Effects of NaCl and Na2SO4 catholytes on efficiency and lifetime of an ozone production system consisting of a polymer electrolyte membrane and Pt electrodes were investigated. When 0.5 M NaCl catholyte was used, a current efficiency of 29% and a power efficiency of 76 kWh/kg-O-3 were achieved at an electrolysis current density of 0.5 A/cm(2). Accelerated degradation experiments revealed that the use of the NaCl catholyte kept the Pt anode surface clean and enabled long operation. The use of 0.5 M Na2SO4 catholyte caused formation of an amorphous PtO2 film on the Pt anode surface, and the efficiency and lifetime of the system were rapidly decreased. NaCl concentration dependence measurements indicate that NaCl concentration of higher than 0.085 M is required for stable operation of the system. The formation of amorphous PtO2 films probably degrades the catalytic activity of the Pt anode in O-3 formation reactions. From the dissolution rate of the Pt anode, lifetime of the system is estimated to be 5800 Ah. (C) 2012 Elsevier Ltd. All rights reserved.