Bhalchandra A. Kakade

Polymer Electrolyte Fuel Cells Using Nafion-Based Composite Membranes with Functionalized Carbon Nanotubes†

Fuel efficiency: Enhanced proton conductivity is obtained by the incorporation of single-walled carbon nanotubes prefunctionalized with sulfonic acid groups (S-SWCNTs) into a Nafion matrix (see scheme). The acid content of the CNT connects the hydrophobic regions of the membrane, thus providing a network for proton mobility. The polymer electrolyte membranes also have improved mechanical stability in H 2 /O 2 fuel cells.

Electric Field Induced, Superhydrophobic to Superhydrophilic Switching in Multiwalled Carbon Nanotube Papers

Superhydrophobic multiwalled carbon nanotube bucky paper, fabricated after ozonolysis, shows fascinating electrowetting behavior, which could be remarkably tuned by changing key solution variables like the ionic strength, the nature of the electrolyte, and the pH of the water droplet. More significantly, the droplet behavior can be reversibly switched between superhydrophobic, Cassie-Baxter state to hydrophilic, Wenzel state by the application of an electric field, especially below a threshold value.

Invertase inhibition based electrochemical sensor for the detection of heavy metal ions in aqueous system: Application of ultra-microelectrode to enhance sucrose biosensor's sensitivity.

We are reporting fabrication and characterization of electrochemical sucrose biosensor using ultra-microelectrode (UME) for the detection of heavy metal ions (Hg(II), Ag(I), Pb(II) and Cd(II)). The working UME, with 25 microm diameter, was modified with invertase (INV, EC: 3.2.1.26) and glucose oxidase (GOD, EC: 1.1.3.4) entrapped in agarose-guar gum. The hydrophilic character of the agarose-guar gum composite matrix was checked by water contact angle measurement. The atomic force microscopy (AFM) images of the membranes showed proper confinement of both the enzymes during co-immobilization. The dynamic range for sucrose biosensor was achieved in the range of 1 x 10(-10) to 1 x 10(-7)M with lower detection limit 1 x 10(-10)M at pH 5.5 with 9 cycles of reuse. The spectrophotometric and electrochemical studies showed linear relationship between concentration of heavy metal ions and degree of inhibition of invertase. The toxicity sequence for invertase using both methods was observed as Hg(2+)>Pb(2+)>Ag(+)>Cd(2+). The dynamic linear range for mercury using electrochemical biosensor was observed in the range of 5 x 10(-10) to 12.5 x 10(-10)M for sucrose. The lower detection limit for the fabricated biosensor was found to be 5 x 10(-10)M. The reliability of the electrochemical biosensor was conformed by testing the spike samples and the results were comparable with the conventional photometric DNSA method.

Photoluminescence studies of Eu3+ doped Y2O3 nanophosphor prepared by microwave hydrothermal method

In this letter, the authors report the photoluminescence studies of Eu3+ doped Y2O3 nanorods, which have been synthesized by rapid microwave hydrothermal route within 6min. The nanostructured Eu3+ doped Y2O3 is characterized by x-ray diffraction, transmission electron microscopy, and photoluminescence. The emission spectrum shows transitions from the excited 5D0 state to FJ7 (J=0,1,2,3,4) levels of the Eu3+ ion. The most intense peak around 612nm is due to the D05→F27 transition, expected from the Judd-Ofelt selection rules [B. R. Judd, Phys. Rev. 127, 750 (1962); G. S. Ofelt, J. Chem. Phys. 37, 511 (1962)]. Photoluminescence measurements demonstrated that the nanocrystalline Eu3+:Y2O3 phase shows higher photoluminescence intensity.

Enhanced activity and durability for the electroreduction of oxygen at a chemically ordered intermetallic PtFeCo catalyst

We have designed a chemically ordered face-centred tetragonal intermetallic PtFeCo (trimetallic) (fct-TM) alloy catalyst using a simple solid-state impregnation method for the oxygen–reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). The fct-TM catalyst has demonstrated both enhanced activity and durability, unlike many Pt alloys. The chemical ordering of the fct-TM was verified by high-angle annular dark-field scanning transmission electron microscopy. The ORR activity of fct-TM was examined using the rotating-disk electrode (RDE) technique and the results are compared with those for a chemically disordered face-centred cubic (fcc), fcc-TM catalyst, and a commercial catalyst from Tanaka Kikinzoku Kogyo, TKK-PtC. The fct-TM displayed superior catalytic (mass) activity relative to disordered fcc-TM and TKK-PtC. The mass activity of fct-TM (0.505 A mgPt−1) is 2.5 times higher than that of TKK-PtC (0.23 A mgPt−1). The durability of these catalysts was evaluated over 5000 (5k) potential cycles in the lifetime regime. The fct-TM retained 80% of its initial mass activity and electrochemically active surface area (ECSA); however, fcc-TM and TKK-PtC maintained about 50% and 70% activity, respectively. The fct-TM also retained the chemically ordered structure after 5k durability cycles. This was confirmed using selected-area electron-diffraction (SAED) patterns. Furthermore, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scans of the fct-TM catalysts after 5k durability cycles revealed that Fe and Co were found similar to as before cycling, which signifies that the dissolution of Fe and Co was impeded by the fct-TM catalysts. The observed enhancement in durability might be due to the ordered arrangement of Pt and Fe/Co within the alloy.

