Preparation of Three-Dimensionally Networked Composite of Carbon Electrode for PEMFC

Abstract

This paper proposes novel types of electrodes available for proton exchange membrane fuel cells (PEMCs), in which three-dimensional channels of carbon fibers (CFs), carbon-nanotubes (CNTs) and a polymer-electrolyte (PE) are connected with one another. A particular feature of fabricating a type of electrode is physical coating of CFs with CNTs. A suspension of CVD-synthesized CNTs was sprayed onto/into a gas-diffusion electrode (carbon paper consisting of three-dimensional network of CFs) heated at a temperature well above the boiling point of the matrix solvent. Not only CFs at the top surface of but also those inside the carbon paper were coated uniformly with dense and extremely thin (< 1 µm) layers of CNTs. Then, PE channels were formed within the CNT layers by means of a dip coating technique. CFs could also be chemically coated with CNTs by a novel CVD method applying forced flow of H₂ gas containing carbon and catalyst sources through the carbon paper. CNTs with lengths up to several micron meters were formed with a population density of 10⁹ cm^-2 or even higher. Employing CNTs not particulate but fibrous in shape is expected to maximize the efficiency of contact among Pt catalyst, PE and the gas phase inside the electrode, eliminating negative factors limiting performance of current PEFCs such as low utilization efficiency of Pt catalysts and suppressed diffusion of reactant/product gases through the catalyst layer.