Effect of thermal treatment of IrO2 anode catalysts for PEM water electrolysis

IrO2 powders for use as anode catalysts for PEM water electrolysis cells, were prepared and then annealed at different temperatures and compared as oxygen evolving catalysts in a PEM cell. Best performance of the catalysts, at high current densities, was obtained when annealing at 490degreesC for 8 hours. Here the best compromise between electrocatalytic activity i.e. the number of active points at the surface and the electrical conductivity, seems to be achieved. The electrical conductivity of the oxide catalyst is found to increase by increasing annealing temperature whereas the activity of the catalyst decreases at higher annealing temperatures. The importance of high electrical conductivity of the catalyst is emphasized and may be related to the geometry of the porous backing/current collector. The catalysts were studied in situ in a PEM cell by voltammetry, AC-impedance and stationary current density-potential measurements. Particle size and crystallinity were studied by transmission electron microscopy (TEM).