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

Abstract

Fe 3 O 4 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 6 10 27 cm 2 s 21 to 6.8 6 10 27 cm 2 s 21 and an increase of proton conductivity from 31 mS cm 21 to 78 mS cm 21 . 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 21 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.

Magnetic field alignment of stable proton-conducting channels in an electrolyte membrane

“…Ostensibly, a shorter and less tortuous conduction pathway in the TP direction would increase the efficiency of proton transport from the anode to the cathode, thereby increasing PEMFC performance. So far, efforts to orient conductivity in the TP direction have been explored by electric field alignment 9–15 and magnetic field alignment 16–20 . Electric field alignment has been explored by incorporating metal 9 or metal oxide 10 , non-solvent-assisted casting 11 , and polymer blends 12–15 , but improvements in both conductivity and fuel cell performance have been modest.…”

“…Electric field alignment has been explored by incorporating metal 9 or metal oxide 10 , non-solvent-assisted casting 11 , and polymer blends 12–15 , but improvements in both conductivity and fuel cell performance have been modest. In the case of magnetic field alignment, this has been carried out using materials related only to metal oxides, such as pristine metal oxides 16–18 , coated metal oxide 19 , and other filler deposited with metal oxide 20 . This class of fillers for magnetic alignment are not proton conductive, and thus their incorporation would result in a reduction in ion exchange capacity (IEC), which compromises any gains in proton conductivity through enhancement of TP alignment.…”

Potential carbon nanomaterials as additives for state-of-the-art Nafion electrolyte in proton-exchange membrane fuel cells: a concise review

“…The obtained high power density was ascribed to the improved proton conductivity as well as the methanol barrier properties of Im-CNT. Fe 3 O 4 -anchored Nafion-functionalized MWCNTs (MWCNT-MNP-Nafion) were prepared and incorporated into the Nafion matrix by Chang et al 132 The obtained MWCNT-MNP-Nafion/Nafion was highly effective in improving the DMFC power density from 12.5 mW cm −2 for bare Nafion to 92.4 mW cm −2 for the composite PEM. A further enhancement in DMFC power density was obtained by magnetically aligning the MWCNT-MNP-Nafion in the Nafion matrix.…”

Progress in neutron techniques: towards improved polymer electrolyte membranes for energy devices

“…To address these targets, the main strategies being implemented in academic and industry research laboratories worldwide are based on the development of: (i) new synthetic membranes, where careful design of chemical and physical properties is being used to tune channel size and distribution [34][35][36]; as well as (ii) formation of composite membranes, where the incorporation of fillers (e.g. silica, clay, zeolites, etc) into the Nafion membrane serves to increase the thermal, chemical and mechanical resistance while playing a role in managing water uptake, membrane swelling and ion transport [37][38][39][40]. Recent research is directed at introducing low-dimensional nanoporous materials including graphene oxide or graphitic carbon nitride into the polymeric matrix [4,[41][42][43] (figure 1), or by using metal organic framework membranes [44,45].…”