Dipali Banerjee

Reduced graphene oxide-polyaniline composites—synthesis, characterization and optimization for thermoelectric applications

Reduced graphene oxide (rGO) can improve the thermoelectric properties of polyaniline (PANI) by varying its concentration in composites of rGO nanosheets and PANI. The figure of merit (ZT) of rGO–PANI composites is increased with an increasing percentage of rGO (up to 50%), which is 7.5 times higher as compared to pure PANI. High resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analyses show a uniform growth of PANI over the surface of rGO as a template, leading to a more ordered structure with high crystallinity during polymerization. Compared to pure PANI, both the electrical conductivity and thermoelectric power of the rGO–PANI composite is higher due to the increased carrier mobility as confirmed by a Hall effect measurement. Fourier transform infrared spectroscopy (FTIR), ultra-violet visible range spectroscopy (UV-Vis) and Raman spectroscopy analyses reveal that strong π–π interactions assisted the uniform distribution of PANI on the rGO nanosheets. Other strong interactions include electrostatic forces and hydrogen bonding between rGO and PANI, which provide a route for constructing highly ordered chain structures with improved thermoelectric performance of PANI. There is no significant change in the thermal conductivity of the rGO–PANI composite as compared to pure PANI, which improves the thermoelectric performance of composite.

Synthesis, characterization and enhanced thermoelectric performance of structurally ordered cable-like novel polyaniline–bismuth telluride nanocomposite

Bismuth telluride (Bi₂Te₃) nanorods and polyaniline (PANI) nanoparticles have been synthesized by employing solvothermal and chemical oxidative processes, respectively. Nanocomposites, comprising structurally ordered PANI preferentially grown along the surface of a Bi₂Te₃ nanorods template, are synthesized using in situ polymerization. X-ray powder diffraction, UV-vis and Raman spectral analysis confirm the highly ordered chain structure of PANI on Bi₂Te₃ nanorods, leading to a higher extent of doping, higher chain mobility and enhancement of the thermoelectric performance. Above 380 K, the PANI-Bi₂Te₃ nanocomposite with a core-shell/cable-like structure exhibits a higher thermoelectric power factor than either pure PANI or Bi₂Te₃. At room temperature the thermal conductivity of the composite is lower than that of its pure constituents, due to selective phonon scattering by the nanointerfaces designed in the PANI-Bi₂Te₃ nanocable structures. The figure of merit of the nanocomposite at room temperature is comparable to the values reported in the literature for bulk polymer-based composite thermoelectric materials.

Facile electrochemical deposition of Cu7Te4 thin films with visible-light driven photocatalytic activity and thermoelectric performance

We report a facile strategy to fabricate thin films of Cu7Te4 via a two-electrode galvanic method and demonstrate its application as a recyclable photocatalyst with visible-light-driven photocatalytic activity and photostability. The organic dyes Methylene Blue (MB), and Rose Bengal (RB) and Cr(VI) as a toxic metal ion were chosen to explore the photocatalytic performance. MB was completely degraded (97%) under visible light irradiation in 60 min while RB was degraded up to 92% within 90 min irradiation. Furthermore, the Cu7Te4 thin film also showed superior photoactivity to reduce toxic Cr(VI) to Cr(III). The effective removal of Cr(VI) up to 99.8% at pH 2 was observed in 30 min. The related photocatalytic mechanism is discussed based on the active species trapping experiments. In addition, the Cu7Te4 thin film shows improved thermoelectric performance at room temperature, which may be attributed to the lower value of thermal conductivity obtained in the present case.

Analysis of Drying and Dilution in Phosphoric Acid Fuel Cell (PAFC) Using Galvanometric Study and Electrochemical Impedance Spectroscopy

Different experimental and analytical techniques namely steady state galvanometric study and electrochemical impedance spectroscopy (EIS) are employed to generate rule sets for identification of the acid drying and dilution phenomena in a phosphoric acid fuel cell (PAFC). The slope of steady state current versus voltage is used as a performance marker. A new parameter D, which signifies the net moisture transport in PAFC, is introduced and evaluated from the experimental data to locate the regimes of electrolyte dilution and drying. Based on these two parameters, the performance of a PAFC is mapped on the plane of operating variables. Performance decay at higher cell temperature and lower humidifier temperature (below 60 � C) signifies acid drying; on the contrary the same at lower cell temperature and higher humidifier temperature is attributed to acid dilution. EIS is employed by imposing a sinusoidal potential excitation on steady state DC load and the shift of maximum phase angle position in the frequency spectrum is used as a diagnostic marker. Results show absence of peak in the domain of positive frequency for acid drying condition, while acid dilution causes the peak to be shifted at higher frequency value. Electrochemical timescales estimated from EIS increases by many order of magnitudes compared to that in a normal PAFC, when electrolyte drying occurs. The results obtained from EIS analysis are in agreement with the performance mapping based on galvanometric steady analysis. The results are significant in context of water management and humidity control in a PAFC. The tools and parameters introduced in the present publication show promising potential to map the performance and SOH of a PAFC on the plane of various operating variables. Results and logics revealed are of significance in development of inferential model for the online optimization of PAFC. [DOI: 10.1115/1.4026622]

Performance enhancement of phosphoric acid fuel cell by using phosphosilicate gel based electrolyte