High current density, low threshold field emission from functionalized carbon nanotube bucky paper

Field emission studies of bucky paper of multiwalled carbon nanotubes (MWNTs), prepared after microwave (MW) assisted acid functionalization are reported along with a comparison with that of “as-grown” sample. MW treated bucky papers reveal an interesting linear field emission behavior in Fowler–Nordheim plot. The field emission currents at preset value are found to be remarkably stable over a period of more than 3 h sustaining current densities of 4.9 mA/cm2 and 8.5 mA/cm2 for “as-grown” and functionalized sample, respectively. The enhancement in the field emission due to functionalization has been discussed in terms of tip opening and defect induced charge transport caused by intershell and intertubular interaction.

Enhanced oxygen reduction reaction by bimetallic CoPt and PdPt nanocrystals

Excellent oxygen reduction reaction (ORR) activity of Pt-based bimetallic alloys like CoPt and PdPt has been studied in detail. A simple solution-phase synthetic procedure for the bimetallic alloys of CoPt and PdPt is described here. This method, involving a single-step reaction, is believed to be suitable for large-scale synthesis of both monometallic and multimetallic nanocrystals with required size and shape. Among various catalyst compositions, Pd22Pt78 and Co15Pt85 catalysts have shown excellent ORR activity compared with Pt/C and commercial PtCo/C (PtCo/C(comm)) samples. At 0.9 V, Co15Pt85/C and Pd22Pt78/C exhibit mass activities with values ∼3.8 times and ∼2.1 times higher than that of Pt/C, and Co15Pt85/C exhibits 1.8 times higher activity than that of PtCo/C(comm). Quantification and the effect of surface-oxygenated species generated at higher potentials were studied by stripping voltammetry, in the form of total charge.

Three dimensional nanocomposite of reduced graphene oxide and hexagonal boron nitride as an efficient metal-free catalyst for oxygen electroreduction

The present work demonstrates a simple and inexpensive method for the synthesis of a reduced graphene oxide/boron nitride (rGO/BN) nanocomposite using a one step hydrothermal method followed by annealing at high temperature. The structural analysis confirms the formation of a homogeneous composite with coalescence of the graphitic layers of reduced graphene oxide and hexagonal boron nitride (h-BN), making an ideal situation for better oxygen adsorption followed by electroreduction. The morphology study also clearly indicates a uniform distribution of boron nitride particles at both sides of the stratified graphene oxide. Interestingly, the electrochemical study implies that the rGO/BN nanocomposite shows a substantially higher oxygen reduction reaction (ORR) activity with a single step nearly 4-electron transfer pathway and an improved onset potential of ∼0.8 V versus RHE in alkaline conditions. Though the onset potential is inferior to Pt based catalysts, it is much superior to previously reported carbon or h-BN based electrocatalysts. However, the present rGO/BN nanocomposite catalysts show higher stability than commercial Pt/C catalysts even after 10 000 cycles, and hence it could be a first report of ORR by metal-free h-BN based materials. Additionally, this composite catalyst does not have any methanol oxidation reactions that nullify the issues due to the fuel cross-over effect in direct methanol fuel cells.

Carbon nanotube-modified sodium dodecyl sulfate-polyacrylamide gel electrophoresis for molecular weight determination of proteins.

The effect of incorporating carbon nanotubes (CNTs) in the gel matrix on the electrophoretic mobility of proteins based on their molecular weight differences was investigated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). More specifically, a reduction in standard deviation in the molecular weight calibration plots by 55% in the case of multiwalled carbon nanotubes (MWCNTs) and by 34% in the case of single-walled carbon nanotubes (SWCNTs) compared with that of pristine polyacrylamide gels was achieved after incorporating an insignificant amount of functionalized CNTs into the gel matrix. A mechanism based on a more uniform pore size distribution in CNT modified polyacrylamide gel matrix is proposed. Furthermore, the impact of SWCNTs and MWCNTs on the mobility of proteins in different molecular weight regimes at a given acrylamide concentration offers a tunable gel matrix in terms of the selection of molecular weight ranges of proteins. The robustness and excellent reproducibility of the CNT-PAGE protocol are expected to have a significant impact on the molecular weight determination of newly isolated proteins.

Enhanced methanol electrooxidation at Pt skin@PdPt nanocrystals

Pt skin growth over PdPt alloy nanocrystals has been described using a simple wet chemical method, where a layer-by-layer epitaxial deposition of Pt on PdPt could be understood by the Stranski–Krastanov mechanism. Initial PdPt alloy nanocrystals grown in a simple wet-chemical method, in the presence of a reducing solvent like N-methyl pyrrolidone (NMP) and a stabilizer like polyvinyl pyrrolidone (PVP), have been used as the substrate for secondary growth of a Pt thin layer. Surface changes have been observed during step-by-step growth of polyhedral Pt skin@PdPt nanocrystals originating from nearly octahedral geometries of PdPt. The methanol electrooxidation activities of two different Pt skin@PdPt nanostructures have been compared with PdPt nanocrystals with similar compositions but without skin structures and commercial RuPt catalysts. A gain factor of 8 towards electrooxidation of methanol in acidic media with activities of 1950 mA mgPt−1 and 3.1 mA cmPt−2 (with lower onset potential compared to the RuPt commercial catalyst), which is believed to be much higher compared to that of previous reports and state-of-art RuPt/C catalysts, indicating better surface properties and core-alloy formation along with improved intraparticle active interfacial sites. Additionally, exciting results of electrooxidation of ethanol and ethylene glycol with 70% and 58% activity retention respectively, after 5000 cycles are also found, demonstrating a facile C–C breaking in such C2 type alcohols.