Environmentally Friendly Recycling of Fuel‐Cell Membrane Electrode Assemblies by Using Ionic Liquids

Abstract

The platinum nanoparticles used as the catalyst in proton exchange membrane fuel cells (PEMFCs) represent approximately 46 % of the total price of the cells for a large-scale production, and this is one of the barriers to their commercialization. Therefore, the recycling of the platinum catalyst could be the best alternative to limit the production costs of PEMFCs. The usual recovery routes for spent catalysts containing platinum are pyro-hydrometallurgical processes in which a calcination step is followed by aqua regia treatment, and these processes generate fumes and NO emissions, respectively. The electrochemical recovery route proposed here is more environmentally friendly, performed under "soft" temperature conditions, and does not result in any gas emissions. It consists of the coupling of the electrochemical leaching of platinum in chloride-based ionic liquids (ILs), followed by its electrodeposition. The leaching of platinum was studied in pure ILs and in ionic-liquid melts at different temperatures and with different chloride contents. Through the modulation of the composition of the ionic-liquid melts, it is possible to leach and electrodeposit the platinum from fuel-cell electrodes in a single-cell process under an inert or ambient atmosphere.

Recovery of Metals from Secondary Raw Materials by Coupled Electroleaching and Electrodeposition in Aqueous or Ionic Liquid Media

“…It has been previously shown that the anodic signal observed in BMIM Cl for potential values was higher than 1 V vs. Ag +I /Ag, and the oxidation peak A1 recorded in 0.25 M BMIM Cl in BMIM TFSI corresponded to both of the two following oxidation reactions (8) [35,36] and (9), whose occurrence cannot be distinguished from each other in the voltammograms: The cathodic stability was identical for the three electrolytes, and limited by the reduction of the BMIM + cation [34] at −1.5 V vs. Ag +I /Ag. We have previously demonstrated that Pt cannot be oxidized in BMIM TFSI [32]. The oxidation signal observed at 2.8 V vs. Ag +I /Ag in BMIM TFSI and in the IL mixture corresponds then to the oxidation of the TFSI − anion [34] (7):…”

“…1-butyl-3-methyl imidazolium bromide (BMIM Br) was prepared according to the procedure described in [31]. 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) was also prepared as reported in [32].…”

“…The platinum plate anode was weighed before and after its electrochemical dissolution, after rinsing with distilled water and acetone. A quantification method specific to ILs was developed in a previous work to determine platinum concentration by AAS [32]. All AAS measurements were conducted using a Varian ® AA 240 spectrometer, controlled with the SpectrAA© software (Agilent Technologies, Santa Clara, CA, USA).…”

“…We demonstrated previously the feasibility of anodic dissolution of platinum followed by its recovery by electrodeposition at a carbon cathode [32,33], using IL electrolytes at temperatures near 100 • C. The electrolyte was a mixture of two ILs having a common cation, BMIM + , associated with two different anions: Cl − and TFSI − . BMIM Cl was chosen due to the complexing property of chloride anions for platinum.…”

“…The cathodic stability was identical for the three electrolytes, and limited by the reduction of the BMIM + cation [34] at −1.5 V vs. Ag +I /Ag. We have previously demonstrated that Pt cannot be oxidized in BMIM TFSI [32]. The oxidation signal observed at 2.8 V vs. Ag +I /Ag in BMIM TFSI and in the IL mixture corresponds then to the oxidation of the TFSI − anion [34] (7):…”