A synthesis study of phosphonated PSEBS for high temperature proton exchange membrane fuel cells

Abstract

A series of novel phosphonated proton exchange membranes has been prepared using poly(styrene‐ethylene/butylene‐styrene) block copolymer (PSEBS) as base material. Phosphonic acid functionalization of the polymer was performed by a simple two‐step process, via chloromethylation of PSEBS followed by phosphonation utilizing the Michaels–Arbuzov reaction. The successful phosphonation of the polymers were characterized by NMR and Fourier transform infrared. The phosphonated ester form of the membranes were obtained by solvent evaporation method and hydrolyzed to get a proton conducting membrane. The membrane properties such as ion exchange capacity, water uptake and proton conductivity at various temperatures were examined for their suitability to be utilized as a high temperature polymer electrolyte. Additionally, the morphology, thermal, and mechanical properties of the synthesized membranes were investigated, using scanning electron microscope, thermogravimetric analysis, and tensile test, respectively. The effective (anhydrous) proton conductivity was studied with respect to various degrees of functionalization. From the studies, the membranes were found to have a comparatively good conductivity and one of the membranes reached the maximum value of 5.81 mS/cm2 at 140 °C as measured by impedance analyzer. It was found that the synthesized membranes were mechanically durable, chemically, and thermally stable. Hence, the synthesized phosphonated membranes could be a promising candidate for high temperature polymer electrolyte fuel cell applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45954.

A parametric analysis on PEFCs for high-temperature applications

“…Where L is the thickness, R is the resistance, and A is the surface area between membrane and electrode [9].…”

“…From these factors listed IEC is an essential factor in determining the proton conductivity of a membrane, it is a measure of the molar equivalents of ion conductors available per unit mass of the dry polymer membrane [16]. In general, a higher IEC is required to achieve high proton conductivity (e.g., IEC > 2.0 meq/g) is generally required [15].…”

“…A more tangible relationship for characterising a polymer for its use in a specific application is the effect of the degree of membrane phosphonation (DP) on the IEC of the polymer. poly(styrene-ethylene-butylene-styrene) (Poly(S-E-B-S)) which both achieved moderately high conductivity in an appropriate temperature range according to their respective studies [27,9]. Poly(sulfone) (27) Fluorinated Copolymers [33] In the study undertaken by Parvole and Jannasch [26], Poly(sulfones) had side chains of poly(vinyl phosphonic acid) (PVPA) grafted to them.…”

“…Poly(sulfone) with up to 57wt% PVPA was measured, they found this to have the highest IEC at 5.3meq/g. This study found that in general the higher weight percentage of the polymer that was PVPA the higher the IEC of the membrane and hence the higher the proton conductivity of the membrane, this result provides positive affirmation to the trend seen in the data of Fig 5. Elumalai et al [9] explored multiple different degrees of phosphonated Poly(S-E-B-S), these were constructed and tested at 140°C. Their study found that 54% phosphonated P(S-E-B-S) achieved the highest proton conductivity at this temperature of 5.81mS/cm, they concluded that the IEC of the membranes increases with increasing degree of phosphonation of the membrane, and hence the proton conductivity increases.…”

The Synthesis of Poly(Vinyl Alcohol) Grafted with Fluorinated Protic Ionic Liquids Containing Sulfo Functional Groups

“…Over the years, researchers have been developing the functionalization of polymer materials by applying various approaches, including synthesis, grafting, crosslinking, and polymerization [ 3 , 7 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Such modification methods result in the formation of chemical bonds between the polymer and the modifying agent.…”