Abstract Replacement of phosphoric acid electrolyte by phosphosilicate gel based electrolytes is proposed to enhance the performance of phosphoric acid fuel cell (PAFC). Phosphosilicate gels in paste form and in powder form are synthesized from tetraethoxysilane and orthophosphoric acid by using sol-gel method, for two different P/Si ratios of 5 and 1.5, respectively. Replacement of phosphoric acid electrolyte by phosphosilicate gel paste enhances the peak power generation of the fuel cell by 133% at a cell temperature of 120°C, increases the voltage generation in the ohmic regime and extends the maximum possible load current. Polyvinyl alcohol (PVA) is used to bind the phosphosilicate gel powder and to form the hybrid crosslinked gel-polymer electrolyte membrane. Soaking the membrane with phosphoric acid solution instead of with water improves the proton conductivity of the membrane, enhances the fuel cell voltage and power generation and extends the maximum possible operating temperature. At a low temperature of 70°C, peak power produced by phosphosilicate gel polymer electrolyte membrane fuel cell (PGMFC) is increased by 40% compared to that generated by phosphoric acid fuel cell (PAFC). However, the performance of composite membrane diminishes as the cell temperature increases. Thus the phosphosilicate gel in paste form is found to be a good alternative of phosphoric acid electrolyte at medium operating temperatures, while the phosphosilicate gel PVA composite performs better at low operating temperatures.

Composite of single walled carbon nanotube and sulfosalicylic acid doped polyaniline: a thermoelectric material

Nanocomposites containing single walled carbon nanotubes (SWCNTs) and highly ordered polyaniline (PANI) have been synthesized employing an in situ polymerization using different weight percentages of single-walled carbon nanotube (SWCNT) as template and aniline as a reactant. The composites show homogeneously dispersed SWCNTs which are uniformly coated with PANI through a strong interface interaction. Structural characterization shows that the PANI cultivated along the surface of the SWCNTs in an ordered manner during the SWCNT-directed polymerization process. Measurements at room temperature displayed a significant enhancement in both the electrical conductivity and thermoelectric power which could be attributed to the more ordered chain structures of the PANI on SWCNT. As a result, the power factor of the composite is improved which increases with temperature. At the same time, the measured value of thermal conductivity at room temperature being lowest among the reported values, has resulted in best ZT at room temperature. The lowest value of thermal conductivity is attributed to the large phonon scattering due to the introduction of nanointerfaces.

Effect of different surfactants and thicknesses on electrodeposited films of bismuth telluride and its thermoelectric performance

Thin films of bismuth telluride using various surfactants such as sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP) have been electrochemically deposited. The influence of different surfactants on crystal orientation and morphology was investigated and correlated with the thermoelectric performance of the electrodeposited films. Since thickness affects the thermoelectric performance compared to the surfactant, thickness- dependent thermoelectric performance has also been investigated. The carrier mobilities of the films obtained are significantly enhanced due to improved surface morphology using different surfactants. Between the two surfactants, films with SDS exhibited the higher value of thermoelectric power, power factor, and figure of merit, which is due to the effect of micelle formation. The XRD pattern of all the films, which are electrodeposited without surfactant or using SDS and PVP, showed preferred crystal orientation along the (018) direction. The roles of organic molecules in the development of nanoparticles with improved thermoelectric properties have been investigated.

Change of sign of hall coefficient with variation of magnetic field in acceptor doped Bi

Abstract Change of sign of the Hall effect with magnetic field has been observed in doped Bi. A model for explaining this phenomenon has been proposed which can also explain some other related observations made by the present authors or by others working in the field. This model utilizes the process of excitation of carriers above the Fermi surface when the Fermi energy is small.

Polyaniline–single walled carbon nanotube composite – a photocatalyst to degrade rose bengal and methyl orange dyes under visible-light illumination

The polyaniline/single walled carbon nanotube (PANI–SWCNT) composites were prepared by the polymerization of an aniline monomer in the presence of sulfosalicylic acid with SWCNT under in situ conditions. PANI and PANI–SWCNT composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultra violet-visible spectroscopy (UV-Vis), Fourier transform infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and Brunauer–Emmett–Teller (BET) analysis. The application of the composites as a recyclable photocatalysts with visible-light-driven photocatalytic activity and photostability for the degradation of organic dyes – Rose Bengal (RB) and Methyl Orange (MO) – is demonstrated. PANI–SWCNT composite, with 2 weight% SWCNT content, has emerged as the best with degradation efficiencies of 95.91% and 90.34% against the performance of PANI with degradation efficiencies of 85.2% and 75.9% for RB and MO within 10 and 30 minutes, respectively. The synergistic effect between PANI and SWCNT is found to impart improved photogenerated carrier separation in the composite. A possible photocatalytic mechanism on the enhancement of the visible light performance of the composite over pure PANI is discussed based on the results of an active species trapping experiment.

Conductivity of phosphoric acid: an in situ comparative study of proton in phosphoric acid fuel cell

Phosphoric acid fuel cell (PAFC) unit has been constructed to obtain the concentration-dependent proton conductivity at of aqueous phosphoric acid at different cell temperatures and fixed humidifier temperature. The proton conductivity of the acid has also been measured at different temperatures using an electrolysis cell. The experimental results obtained from different cells have been compared with the conductivity obtained from the theoretical simulation. The simulated proton conductivity values at different cell temperatures matched very well with that obtained from electrolysis cell. However, the proton conductivities obtained from PAFC unit are found to be three orders less than those of the simulated values which may be due to transport limitations. Geometry optimization and potential energy surface scans using ab initio calculations indicate that the proton transfer in the cell can be enhanced by the dilution of the phosphoric acid which significantly improves the generation of hydrogen bonds.