Synthesis of Moderate Water-Uptake and Low Methanol Permeable Polymer Electrolyte Membrane from Functionalized Polyisoprene Impregnated Carbon Nanotubes

Christopher A Idibie

doi:10.11648/j.ijmsa.20180701.12

Abstract

The study of the synthesis of polymer electrolyte membrane exhibiting moderate water uptake and low methanol permeation for fuel cell application using functionalized polyisoprene impregnated with carbon nanotubes (CNTs) was carried out. The functionalization of the polymer with chlorosulphonic acid of different initial concentrations of 0.0013, 0.001, 0.0017, and 0.0023 mol/L at the minimum time of 1hr produced ion exchange capacities (IEC) of 1.22, 1.92, 2.74, and 4.92 mmol/g, respectively, and at the maximum sulphonation time of 18hrs the IEC were 7.74, 8.78, 11.10, and 16.93 mmol/g, respectively. Their corresponding degrees of sulphonation (DS) for 1hr were 3.53, 5.55, 7.91, and 14.21%, respectively, and while at 18hrs their corresponding DS were 22.35, 25.37, 32.04, and 48.88%, respectively, which implies that IEC and DS are directly proportional to the concentration of acid used and reaction time. Result also showed that synthesized membrane without carbon nanotubes absorbed so much of it weight in water; 31.34 and 73.97% of its weight in both 1 day and 6 days for membrane with 48.88% DS. Whereas the membrane that was impregnated with CNTs of the same DS exhibited a lesser absorption of 23.23 and 53.23% of its weight in both 1 day and 6 days, thereby reducing the high water uptake of the membrane that would have affected it negatively by 1.3 fold. Apart from the conductivity of the synthesized membrane witnessing an increase by 1 order with the membrane impregnated with CNTs from 10<sup>-3</sup> S/cm to 10<sup>-2</sup> S/cm, it was also found out that the methanol crossover was lower than that of commercial Nafion, where membrane impregnated with CNTs had methanol crossover improvement with a difference of 0.48 Mol/L over its counterpart without CNTs as a result of the presence of CNTs.

Highlights

Fuel cells which are recognized as viable and promising alternative energy sources to fossil fuel [1, 2] require the central component being the polymer electrolyte membrane (PEM) to function [3, 4]
Comparing the likes of direct methanol fuel cell (DMFC) to the conventional H2/O2 fuel cell, DMFCs in particular are attractive for several applications as a result of their lower weight and volume compared with indirect fuel cells; the major challenge associated with it is the loss of fuel due to the permeation of methanol across the Nafion membrane [8]
Reaction scheme represents the reaction of polyisoprene in chlorosulphonic acid medium

Summary

Introduction

Fuel cells which are recognized as viable and promising alternative energy sources to fossil fuel [1, 2] require the central component being the polymer electrolyte membrane (PEM) to function [3, 4]. Water molecules are necessary in the membrane because it provides the medium for the movement of ions, but excess uptake of water results in swelling of the membrane and which affect the mechanical and conductivity properties [5] In another vein, methanol permeation through polymer electrolyte membrane (PEM) is recognized as a major problem and constraint against large scale commercialization of fuel cell, especially direct methanol fuel cell (DMFC) for energy generation [5] Fuel cells such as proton exchange membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) are known to have proton-conducting pathways produced by fixed functional groups or proton conducting gel [6]. Effort to functionalize polyisoprene through sulphonation and impregnation of carbon nanotubes (CNTs) will be carried out and study for its water absorption and methanol crossover abilities, in an effort of getting an alternative PEM

Results

Discussion

Conclusion