Study On Bio-inspired Preparation Of DMFC Membranes And Proton Conductivity

Aiming at improving the proton conductivity of the novel DMFC membranes, bio-inspired methods, including biomimetic mineralization and mimicking proton pump on the purple membrane, were employed to fabricate organic/inorganic hybrid proton conductive membranes. The effects of the physical and chemical structure of the inorganic filler particles on the proton conductive capacity of the resultant membranes were studied systematically.In the first section, biomimetic mineralized hydroxyapatite (BHA) particles were synthesized using chondroitin sulfate as the template and catalyst. The particles were than incorporated into the chitosan (CS) matrix to fabricate CS/BHA hybrid membranes. The BHA particles in the membranes were stable even under the acidic condition. The thermal stability and hydrophilicity of the membranes were enhanced and the free volume characteristics were improved, simultaneously. When the BHA content was 8%, the proton conductivity of the membrane was 1.46×10-2 S·cm^-1 which was 127% higher than that of the pure CS membrane. The selectivity of CS/BHA-8% was 2.8 times as high as the pure CS membrane.The bacteriorhodopsin protein on the purple membrane of halobacteria uses acid amino acid residues as the proton conductive groups and the efficiency of proton transfer is enhanced by the synergistic effect of acid-base pair. Inspired by this mechanism, the hybrid membranes were prepared using flake-like and needle-like zirconium glyphosate (fZrG and nZrG) particles with sequential glycine residues as the fillers and alkaline CS as the bulk matrix. The fZrG and nZrG particles distributed uniformly within the membranes, the thermal stability as well as the methanol resistance of the membranes were enhanced simultaneously. The CS/nZrG membranes exhibited higher proton conductivity but lower methanol resistance compared to the CS/fZrG membranes. The proton conductivity of the CS/fZrG-20% and CS/nZrG^-15% membranes were 5.48×10-3 S·cm^-1 and 6.32×10-3S·cm^-1, respectively. The CS/nZrG-20% membrane displayed a selectivity which is 73.6% higher than the pure CS membrane.In order to develop proton conductive membranes with high mechanical and chemical stability, the ZrG particles were incorporated into sulfonated polyether ether ketone (SPEEK) matrix to fabricate SPEEK/ZrG hybrid membranes. SPEEK membranes with zirconium phosphate particles (SPEEK/ZrP) were fabricated for the comparison purpose. The incorporation of the ZrG and ZrP particles decrease the swelling and methanol crossover of the membraness. At 60 oC, the proton conductivity of the SPEEK/ZrG-8% membrane was 18.3% and 56.5% higher than that of the SPEEK/ZrP and SPEEK membranes, respectively. The SPEEK/ZrG membranes exhibited the potential of the DMFC application.