One of the main aims of the research on fuel cells is creating the most efficient electrocatalysts for oxygen reduction. The platinum based catalysts have been so far most commonly used systems for cathodes. However the problem is the high activity of Pt towards methanol oxidation, which reduces possibility of its using as cathode in Direct Methanol Fuel Cells (DMFCs) in which methanol crossover through the polymer membrane from the anode to the cathode can occur. Direct reaction of a fuel with catalyst at the cathode leads to its depolarization and to the drop of the cell power. An interesting alternative to Pt-based catalysts in DMFCs can be RuSex nanoparticles, because of it’s high methanol tolerance. But to make system more attractive, the potential of the oxygen reduction should be shifted towards more positive values. This feature has been recently achieved by us via modification of carbon-supported RuSex nanoparticles with ultra-thin films of tungsten oxide (WO3).
In this work we utilize the iridium nanoparticles (obtained by sol-gel method) as the addition to RuSex/C catalyst. Ir surface can be partially oxidized during potential cycling and as a result the mixture of Ir with mixed valent oxides (IrOx) is formed. Ir oxides are characterized by good electronic conductivity, the property necessary to enhance O2 reduction. Apart from that, just like in the case of WO3, iridium structures are highly active towards hydrogen peroxide reduction, thus supporting direct reduction of oxygen to water. The TEM images illustrate that nanostructural Ir makes compact polymeric type structure analogous to those previously observed for WO3. It is reasonable to expect that IrOx may serve as a matrix for carbon-supported RuSex particles. Analysis of voltammetric and RDE experiments shows that, after modification of RuSex by iridium nanoparticles, better catalytic properties of the cathode, namely the positive shift of the reaction potential and the increase of the reaction rate (in comparison to bare RuSex and Ir/IrOx systems) have been obtained.