a STEM image of the Pt/Ti(Nb)O2/MPL/GDL structure after 100 APD pulses for Ti(Nb)O2 support and 500 pulses for Pt catalyst by APD. Pt particles of a few nm in average diameter on the MPL/GDL were observed. Figure 3 shows I-V characteristics of MEAs with the Pt/Ti(Nb)O2/MPL/GDL structure, in which Pt was deposited on the MPL/GDL by 70, 100, and 150V of APD. I-V characteristics of an MEA with the standard Pt/C catalyst (Tanaka Kikinzoku, TEC10E20E) are also shown for comparison, with the common cathode Pt loading of 0.024 mgPt/cm2. For this considerably low Pt loading, higher cell performance was obtained in case Pt was deposited by 100V of APD. Further improvement in electrochemical performance is however needed to realize such catalyst-integrated MPL/GDL structures. Acknowledgment Financial support by the Center-of-Innovation program, JST Japan, is gratefully acknowledged.