Chitosan/titanate Nanotube Hybrid Membrane with Low Methanol Crossover for Direct Methanol Fuel Cells

Titanate nanotubes (TNTs) about 10 nm in diameter and 200–600 nm in length were hydrothermally synthesized, and then incorporated into a chitosan (CS) matrix to fabricate chitosan/titanate nanotube (CS/TNT) hybrid membranes for a direct methanol fuel cell (DMFC). These hybrid membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), thermogravimetry (TG), and positron annihilation lifetime spectroscopy (PALS). Moreover, their performances, including mechanical strength, water and methanol uptake, methanol permeability, and proton conductivity were determined. SEM results demonstrated that TNTs dispersed homogeneously in the hybrid membranes. Mechanical strength and TG measurements demonstrated that the mechanical and thermal stability of CS/TNT hybrid membranes were much higher than those of pure chitosan membranes. PALS analysis revealed that the fractional free volume (FFV) of CS/TNT hybrid membranes increased with the incorporation of TNTs and, thus, resulting in the reduction of methanol crossover. In all as-prepared membranes, the hybrid membrane containing 15 wt % TNTs exhibited the highest mechanical strength of 85.0 MPa, low methanol permeability of 0.497 · 10^–6 cm²·s^–1, and proton conductivity of 0.0151 S·cm^–1, which had the potential for DMFC applications.