We systematically analyzed the formation energy and solvation free energy of four- and six-coordinate Pt(II) and Pt(IV) complexes with three types of ligands (H2O, OH-, and HSO4-) in concentrated sulfuric acid to rationalize the Pt electrocatalyst degradation and dissolution mechanisms as a model for a polymer electrolyte fuel cell. Because the formation energy and solvation free energy of Pt(IV) complexes are larger than those of Pt(II) complexes, the Pt(IV) complexes are more probable as the dissolved Pt species than Pt(II). The local relaxations about atomic charges and geometry by the substitution of OH- or HSO4- for H2O are one of the factors influencing the stability of dissolved Pt complex. We predict the [Pt(H2O)2(OH)4] and [Pt(OH)4]2- are important complexes for desorption from the Pt surface based on the desorption energy analysis of Pt complex from the Pt surface. The [Pt(H2O)4]2+ complex, which is formed by a reduction reaction from Pt(IV) and a proton addition reaction, shows the possibility of the final form before reprecipitation on the Pt surface. We theoretically estimated the Pt dissolution and reprecipitation mechanisms from an atomistic view.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films