Hydrogen is one of the most promising energy carriers. Currently, the most used technology to produce electricity from hydrogen, particularly for green mobility, is the technology based on the use of Proton Exchange Membrane Fuel Cells (PEMFC). Platinum, pure or alloyed with another element, remains essential in the design of efficient catalysts either for anode or cathode catalytic layer in PEMFC. This metal is rare and expensive hence recycling it becomes an important issue for the hydrogen sector development.

Chemical ways to recover platinum from PEMFC have been already studied ^1-2 based on Pt leaching using either a mix of HCl/HNO₃ or HCl/H₂O₂. In our project, we investigate an electrochemical process to leach platinum contained in aged Pt based catalysts to further resynthesize catalysts from the recovered Pt salts. The electrodissolution of platinum becomes significant with the oxidation of the metal (around 1.1 V vs RHE) but particularly when the oxidized platinum is reduced (around 0.7 V vs RHE) ³. Moreover, the dissolution is enhanced when a complexing agent as chloride anion is introduced ⁴. The idea of our process is to study the impact of different protocol of steps between high potential (to oxidize platinum) and low potential (to reduce platinum oxide). The improvement of the process is linked to the upper and lower potential values, the number of steps and the nature of the electrolyte and the complexing agent. Our main parameter to monitor the dissolution is the changes in electrochemical real surface area (ECSA) associated to transmission electron microscopy (TEM) images of the catalyst at different stages of the protocol as illustrated in Figure 1.

In terms of methodology a model study on fresh commercial Pt/C catalyst has been first performed to determinate the optimal conditions of Pt dissolution followed by the application of the protocol on membrane electrode assemblies (MEA) aged in real conditions.

¹ L. Duclos, L. Svecova, V. Laforest, G. Mandil, et P.-X. Thivel, « Process development and optimization for platinum recovery from PEM fuel cell catalyst », Hydrometallurgy, vol. 160, p. 79‑89, mars 2016, doi: 10.1016/j.hydromet.2015.12.013.
² L. Duclos, M. Lupsea, G. Mandil, L. Svecova, P.-X. Thivel, et V. Laforest, « Environmental assessment of proton exchange membrane fuel cell platinum catalyst recycling », J. Clean. Prod., vol. 142, p. 2618‑2628, janv. 2017, doi: 10.1016/j.jclepro.2016.10.197.
³ S. Cherevko, A. R. Zeradjanin, G. P. Keeley, et K. J. J. Mayrhofer, « A Comparative Study on Gold and Platinum Dissolution in Acidic and Alkaline Media », J. Electrochem. Soc., vol. 161, n° 12, p. H822‑H830, 2014, doi: 10.1149/2.0881412jes.
⁴ S. Geiger, S. Cherevko, et K. J. J. Mayrhofer, « Dissolution of Platinum in Presence of Chloride Traces », Electrochimica Acta, vol. 179, p. 24‑31, oct. 2015, doi: 10.1016/j.electacta.2015.03.059.