Dissolution Rate of Noble Metals for Electrochemical Recycle in Polymer Electrolyte Fuel Cells

An electrochemical recycling process of the noble metal such as Pt and Ru from the membrane electrode assemblies (MEAs) in fuel cells was investigated for the environment-friendly process without aqua regia. The dissolution rate of Pt in HCl solution was about 50 times as fast as those in H2SO4 and HClO4 solutions. The Pt dissolution rate increased linearly with HCl concentration. Pt dissolution under fluctuating potential using saw-tooth wave is 15 times faster than that under constant potentials. The electrochemical dissolution method can also be applied to the dissolution of Pt and Ru in the PtRu catalysts. The chemical methods using aqua regia, HCl-H2O2 mixed solution, and HCl only were also investigated for the comparison as the electrochemical methods. The Pt dissolution rate decreased according to the order of aqua regia > 11.3 M HCl-0.36 M H2O2 > 1 M HCl-10.3 M H2O2 > 1 M HCl. The vaporization rate of oxidants (NOCl and Cl2) from aqua regia at 333 K was 40 times as fast as that at 298 K by a spectrochemical method.