Preparation and characterisation of Pt-Ru model electrodes for the direct methanol fuel cell

Pt-Ru alloys for the direct methanol fuel cell (DMFC) with Ru contents between 10 and 60 at.% were synthesised in two ways: on the one hand, polycrystalline Pt-Ru reference samples were prepared by arc melting starting from appropriate mixtures of Pt and Ru powders. On the other hand, nanocrystalline Pt-Ru particles of about 8 nm were electrochemically deposited in carbon/Nafion [reg] layers on glassy carbon discs for electrochemical measurements. The structural properties of the Pt-Ru model electrodes, such as lattice constant, grain size and alloy composition, were investigated by X-ray line shape analysis and scanning electron microscopy (EDX). Analysing the continuous peak shift of the Pt Bragg reflexes with increasing Ru content, we established a calibration curve for Pt-Ru alloys which allows to determine the Ru content of samples with unknown composition by simple XRD measurements. The Pt-Ru samples were electrochemically characterised recording quasi-stationary current-potential curves with regard to the influence of the Pt-Ru composition on the methanol oxidation. The Pt-Ru catalyst with 50 at.% Ru turned out to be most active for the methanol electrooxidation