Screening Binary and Ternary Catalyst Formulations for Direct-Methanol-PEM Fuel Cells

Abstract

In an exploratory approach binary and ternary nanodisperse alloy catalysts were synthesized containing the elements Pt, Ru and W, Mo or Sn, respectively. The catalysts were prepared applying a colloid method developed by Bonnemann, which was found to be highly suitable for synthesizing this kind of supported catalyst, as determined by TEM, EDX and electrochemical measurements. The catalysts were tested for their activity towards anodic oxidation of H 2 /CO-mixtures and methanol in PEM single cells. It turned out that for H 2 /CO oxidation, the systems Pt/Ru/W and - at higher overpotentials -Pt/Ru/Sn were the most active systems, for methanol oxidation again Pt/Ru/W was the most active system. By varying the molar composition of the system Pt/Ru/W it was found that both for oxidation of H 2 /CO and methanol the most active system tested was a ternary catalyst with a molar ratio Pt/Ru/W of 1/1/1,5. In another series of experiments the cocatalytic activity of some transition metal phtalocyanine complexes was investigated. It turned out that none of the systems tested had a beneficial effect on oxidation of H 2 /CO, for methanol oxidation the systems Pt/Cobaltphtalocyanine and Pt/Nickelphtalocyaninetetrasulfonic acid showed a cocatalytic activtiy. For Pt/Nickelphtalocyaninetetrasulfonic acid, the effect can still be enhanced by pyrolyzing the complex. Furthermore, a pre-screening method for methanol oxidation is introduced which makes it possible to test a number of electrocatalyst systems at the same time using graphite model electrodes which are covered with a thin layer of catalyst and ionomer.