Impact of CeO2 Nanofiller on the Physicochemical Properties, Conductivity Mechanism and Tolerance to Radical-Induced Degradation of Hybrid Inorganic-Organic Proton-Exchange Membranes Based on an Aquivion™ Matrix
Authors: Di Noto Vito , Silvestri Federica , Negro Enrico , Vezzù Keti , Pagot Gioele 
Published: December 2024

Proton exchange membrane fuel cells (PEMFCs) are electrochemical energy conversion devices that are playing a pivotal role in today’s energy transition away from fossil fuels [1]. The proton exchange membrane (PEM) at the heart of each PEMFC modulates key performance features such as the power density of the device. The PEM also contributes heavily to set the durability level of the entire PEMFC. State-of-the-art PEMs consist of perfluorinated ionomers functionalized with perfluoroethereal side chains terminated with highly acidic –SO3H groups. There are several different families of perfluorinated ionomers for implementation in PEMs, that are mainly distinguished on the basis of the chemical nature of the perfluoroethereal side chains and of their density along the backbone. A few examples of such ionomers include Nafion™, Aquivion™, Flemion™ and other macromolecules devised by 3M and Asashi. All these ionomers exhibit a high chemical, thermal and mechanical stability and a good proton conductivity at high hydration levels [2].

One of the main mechanisms on the basis of the loss of performance in PEMFCs is the degradation of the PEM prompted by radicals. The latter are formed as byproducts of the electrode processes upon PEMFC operation [3]. The negative effect of radicals on PEMs can be mitigated by the introduction of dopants, that act as radical scavengers [4]. In this work, a new family of hybrid inorganic-organic PEMs is presented, consisting of an Aquivion™ matrix dispersing CeO2 nanopowders. The PEMs undergo an extensive physicochemical characterization to study their ion-exchange capacity (IEC), thermal properties, morphology and structure. The electrical response of the PEMs is examined in detail by means of broadband electrical spectroscopy (BES). The resulting information is integrated to elucidate the long-range charge migration mechanism. The PEMs are studied: (i) as a function of hydration; and (ii) both in the pristine state and upon treatment with Fenton’s reagent. This allows to obtain a comprehensive picture on how the introduction of the CeO2 nanofiller: (i) affects the mesoscale features of the Aquivion™ matrix; and (ii) mitigates the degradation phenomena triggered by the exposure of the PEM to radicals.

References

[1] N. Alonso-Vante, V. Di Noto, Electrocatalysis for Membrane Fuel Cells: Methods, Modeling, and Applications
, Wiley (2023), ISBN: 978-352783057-2.

[2] P. Sgarbossa, V. Di Noto et al., Membranes for Fuel Cells, published in Electrocatalysis for Membrane Fuel Cells - Methods, Modelling and Applications; Wiley (2023).

[3] X. Luo et al., Int. J. Hydrogen Energy 40 (2015) 16714.

[4] Z. Wang et al., J. Membr. Sci. 421 (2012) 201.

Acknowledgements

This work has been supported under: (a) the National Recovery and Resilience Plan (NRRP), funded by the European Union - NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033 of June 17, 2022, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels”]; and (b) the project PERMANENT financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5.