Hsieh-Yu Li

Nafion-functionalized electrospun poly(vinylidene fluoride) (PVDF) nanofibers for high performance proton exchange membranes in fuel cells

Nafion-functionalized poly(vinylidene fluoride) electrospun nanofibers (PVDFNF-Nafion) have been prepared through a 3-step reaction route. The chemical structure of PVDFNF-Nafion is characterized with Fourier transform infrared and X-ray photoelectron spectroscopy. Functionalization with Nafion chains improves the interfacial compatibility between the PVDF-based nanofibers and Nafion matrix in formation of PVDFNF-Nafion reinforced Nafion composite membrane (Nafion-CM1). Aggregation of Nafion chains on the nanofiber surfaces induces the formation of proton-conducting channels so as to increase the proton conductivity of the Nafion-CM1 membrane. In the H2/O2 single cell test, Nafion-CM1 shows a maximum power density of 700 mW cm−2 which is higher than the value of 500 mW cm−2 recorded with commercial Nafion 212 membrane. The presence of PVDFNF-Nafion also depresses the methanol permeability of the Nafion-CM1 membrane with alteration of the crystalline domains of Nafion. In direct methanol fuel cell tests, the low methanol permeability of Nafion-CM1 means it could be operated with 5 M methanol as the fuel and exhibits a maximum power density of 122 mW cm−2, which is larger than the value (60 mW cm−2) recorded with commercial Nafion 117 membrane and 2 M methanol fuel.

Polyelectrolyte composite membranes of polybenzimidazole and crosslinked polybenzimidazole-polybenzoxazine electrospun nanofibers for proton exchange membrane fuel cells

Polybenzoxazine (PBz)-modified polybenzimidazole (PBI) nanofibers have been prepared by an electrospinning process. The nanofibers have been crosslinked through the ring-opening addition reaction of the benzoxazine groups of PBz. The crosslinked PBI nanofibers show an enhancement in mechanical strength and an increase in resistance to solvents, so are of use as a reinforcement for the preparation of PBI-based composite membranes. Modification of the PBI-based composite membranes with the crosslinked PBI nanofibers significantly improves their mechanical properties, acid uptakes, and dimensional stability upon acid doping. The composite membrane shows a proton conductivity of 0.17 S cm−1 at 160 °C under anhydrous conditions, which is about 2-fold higher compared to the proton conductivity of the neat PBI membrane. The single cell employing the composite PBI membrane exhibits a maximum power density of 670 mW cm−2, which is about a 34% increase compared to the cell employing the neat PBI membrane. A convenient and effective approach to prepare high performance proton-exchange membranes for high temperature fuel cells has been demonstrated.

Poly(lactide)-functionalized and Fe3O4 nanoparticle-decorated multiwalled carbon nanotubes for preparation of electrically-conductive and magnetic poly(lactide) films and electrospun nanofibers

Polymer-functionalized magnetic multiwalled carbon nanotubes (MWCNTs) have been prepared by a 2-step process. Fe3O4 nanoparticles are first decorated onto MWCNTs through Diels–Alder reaction. The resulting magnetic MWCNTs have been functionalized with polymers through an ozone-mediated process, which is able to incorporate kinds of matrix polymers to the magnetic MWCNTs. Poly(lactide)-functionalized magnetic MWCNTs (mCNT–PLA) have been prepared in this work for preparation of electrically-conductive and magnetic poly(lactide)/MWCNTs composite films and electrospun fibers. The magnetic and electrically-conductive feature of the functionalized MWCNTs helps to the formation of nanofibers in the electrospinning process of poly(lactide). The nanofibers possessing 0.3 wt% of mCNT–PLA exhibit a Youngs modulus and an elongation at break of 25 MPa and 150%, respectively. Compared to the values of 9 MPa and 12% shown with the neat PLA electrospun fibers, the presence of mCNT–PLA not only strengthens but also toughens the PLA-based electrospun fibers.

Nanocomposite membranes of Nafion and Fe3O4-anchored and Nafion-functionalized multiwalled carbon nanotubes exhibiting high proton conductivity and low methanol permeability for direct methanol fuel cells

Fe3O4 magnetic nanoparticle-anchored and Nafion-functionalized multiwalled carbon nanotubes (MWCNT–MNP–Nafion) have been prepared and used as a nano-additive for Nafion. The addition of 0.1 wt% of MWCNT–MNP–Nafion to Nafion results in the membranes showing a reduction of methanol permeability from 30.1 × 10−7 cm2 s−1 to 6.8 × 10−7 cm2 s−1 and an increase of proton conductivity from 31 mS cm−1 to 78 mS cm−1. The presence of MWCNT–MNP–Nafion reduces the ionic cluster sizes and decreases the free volume element concentration of the modified Nafion membrane. Both have been verified with small angle X-ray scattering spectroscopy and positron annihilation lifetime spectroscopy and contribute to the reduction of the methanol permeability of the membrane. The increase in the proton conductivity originates from the formation of proton-conducting pathways on the MWCNT bundles. For the membrane fabricated under a magnetic field, its proton conductivity further increases to 85 mS cm−1 due to the magnetically-driven alignment of MWCNT–MNP–Nafion in the Nafion matrix (A-Nafion-NM-0.1). Compared to the plain recast Nafion membrane, the A-Nafion-NM-0.1 membrane has a 15-fold membrane selectivity, an 8.7-fold maximum power density, and a 6.6-fold current density at an operating voltage of 0.4 V in the tests for direct methanol fuel cells (DMFC). The high performance of the membrane in the DMFC tests demonstrates that the MWCNT–MNP–Nafion is a highly efficient additive for the preparation of Nafion-based membranes for DMFCs.