Effect of stress on dissolution/precipitation of platinum: Implications concerning core-shell catalysts and cathode degradation in proton exchange membrane fuel cells

摘要

Effect of applied stress on dissolution/precipitation of platinum was investigated. Two platinum wires/foils were partially immersed in a PtCl_4 solution in DMSO. A tensile load was applied to one wire/foil and the other one was left load free. The wire/foil subjected to a tensile load developed a positive potential (became cathodic) with respect to the unstressed wire/foil. This observation suggests that under a tensile stress, the chemical potential of Pt decreases. This result suggests design strategies for core-shell catalysts used in proton exchange membrane fuel cells (PEMFCs). Nanosize catalyst particles are under compression due to the Gibbs-Thompson effect. Core-shell catalysts have additional stresses in the shell depending upon lattice parameters of the core and the shell. The present results suggest that stable core-shell catalysts for PEMFC with Pt shell should be designed such that the shell is under a tensile stress (or reduced compression compared to monolithic catalyst particles). The present results also suggest that from the standpoint of stability, the lattice parameter of the core should be larger than that of the shell.