Abstract
Chitosan is one of the natural biopolymers that has been studied as an alternative material to replace Nafion membranes as proton change membranes. Nevertheless, unmodified chitosan membranes have limitations including low proton conductivity and mechanical stability. The aim of this work is to study the effect of modifying chitosan through polymer blending with different compositions and the addition of inorganic filler on the microstructure and physical properties of N-methylene phosphonic chitosan/poly (vinyl alcohol) (NMPC/PVA) composite membranes. In this work, the NMPC biopolymer and PVA polymer are used as host polymers to produce NMPC/PVA composite membranes with different compositions (30–70% NMPC content). Increasing NMPC content in the membranes increases their proton conductivity, and as NMPC/PVA-50 composite membrane demonstrates the highest conductivity (8.76 × 10−5 S cm−1 at room temperature), it is chosen to be the base membrane for modification by adding hygroscopic silicon dioxide (SiO2) filler into its membrane matrix. The loading of SiO2 filler is varied (0.5–10 wt.%) to study the influence of filler concentration on temperature-dependent proton conductivity of membranes. NMPC/PVA-SiO2 (4 wt.%) exhibits the highest proton conductivity of 5.08 × 10−4 S cm−1 at 100 °C. In conclusion, the study shows that chitosan can be modified to produce proton exchange membranes that demonstrate enhanced properties and performance with the addition of PVA and SiO2.
Highlights
Nafion membranes have been commercially used as proton exchange membranes (PEMs) due to their high proton conductivity under hydrated conditions and good thermal and chemical stability
This work proved that chitosan could be successfully modified through the phosphorylation process, which introduced phosphonic acid groups to convert chitosan into N-methylene phosphonic chitosan (NMPC)
This modification produced a watersoluble functionalized polymer that had a high degree of hydrophilicity compared to pristine chitosan, which is insoluble in water
Summary
Nafion membranes have been commercially used as proton exchange membranes (PEMs) due to their high proton conductivity under hydrated conditions and good thermal and chemical stability. Aside from these advantages, Nafion membranes still have several shortcomings, including the high-cost of its materials, intense methanol crossover, and a severely decreased proton conductivity under low humidity conditions [1]. The operation of PEMFC with the use of Nafion membrane was limited to low operating temperature (≈80 ◦ C) [2,3]. ◦ C, the affinity with water and mechanical stability of Nafion membrane will be reduced [3]. Various studies have been carried out over the years testing various biopolymer materials as alternative membrane materials to replace Nafion membranes
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