Preparation and Properties of Tetramethyl Ammonium Hydroxide Modified Polyvinylidene Fluoride with Styrene Sulfonated Membranes†

doi:10.7503/cjcu20180042

Abstract

Abstract:

Poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid)(PVDF-g-PSSA) membranes were synthesized via grafting styrene onto PVDF and then sulfonation. The PVDF of N-methylpyrrolidone solvent was initially modified by ammonium tetramethyl hydroxide(TMAH) methanol solution, and then the modified PVDF membrane was made after volatiling solvent. The styrene was grafted to the modified PVDF membrane, which utilized benzoyl peroxide(BPO) as the initiator. The microstructures, morphologies and sulfur distribution in the membranes were characterized by Fourier transform infrared spectroscope(FTIR), scanning electron microscopy(SEM), and energy-dispersive X-ray spectroscopy(EDX). Meanwhile, the effects of the TMAH mass fraction in methanol on proton conductivities and methanol permeabilities were investigated. The results indicated that PVDF was dehydrofluorinated by TMAH and carbon-carbon double bonds were obtained. The styrene was successfully grafted onto the modified PVDF membrane; the sulfur distribution in the interior and exterior of the membrane was homogeneous. The proton conductivities and methanol permeabilities of the PVDF-g-PSSA membranes increased with the increasing of TMAH mass fraction in methanol solution. When the TMAH mass fraction in methanol solution was 25%, the proton conductivity of the PVDF-g-PSSA membrane was 1.28×10^-2 S/cm and the methanol permeability was 4.58×10^-7 cm²/s, respectively. The membranes exhibited good thermal stability up to approximately 195 ℃. The peak power density of direct methanol fuel cell(DMFC) with above membrane was 16.45 mW/cm².

Key words: Direct methanol fuel cell, Polyvinylidene fluoride, Tetramethyl ammonium hydroxide, Styrene

CLC Number:

O631
O646

TrendMD:

LIU Qi,GUO Guibao,AN Shengli,LIU Jinyan. Preparation and Properties of Tetramethyl Ammonium Hydroxide Modified Polyvinylidene Fluoride with Styrene Sulfonated Membranes^†[J]. Chem. J. Chinese Universities, 2018, 39(9): 2062.

Figures/Tables 15

Scheme 1 Schematic procedures of PVDF-g-PSSA

Fig.1 Relationship between the content of TMAH and degree of grating(DOG) of pretreated PVDF

Fig.2 Effect of grating reaction temperature on degree of grating of PVDF-g-PSSA membranes

Fig.3 Effect of grating reaction time on the degree of grating of PVDF-g-PSSA membranes

Fig.4 Effect of the concentration of styrene on the degree of grating of PVDF-g-PSSA membranes

Fig.5 Effect of the concentration of BPO on the degree of grating of PVDF-g-PSSA membranes

Fig.6 Impendence of PVDF-g-PSSA membrane

Fig.7 Effects of TMAH consumption on conductivity(A) and ion exchange capacity(B) of PVDF-g-PSSA membranes

Table 1 Measurent results of the yield strength(δ), elongation at break(ε), swelling degree and water uptake of samples

Sample	δ/MPa	ε(%)	SD(%)	WU(%)
Nafion117	10.40	38.8	19.2	24.3
TMAH-10	13.42	43.8	6.4	9.3
TMAH-15	16.85	40.4	13.2	16.2
TMAH-20	18.67	37.4	15.3	25.4
TMAH-25	21.29	34.6	18.3	32.1
TMAH-30	14.12	36.4	21.2	37.8

Fig.8 IR spectra of PVDF(a), g-PVDF-M(b), PVDF-g-PS(c) and PVDF-g-PSSA(d) membranes

Fig.9 Wide-scan XPS spectra of PVDF(A) and PVDF-g-PSSA(B) membranes

Fig.10 SEM images of PVDF-g-PSSA membrane(A, B)and distribution of fluorine(C) and sulfur(D) on the surface of the cross-section of the membrane measured by EDX (A) Surface of PVDF-g-PSSA membrane; (B) cross-section of PVDF-g-PSSA membrane.

Fig.11 TGA curves of PVDF(a) and PVDF-g-PSSA(b) membranes

Fig.12 Effect of TMAH consumption on methanol permeability of PVDF-g-PSSA

Fig.13 Performance of single cell with PVDF-g-PSSA membrane(TMAH-25)

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