Polymer electrolyte membrane (PEM) water electrolysis is an attractive way of producing carbon-free hydrogen. One of the drawbacks of this method is the need for precious metalbased electrocatalysts. This calls for a highly efficient utilization of the precious metal, which can be obtained by dispersing the precious metal compound onto a catalyst support. Electrocatalysts with 50, 70 and 90 wt.% of IrO2 on a TaC support were tested in a laboratory PEM water electrolyser and compared with pure IrO2. The temperature was set at 90, 110, 120 and 130 degrees C respectively and the cell voltage was varied between 1.4 and 1.8 V. The load characteristics and electrochemical impedance spectra were obtained and compared for a range of electrocatalysts. The highest current densities and the lowest charge transfer and cell resistances were found for the 70 wt.% IrO2 electrocatalyst. By contrast, the pure IrO2 electrocatalyst showed the lowest current densities and the highest charge transfer and cell resistance. For example, the relative difference in current densities between the 70 wt.% IrO2 and the pure IrO2 electrocatalyst attained 36% at 130 degrees C and 1.7 V. All of the supported electrocatalysts showed a higher efficiency of utilization of the precious metal than the pure IrO2. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.