Tuning surface hydrophilicity/hydrophobicity of hydrocarbon proton exchange membranes (PEMs)

Chenfeng He; Frej Mighri; Michael D Guiver; Serge Kaliaguine

doi:10.1016/j.jcis.2015.12.023

Tuning surface hydrophilicity/hydrophobicity of hydrocarbon proton exchange membranes (PEMs)

J Colloid Interface Sci. 2016 Mar 15:466:168-77. doi: 10.1016/j.jcis.2015.12.023. Epub 2015 Dec 14.

Authors

Chenfeng He¹, Frej Mighri¹, Michael D Guiver², Serge Kaliaguine³

Affiliations

¹ Department of Chemical Engineering, Laval University, Quebec, Quebec G1V 0A6, Canada.
² State Key Laboratory of Engines, Department of Mechanical Engineering, Tianjin University, Tianjin 300072, China; Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China. Electronic address: Michael.Guiver@outlook.com.
³ Department of Chemical Engineering, Laval University, Quebec, Quebec G1V 0A6, Canada. Electronic address: serge.kaliaguine@gch.ulaval.ca.

PMID: 26722798
DOI: 10.1016/j.jcis.2015.12.023

Abstract

The effect of annealing on the surface hydrophilicity of various representative classes of hydrocarbon-based proton exchange membranes (PEMs) is investigated. In all cases, a more hydrophilic membrane surface develops after annealing at elevated temperatures. The annealing time also had some influence, but in different ways depending on the class of PEM. Longer annealing times resulted in more hydrophilic membrane surfaces for copolymerized sulfonated poly(ether ether ketone) (SPEEK-HQ), while the opposite behavior occurred in sulfonated poly(aryl ether ether ketone) (Ph-SPEEK), sulfonated poly(aryl ether ether ketone ketone) (Ph-m-SPEEKK) and sulfonated poly (aryl ether ether nitrile) (SPAEEN-B). Increased surface hydrophilicity upon annealing results from ionic cluster decomposition, according to the "Eisenberg-Hird-Moore model" (EHM). The increased surface hydrophilicity is supported by contact angle (CA) measurements, and the cluster decomposition is auxiliarily supported by probing the level of atomic sulfur (sulfonic acid) within different surface depths using angle-dependent XPS as well as ATR-FTIR. Membrane acidification leads to more hydrophilic surfaces by elimination of the hydrogen bonding that occurs between strongly-bound residual solvent (dimethylacetamide, DMAc) and PEM sulfonic acid groups. The study of physicochemical tuning of surface hydrophilicity/hydrophobicity of PEMs by annealing and acidification provides insights for improving membrane electrode assembly (MEA) fabrication in fuel cell (FC).

Keywords: Acidification; Annealing; Cluster; Decomposition; Hydrocarbon proton exchange membranes (PEMs); Hydrophilicity; Hydrophobicity; Interface; Multiplet; Surface.