Sulfonated Graphene Oxide Platelets in Nafion Nanocomposite Membrane: Advantages for Application in Direct Methanol Fuel Cells

Abstract

Graphene oxide (GO) is well known as an excellent amphiphilic material due to its oxygen-containing functional groups and its chemical tunability. By intercalation chemistry, organo-modified GO containing sulfonilic terminal groups were prepared and used as nanoadditive in Nafion polymer for the creation of hybrid exfoliated composites. The incorporation of hydrophilic 2D platelike layers in the Nafion membranes is expected to induce advantages in terms of thermal stability and mechanical and barrier properties (limitation of the methanol crossover by increased tortuosity and obstruction effect), although it may negatively affect the proton conductivity. In this work, we show how different preparation methods of the nanocomposites influence morphology, transport properties, and barrier effect to methanol. The hybrid membranes are characterized by powder X-ray diffraction and microscopies (SEM, TEM, and AFM). Water and methanol transport properties inside the nanocomposites are investigated by NMR spectroscopy (diffusivity and relaxation times), unveiling a reduction of the methanol diffusion and, nevertheless, an increase in the proton mobility and water retention at high temperatures. Finally, the electrochemical properties are investigated by direct methanol fuel cell (DMFC) tests, showing a significant reduction of the ohmic losses at high temperatures, extending in this way the operating range of a DMFC.

An NMR study on the molecular dynamic and exchange effects in composite Nafion/sulfated titania membranes for PEMFCs

“…The proton signal is very wide, about 1 kHz, typical of solid-like configuration, due to the strong confinement of the water molecules within the hydrophilic pores. Clearly, this NMR peak is the convolution of "different" water signals (free and bound to the various hydrophilic groups) in fast rate of proton exchange [7,30]. By increasing temperature, the intensity of this peak decreases because of the water evaporation from the membranes.…”

Orderly sandwich-shaped graphene oxide/Nafion composite membranes for direct methanol fuel cells

“…On the contrary, it may cause some losses in proton conductivity. Although the protons released from the −OH and −COOH groups on the edge of GO nanosheets may contribute to the increment in the proton conductivity of the composite membranes and the acids/hydrophilic sites in GO may retain a certain amount of bound water [30,31]. …”

Polymer Nanocomposite Membranes of Sulfonated Poly(Styrene‐Isobutylene‐Styrene) With Sulfonated Graphene Oxide for Fuel Cell and Protective Clothing Applications

“…Such structures are more noticeable as the sulfonation level increases because more phase segregation occurs. Other AFM studies also suggest that sGO enchances the morphology , while GO leads to the formation of very homogeneous domains in the membrane . The addition of sGO enhanced the ionic domains and their interconnections, whereas GO incorporation increased the hydrophobic domain of SO 3 H SIBS.…”

“…In other similar studies with SPEEK, sGO/S-PEEK nanocomposite membranes presented lower methanol permeability and higher IEC, WU, and proton conductivity than Nafion ® [29,30]. Nicotera and coworkers modified Nafion ® with sGO varying the orientation of the filler in the membranes [31]. Their results suggested that the well-oriented fillers added tortuosity to the membrane producing a reduction in methanol permeation, but in some instances also reducing cell performance.…”