Dissolution of oxygen reduction electrocatalysts in an acidic environment: Density functional theory study

Density functional theory is employed to determine the reaction thermodynamics of a group of chemical and electrochemical reactions chosen to investigate the dissolution of metal atoms from oxygen reduction reaction catalysts in an acid medium. Once a set of thermodynamically allowed reactions is established, those reactions are selected to investigate the relative stabilities of Pt atoms and of other transition metal atoms (Ir, Pd, Rh, Ni, and Co) toward the dissolution reactions. The dissolution reactions that are found thermodynamically favorable are electrochemical and involve adsorbed oxygenated compounds that are intermediate species of the oxygen reduction reaction. Iridium is found to be the most stable among the various pure metals in comparison to Pt. Most of the metals alloyed with Pt cause a decrease of the Pt stability against dissolution, except for Ni, which does not affect it. On the other hand, the influence of Pt on the stability of the second metal in the alloy follows the same trend as in pure metal catalysts, with Ir being the most stable. When both atoms in a PtM alloy are involved in dissolution reactions, alloyed Ir is also found more stable than Pt in a given dissolution reaction, and the same behavior is found in alloyed Co for most of the reactions studied.