Mun-Sik Shin

Interactions between Multiwall Carbon Nanotubes and Poly(diallyl dimethylammonium) Chloride: Effect of the Presence of a Surfactant

The interactions between multiwall carbon nanotubes (MWCNTs) and poly(diallyl dimethylammonium) chloride (PDDA) have been studied in the presence of different ionic and nonionic surfactants, such as sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), Tween 20, 40, 60, and 80, and Triton X-100. On the basis of scanning electron microscopy (SEM) results, the MWCNT/PDDA sample treated with Triton X-100 has been observed to show good dispersion of nanotubes. This is due to the π-π stacking between the benzene ring of Triton X-100 and the hexagonal carbon rings of nanotubes and better coating of PDDA on MWCNTs, as is confirmed by the Raman studies. Energy dispersive X-ray (EDX) spectroscopic data shows the presence of higher oxygen content in the MWCNTs/PDDA/Triton X-100 sample. The maximum upshift in the C1s peak position and down-shift in the N1s peak position for the MWCNTs/PDDA/Triton X-100 sample has been observed from X-ray photoelectron spectroscopy (XPS) results and is due to the intermolecular charge transfer from carbon in MWCNTs to nitrogen in PDDA. The presence and nature of a surfactant in the MWCNTs/PDDA system has been found to affect their interactions. The above results suggest that the MWCNTs/PDDA/Triton X-100 system is suitable as a metal-free electrocatalyst for the oxygen reduction reaction (ORR) in fuel cells.

A study on the effect of different chemical routes on functionalization of MWCNTs by various groups (-COOH, -SO3H, -PO3H2).

Pristine multiwall carbon nanotubes [MWCNTs] have been functionalized with various groups (-COOH, -SO3H, -PO3H2) using different single- and double-step chemical routes. Various chemical treatments were given to MWCNTs using hydrochloric, nitric, phosphoric, and sulphuric acids, followed by a microwave treatment. The effect of the various chemical treatments and the dispersion using a surfactant via ultrasonication on the functionalization of MWCNTs has been studied. The results obtained have been compared with pristine MWCNTs. Scanning electron microscopy, energy dispersive X-ray [EDX] spectroscopy, and transmission electron microscopy confirm the dispersion and functionalization of MWCNTs. Their extent of functionalization with -SO3H and -PO3H2 groups from the EDX spectra has been observed to be higher for the samples functionalized with a double-step chemical route and a single-step chemical route, respectively. The ID/IG ratio calculated from Raman data shows a maximum defect concentration for the sample functionalized with the single-step chemical treatment using nitric acid. The dispersion of MWCNTs with the surfactant, Triton X-100, via ultrasonication helps in their unbundling, but the extent of functionalization mainly depends on the chemical route followed for their treatment. The functionalized carbon nanotubes can be used in proton conducting membranes for fuel cells.

Effect of Annealing of Nafion Recast Membranes Containing Ionic Liquids

The composite membranes comprising of sulfonated polymers as matrix and ionic liquids as ion-conducting medium in replacement of water are studied to investigate the effect of annealing of the sulfonated polymers. The polymeric membranes are prepared on recast Nafion containing the ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (). The composite membranes are characterized by thermogravitational analyses, ion conductivity and small-angle X-ray scattering. The composite membranes annealed at for 2 h after the fixed drying step showed better ionic conductivity, but no significant increase in thermal stability. The mean Bragg distance between the ionic clusters, which is reflected in the position of the ionomer peak (small-angle scattering maximum), is larger in the annealed composite membranes containing than the non-annealed ones. It might have been explained to be due to the different level of ion-clustering ability of the hydrophilic parts (i.e., sulfonic acid groups) in the non- and annealed polymer matrix. In addition, the ionic conductivity of the membranes shows higher for the annealed composite membranes containing . It can be concluded that the annealing of the composite membranes containing ionic liquids due to an increase in ion-clustering ability is able to bring about the enhancement of ionic conductivity suitable for potential use in proton exchange membrane fuel cells (PEMFCs) at medium temperatures () in the absence of external humidification.

Preparation and Characterization of Nafion Composite Membranes Containing 1-ethyl-3-methylimidazolium Tetracyanoborate

The composite membranes using Nafion as matrix and 1-ethyl-3-methylimidazolium tetracyanoborate (EMITCB) as ion-conducting medium in replacement of water were prepared and characterized. The amount of EMITCB in Nafion varied from 30 to 50wt%. The composite membranes are characterized by ion conductivity, thermogravitational analyses (TGA) and small-angle X-ray scattering (SAXS). The composite membranes containing EMITCB of 40wt% showed the maximum ionic conductivity which was ~0.0146 S cm �1 at 423.15 K. It is inferred that the decrease in ionic conductivity of all the composite membranes might be due to the decomposition of a tetracyanoboric acid formed in the composite membranes. The results of SAXS indicated that the ionic clusters to conduct proton in the composite membranes were successfully formed. In accordance with the results of ionic conductivity as a function of a reciprocal temperature, SAXS showed a proportional decrease in scattering maximum qmax as the amount of EMITCB increases in the composite membranes, which results in the increase in ionomer cluster size. The TGA showed no significant decomposition of the ionic liquid as well as the composite membranes in the range of operating temperature (120-150 o C) of high temperature proton exchange membrane fuel cells (HTPEMFC). As a result, EMITCB is able to play an important role in transferring proton in the composite membranes at elevated tem- peratures with no external humidification for proton exchange membrane fuel cells.

Development of Ionomer Binder Solutions Using Polymer Grinding for Solid Alkaline Fuel Cells

In this study, an anion-exchange ionomer solution was prepared by grinding poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) in liquid nitrogen for solid alkaline fuel cells (SAFCs). Type of quaternized PPO (QPPO) solutions was controlled by grinding time. The ionomer binder solutions were characterized in terms of dispersity, particle size, and electrochemical properties. As a result, ionomer binder solutions using grinded polymer showed higher dispersion and smaller particle size distribution than that using non-grinded polymer. The highest ionic conductivity and IEC of the membrane recast by using BPPO-G120s were and , respectively.