Electrocatalysts for Direct Alcohol Oxidation Fuel Cells Prepared Using Ion Beam Assisted Deposition Technique

Abstract

Active layers of the electrocatalysts for oxidation of methanol and ethanol were prepared by ion beam assisted deposition (IBAD) of platinum and activating rare earths metals (Ce, Yb) onto carbon (AVCarb® Carbon Fiber Paper Р50 and Toray Carbon Fiber Paper TGP-H-060 Т) supports. The deposition method is characterized by the use of deposited-metal ions as assisting ions. Metal deposition and mixing between the precipitable layer and surface of the substrate by accelerated ions of the same metal were carried out on the experimental unit from a neutral vapor fraction and the vacuum-arc discharge plasma of a pulsed electric arc ion source, respectively. Ion accelerating voltage is 10 kV; vacuum – 10– 2 Pa. Investigation of the composition and microstructure of layers was carried out by RBS, SEM, EPMA and XRF methods. It has been established that the obtained catalytic layers contain atoms of the deposited metals and substrate material, as well as impurity oxygen atoms; their thickness reaches ~30–100 nm. Content of platinum atoms in the layers is ~2×1016 cm–2, concentration of deposited metals atoms in the maximum of distribution equals about a few at.%. According to investigations with use of cyclic voltammetry the electrocatalysts with prepared layers exhibited high catalytic activity in the reactions of electrochemical oxidation of methanol and ethanol, which form the basis for the principle of operation of low temperature fuel cells (DMFC and DEFC) (Figure 1). Figure 1. Cyclic voltammograms in the ethanol comprising solution of electrocatalyst prepared using ion beam deposition of ytterbium and platinum onto Toray Carbon Fiber Paper TGP-H-060 Т In comparison with the traditional multistage chemical methods of preparation of the deposited catalysts, the proposed IBAD method appears to be promising and often more preferable. It allows of the introduction of micro amounts of a doping impurity in the near-surface of a substrate under non equilibrium conditions and of the formation of cohesive catalytic layers at ultra-low platinum consumption. Figure 1