Does power ultrasound affect Nafion® dispersions?

Michael Adamski; Nicolas Peressin; Steven Holdcroft; Bruno G Pollet

doi:10.1016/j.ultsonch.2019.104758

Does power ultrasound affect Nafion® dispersions?

Ultrason Sonochem. 2020 Jan:60:104758. doi: 10.1016/j.ultsonch.2019.104758. Epub 2019 Aug 31.

Authors

Michael Adamski¹, Nicolas Peressin¹, Steven Holdcroft¹, Bruno G Pollet²

Affiliations

¹ Holdcroft Research Group, Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
² Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway. Electronic address: bruno.g.pollet@ntnu.no.

PMID: 31505419
DOI: 10.1016/j.ultsonch.2019.104758

Abstract

The effect of low frequency power ultrasound on Nafion® ionomer used for fabricating proton exchange membrane fuel cell (PEMFC) and water electrolyzer (PEMWE) catalyst inks was investigated. In this study, a series of Nafion® dispersions having three concentrations (10, 5, and 2.5% w/v) were studied under various irradiation durations (t_us), at fixed ultrasonic frequency (f = 42 kHz) and ultrasonic power (P > 2 W), under either controlled or unregulated bulk solution temperature conditions using a laboratory ultrasonic cleaning bath. Viscosity (η), thermal degradation, and glass transition temperature (T_g) for all Nafion® dispersion samples was measured and compared to untreated Nafion® samples. In our conditions, it was found that power ultrasound lowered the viscosity of all tested Nafion® dispersion samples; whilst thermogravimetric and differential scanning calorimetry analyses showed that for all ultrasonically irradiated samples, a negligible overall polymer degradation and no obvious change in T_g was observed under controlled and unregulated bulk temperature conditions. It was found that it is possible that acoustic cavitation causes depolymerisation followed by a polymerisation initiation step during ultrasonication. By comparing the ultrasonically treated and high-shear mixed samples, it was also observed that acoustic and hydrodynamic cavitation played an important role in the reduction of dispersion viscosity.

Keywords: Catalyst ink; Cavitation; Ionomer; Nafion®; PEMFC; PEMWE; Power ultrasound.