Synthesis of Tailored Perfluoro Unsaturated Monomers for Potential Applications in Proton Exchange Membrane Preparation.

Antonio Monopoli,Angelo Nacci,Fabio Palumbo,Francesco Fracassi,Pietro Cotugno,Michele Casiello,Antonella Milella

doi:10.3390/molecules26185592

Abstract

The aim of the present work is the synthesis and characterization of new perfluorinated monomers bearing, similarly to Nafion®, acidic groups for proton transport for potential and future applications in proton exchange membrane (PEM) fuel cells. To this end, we focused our attention on the synthesis of various molecules with (i) sufficient volatility to be used in vacuum polymerization techniques (e.g., PECVD)), (ii) sulfonic, phosphonic, or carboxylic acid functionalities for proton transport capacity of the resulting membrane, (iii) both aliphatic and aromatic perfluorinated tags to diversify the membrane polarity with respect to Nafion®, and (iv) a double bond to facilitate the polymerization under vacuum giving a preferential way for the chain growth of the polymer. A retrosynthetic approach persuaded us to attempt three main synthetic strategies: (a) organometallic Heck-type cross-coupling, (b) nucleophilic displacement, and (c) Wittig–Horner reaction (carbanion approach). Preliminary results on the plasma deposition of a polymeric film are also presented. The variation of plasma conditions allowed us to point out that the film prepared in the mildest settings (20 W) shows the maximum monomer retention in its structure. In this condition, plasma polymerization likely occurs mainly by rupture of the π bond in the monomer molecule.

Highlights

We focused our attention on the synthesis of various molecules with (i) sufficient volatility to be used in vacuum polymerization techniques (e.g., plasma-enhanced chemical vapor deposition (PECVD))), (ii) sulfonic, phosphonic, or carboxylic acid functionalities for proton transport capacity of the resulting membrane, (iii) both aliphatic and aromatic perfluorinated tags to diversify the membrane polarity with respect to Nafion®, and (iv) a double bond to facilitate the polymerization under vacuum giving a preferential way for the chain growth of the polymer
Proton exchange membrane fuel cells (PEMFCs), referred as solid polymer fuel cells, are the simplest type of fuel cells, with application spanning from portable power to automotive [1,2,3]
PEMFCs employ a membrane constituted by a perfluorinated polymer bearing acidic groups, working both as an electronic insulator and as a proton conductor

Summary

Introduction

Proton exchange membrane fuel cells (PEMFCs), referred as solid polymer fuel cells, are the simplest type of fuel cells, with application spanning from portable power to automotive [1,2,3]. The main drawback of Nafion® polymers is due to the membrane hydration, which still represents an operative limit for fuel cells, since the temperature must be maintained below 100 ◦C [6]. Another factor still limiting the commercial availability of PEMFCs is the cost associated to the active materials employed for their fabrication, i.e., Pt-based catalyst and the Nafion® membrane [6,7,8]. Only a few efforts have been made in the direction of finding a valid alternative to Nafion® [5,13,14]

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