The influence of oxygen atmosphere on platinum (Pt) dissolution under potentiodynamic conditions was investigated in 1.0 mol dm(-3) HClO4 at 80 degrees C over the range 0.0-0.7 MPa of oxygen partial pressure (p(O2)). The rate of Pt dissolution depended concavely on p(O2) with the minimum at 0.091 MPa. When p(O2) was below 0.091 MPa, the oxygen atmosphere suppressed the platinum dissolution from an oxide-deprived Pt surface owing to an increase in the coverage of passive oxides, resulting in a decrease in the rate of Pt dissolution with increasing values of p(O2). For p(O2) >= 0.091 MPa, the current of oxygen reduction reaction (ORR) increases with p(O2). This further participated in an increase in the rate of Pt dissolution, probably through the cathodic dissolution of higher-order oxides formed as intermediates in ORR. (C) 2013 The Electrochemical Society.