Methanol-tolerant oxygen reduction catalysts based on transition metal sulfides and their application to the study of methanol permeation

The oxygen reduction activity and methanol tolerance of a range of transition metal sulfide electrocatalysts have been evaluated in a liquid-feed solid-polymer-electrolyte direct methanol fuel cell. These catalysts were prepared in high surface area form by direct synthesis onto various surface functionalized carbon blacks. Of the materials tested, catalysts based on (MRu5S5)-Ru-a/Ketjen black (M-a = Rh or Re) were found to be the most active, and a cell utilizing a RhRu5.9S4.7/Ketjen black cathode gave working cell voltages at 100 mA cm(-2) within 100 and 80 mV of that obtained using a Pt cathode for 2 and 4 M methanol anode feed concentrations, respectively, where methanol permeation gave rise to appreciable degradation in Pt performance. Performance could be further enhanced in the cell by increases in methanol feed concentration and pressure. Finally, the low level of activity of our cathode catalysts to methanol electro-oxidation allows us, for the first time, to measure methanol permeation in Nafion-based fuel cells under realistic operational conditions. We have modelled this how, and used our data both to verify the model and to establish sensible parameters. (C) 2000 Elsevier Science Ltd. All rights reserved.