Pt-Decorated Oxide/MPL/GDL-Supported PEFCs

Abstract

Introduction Pt electrocatalysts supported on carbon black (Pt/C) are typically used in polymer electrolyte fuel cells (PEFCs). Carbon black has high electronic conductivity and large specific surface area for dispersing Pt catalysts. However, carbon corrosion occurs on the cathode side especially after start-stop cycles, leading to performance degradation of PEFCs[1-3]. To solve this technical issue, in this study, we directly prepare non-carbon support such as Ti-Nb alloy, which is stable under cathode conditions, on the microporous layer (MPL) coated on the gas diffusion layer (GDL). Using arc plasma deposition (APD) technique, Pt catalyst nanoparticles are then deposited on the non-carbon support to prepare a “Pt/non-carbon support/MPL/GDL” structure (Figure 1). Membrane electrode assembly (MEA) can be prepared just by heater-pressing this catalyst-integrated porous structure. This PEFC concept for better mass productivity is proposed and its electrochemical performance is examined. Experimental Non-carbon support was deposited on the MPL/GDL by 100 pulses of APD, and then Pt catalysts were deposited on it by 500 pulses of APD, with the Pt loading of ca. 0.024mgPt/cm2 to prepare the “Pt/non-carbon support/MPL/GDL” structure. The microstructure of the electrode structure was observed by SEM, STEM, and TEM. Chemical composition was analyzed by EDS and ICP. Electrochemical measurements were performed with single cells and their performance was compared by changing preparation conditions such as Pt loading. Results and discussion Figure 2 shows the STEM image of the MPL/GDL after 500 pulses of the APD for Ti support and Pt catalyst, showing Pt particles of a few nm in average diameter on the MPL/GDL. EDS analysis revealed that Ti and Pt mainly locate within the range of 0.1 to 0.2 μm from the MPL top surface. Figure 3 shows current-voltage (I-V) characteristics of MEAs using Nb-doped TiO2, Ti-Nb alloy, and W as non-carbon supports deposited by APD. The I-V results are also shown for an MEA fabricated by directly depositing Pt on MPL/GDL without non-carbon support and an MEA prepared by spray printing the standard Pt/C catalyst with the same Pt loading (0.024mgPt/cm2). The highest cell performance was obtained when Nb-doped TiO2 was used as the non-carbon support, whilst it was still less than that with the standard Pt/C catalyst. In order to further improve cell performance, the APD pulse of Pt deposition was increased from 500 times to 1000 times, and 2000 times. However, droplet was formed and the cell performance was declined, so that the APD conditions have to be varied to further improve cell performance. In the future, start-stop and load cycle durability should also be analyzed to exceed the performance using the standard Pt/C catalysts.