[ recycling ]
Fig 3 . Pyrometallurgical processing of PGM-containing materials
The greatest drawback is the fact that the current recycling process with hightemperature thermal treatment CANNOT be applied to PEM components , due to emission of notorious fluoro compounds . Moreover , the value of the polymer component can never be regained .
Fluoropolymers in MEA
A typical MEA has 25 – 50 % by weight composition of fluoropolymer ( Figure 4 ). 8 Fluoropolymers are ( 1 ) an excellent proton exchange polymer , perfluorinated sulfonic acid ( PFSA ), used as electrolyte ( function of proton conduction , electron insulation , preventing gas permeation , high chemical and mechanical stability , etc .) and ionomer in the catalyst layer ( to expand the reaction zone ); and ( 2 ) hydrophobic agents , polytetrafluoroethylene ( PTFE , or Teflon™ ) in the catalyst layer , microporous layer and gas diffusion layer for water management . This also means that even if the membrane itself is separated or replaced by a hydrocarbontype polymer , the remaining electrodes would still represent a large carrier of fluorine .
Severe emission from incineration of fluoropolymer has been well documented 9 by several groups . Gaseous fluoro compounds , generated from the burning of MEAs , have a global warming potential ( GWP ) of 10,000 to 22,000 times that of
CO 2
, which aggressively promotes the greenhouse effect .
MEA recycling using pyrometallurgy
Since PGMs from spent MEAs are still a very small stream of the secondary PGM resource , the current recycling process relies on the existing PGM recycling
30 Hydrogen Tech World | Issue 7 | December 2022