CNTs Grown on Al2O3 Spheres As an Efficient Catalyst Support for High Performance MEA in PEM Fuel Cells

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) have been widely accepted as a clean energy device because of its capability of generating high energy density and only water as a product via direct converting of the chemical energy into the electrical energy. However, durability problems originating from the carbon corrosion and Pt agglomeration have been one of the major issues for practical applications. The high potentials formed in a cell during the fuel cell operations lead to serious carbon corrosion in catalyst layers, which causes the decrease of cell performance. To resolve the carbon corrosion, highly durable carbon materials such as carbon nanotubes (CNTs) have been intensively studied. Although the corrosion-resistant characteristics of CNTs were efficient to utilize as an electrocatalyst support for PEMFCs, the difficulty in processing the CNTs mainly due to poor dispersibility and easy bundle formation in a catalyst ink limited their practical applications. In this respect, vertically aligned carbon nanotubes (VACNTs) have been tried and showed promising results in a PEMFC MEA. However, VACNTs need complex process to make MEAs, remaining the issues of mass production. In this work, we report CNTs grown on Al2O3 (Al2O3-CNT) as an efficient support material for PEMFC MEAs. The catalyst support was designed to utilize durable CNT properties while resolving the CNT bundling problems. The catalyst was characterized by transmission electron microscope (TEM), field emission scanning spectroscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) in order to investigate structural and electronic properties. The kinetics of O2 reduction is examined with the rotating disk electrode (RDE) technique. A potential cycling test was applied to evaluate durability of the catalyst. The electrochemical surface area (ECSA) of Pt/Al2O3-CNT slightly decreased (17 %), while Pt/C loses nearly 46 % of its ECSA of its initial value over repeated cycling test under carbon corrosion potential range, representing more durable properties of CNTs. The single cell test was also performed with Pt/Al2O3-CNT and Pt/C after fabricating the catalysts to MEAs. The performance of the Pt/Al2O3-CNT was comparable to that of Pt/C and showed better performance at high current density regions. Furthermore, after the accelerated stress test (AST), the Pt/Al2O3-CNT also showed approximately 2 times higher stability than Pt/C in a single cell test.