Bifunctional electrocatalytic IrO2-SnO2 nanopowders : the kinetic of the oxygen Reduction Reaction by Rotating Disk Electrode

Proton Exchange Membrane Fuel Cell (PEMFCs) are currently developed as devices for distributed power supply. In these systems the Oxygen Reduction Reaction (ORR) at the cathode causes large overpotentials at the lower operating temperatures. Currently, Pt-based electrocatalysts are the most widely used at low temperature1, then the development of platinum free catalysts able to reduce the significant voltage losses at the cathode is therefore highly demanded. Among the different materials that can replace platinum in an acidic environment, IrO2-based catalysts are very promising2, particularly in view of the development of bi-functional fuel cell/water electrolysis systems. IrO2, pure and in admixture with other cheaper oxides, is well known for both its stability in acidic media and its electrocatalytic activity for Oxygen Evolution Reaction3 (OER). On this ground, ORR activity of IrO2-based nanostructured powders with different Ir contents, synthesized by sol-gel technique, was evaluated using Glassy Carbon Rotating-Disk Electrode (GC-RDE) as the support, and a thin Nafion® film as gluing agent. RDE allows one to study the activity of a material under fast and well-defined mass transfer conditions, so charge transfer limitations can be singled out. The catalytic behaviour of the ORR was evaluated both by voltammetric techniques in HClO4 0.1M at 25°C. The results demonstrate the high activity of these materials, even at low IrO2 contents. Interesting features about the dependence of the ORR kinetics on the IrO2 loading are highlighted.