A novel Ir0.5Mn0.5O2 cathode has been synthesized by thermal decomposition of mixed H2IrCl6 and Mn(NO3)(2) water solution. The Ir0.5Mn0.5O2 cathode has been characterized by XRD, field emission SEM (FESEM) and AC impedance spectroscopy. XRD result shows that rutile-structured Ir0.5Mn0.5O2 phase is formed by thermal decomposition of mixed H2IrCl6 and Mn(NO3)(2) water solution. FESEM micrographs show that a porous structure with well-necked particles forms in the cathode after sintering at 1000 degrees C. The average grain size is between 20 and 30 nm. Two depressed arcs appear in the medium-frequency and low-frequency region, indicating that there are at least two different processes in the cathode reaction: charge transfer and molecular oxygen dissociation followed by surface diffusion. The minimum area specific resistance (ASR) is 0.67 Omega cm(2) at 800 degrees C. The activation energy for the total oxygen reduction reaction is 93.7 kJ mol(-1). The maximum power densities of the Ir0.5Mn0.5O2/LSGM/Pt cell are 43.2 and 80.7 mWcm(-2) at 600 and 700 degrees C, respectively. (c) 2008 Elsevier B.V. All rights reserved.