Dissolution of platinum in acidic media

To understand the degradation of the Pt/C cathode for use in polymer electrolyte fuel cells, the solubility and the dissolution mechanism of platinum in acidic media was very important fundamentally. In this study, the platinum solubility has been determined in acidic electrolytes as a function of temperature and pH. The solubility was 3 × 10−6 mol dm−3 at 25 °C in 1 mol dm−3 of H2SO4, HClO4, and CF3SO3H under air. It increased at higher temperature and decreased in pH. The apparent enthalpy of the dissolution reaction was ca. 25 kJ mol−1, and the solubility was proportional to [H+] in these acids. The platinum solubility in oxygen was slightly higher than that in air. The detected dissolved Pt species was 4 valent. On the other hand, the solubility of platinum in nitrogen was much lower than the oxygen-containing atmosphere. Based on these results, the platinum solubility in an oxygen-containing atmosphere would mainly be the following acidic dissolution reaction: PtO2 + H+ + H2O = Pt(OH)3+.