Department of Chemical Engineering
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Item Effect of Operating Variables on DMFC Performance for the Synthesized Si-PWA/PVA Nanocomposite Membrane(Life Science Global, 2015) Pandey, JayElectrochemical Performance of DMFC was studied under the effect of various operating parameters like temperature, methanol concentration and relative humidity (RH) for the synthesized silica immobilized phosphotungstic acid-poly(vinyl alcohol) (Si-PWA/PVA) nanocomposite membrane (thickness 80-100 µm). The optimized 1.5 Si-PWA/PVA membrane showed good electrochemical properties (transport number: 0.92 and IEC: 0.90 meq/g) with excellent mechanical strength, thermal and chemical stability. Open circuit voltage (OCV) decay was significantly lower in comparison to Nafion-117. Maximum power density (45.7 mWcm-2) was obtained at 60oC cell temperature. DMFC performance exhibited better performance even at higher methanol concentration (2 M) demonstrating lower concentration over potential. The appreciable rise in the peak power density observed at higher relative humidity (90%) showed good water stability of the membrane. Performance of the DMFC with the synthesized composite membrane was comparable to the state of the art Nafion-117.Item Studies on Black Carbon (BC) Variability Over Northern India(Trade Science Inc, 2013) Pandey, JayIn recent years, the mass concentration of black carbon (BC) aerosol has been increased tremendously resulting into severe fog (winter period) and atmospheric heating thus playing a major role in global warming. So keeping in views all these fatal consequences, the proper measurement of BC mass concentration and its decisive analysis have become very crucial. Therefore the extensive measurement of aerosol BC mass concentration was being carried out by using the instrument Aethalometer at IT-BHU, located in the Indo-Gangetic plane of northern India. So far, the continuous observations for the winter periods have been collected and analyzed thoroughly. The daily average values are significantly high in the early morning hours and at the night hours due to the stable atmospheric boundary layer causing very little dispersion of BC. However, the monthly average values show that the BC mass concentration continuously increasing due to the lowering of temperature and creation of shallow atmosphere. It is expected that for the upcoming months i.e. for winter period the BC mass concentration is going to be higher due the substantial accumulation of BC thus causing severe fog which is completely lashing normal life. Along with this, the meteorological parameters (wind speed, wind direction, % RH, and rainfall status) were also being taken into account since these are the major influencing factors. At present an endeavor was being planned to explore the major contributor of BC in the Varanasi region.Item Graphite Supported Silica Immobilized Phosphotungstic Acid Based Ion-Conducting Inorganic Membrane(ASME, 2018-06) Pandey, JayAn asymmetric, inorganic ion-conducting membrane was synthesized by depositing a top layer containing silica-immobilized phosphotungstic acid (Si-PWA) over a graphite sheet. Surface morphology, thermal stability, and structure of the top layer of the membrane were studied using scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR), respectively. The transport number and specific conductivity of the membrane were measured using membrane potential and impedance measurements, respectively. The composition of the top layer was varied by changing the molar ratio of PWA and tetraethoxy orthosilicate (TEOS) in the casting sol. The transport number and specific conductivity of the membrane increased on increasing PWA fraction in the casting solution. The highest transport number for sodium ion was 0.98 for PWA: TEOS molar ratio of 1.5. Specific conductivity of the membrane, with 0.5 PWA: TEOS, was 0.0082 S cm−1 which was lower compared to the membrane with 1.5 PWA: TEOS of specific conductivity 0.017 S cm−1. The specific conductivity of the membrane increased with increase in the temperature for both 0.5 and 1.5 molar ratio of PWA: TEOS with the calculated activation energy 18.9 and 8.8 kJ/mol, respectively.Item Synthesis and characterization of PWA based inorganic ion-exchange membrane(Elsevier, 2012-09) Pandey, JayPhosphotungstic acid (PWA) based inorganic ion-exchange membrane (IEM) was prepared on graphite support using a simple synthesis protocol. Top layer of the membrane was obtained by immobilizing PWA in silica derived from TetraEthylOrthoSilicate (TEOS) precursor. After casting, the top layer was heat-treated at 150 °C. Membrane surface morphology was observed by using Scanning Electron Microscope (SEM) and the top layer was found to be about 30 μm thick. Fourier transform infrared spectroscopy (FTIR) was used to determine the functional groups and X-ray Diffraction (XRD) was used to study the crystallinity of the top layer. The membrane was found to be thermally stable up to 250 °C obtained from Thermo Gravimetric Analysis (TGA). Static transport number for cation (t+) was determined in the pH range of 2–11 using membrane potential measurements. It was found to be above 0.95 in the pH range of 4–9. Ohmic resistance of the membrane was determined from impedance measurement and it was found to be 12 Ω cm2 which is lower than the reported value for inorganic IEMs and comparable to some of the organic IEMs. Membrane surface was hydrophilic with water contact angle of 9° and this hydrophilic nature might be useful for its use as electrolyte filled separators for batteries and super-capacitors.Item Synthesis and characterization of PVDF supported silica immobilized phosphotungstic acid (Si-PWA/PVDF) ion-exchange membrane, Materials Letters,(Elsevier, 2013-06) Pandey, JayAn ion exchange membrane was synthesized by impregnating sub-micron sized silica-immobilized phosphotungstic acid (Si-PWA) particles on a porous (poly vinylidene fluoride) (PVDF) film. Surface morphology, crystalline nature and thermal stability of the membrane were studied. The membrane was found to have a defect free surface, which contained both crystalline and amorphous phases and was stable up to 350 °C. Electrochemical properties (transport number) of membranes of two different PWA/TEOS (tetraethoxyorthosilicate) ratios were compared and the one with a higher ratio gave better properties. Ion exchange capacity (IEC) of 0.82 meq/g and counter-ion transport number of 0.91 indicated good electrochemical properties of the membrane synthesized with sol of PWA/TEOS ratio of 1.5.Item Zirconium phosphate based proton conducting membrane for DMFC application(Elsevier, 2015-08) Pandey, JayA proton conducting poly(vinylidene fluoride) (PVDF) supported zirconium phosphate (ZrP) ion-exchange membrane (ZrP/PVDF) was synthesized for potential application in DMFC by filling the pores of a PVDF film with in-situ grown ZrP particles. Presence of labile protons attached to Pdouble bondO group was confirmed from 1H NMR and FT-IR characterizations. SEM micrographs showed defect-free top surface. The thermal stability and mechanical strength of the ZrP/PVDF membrane was better than Nafion-117. Water to methanol uptake ratio was higher while methanol cross-over for ZRP/PVDF membrane was lower than Nafion-117. Membrane possessed fair electrochemical properties; 0.85 static counter-ion transport number, 0.76 meqg−1 ion exchange capacity and 1.25 mScm−1 proton conductivity at 30 °C. DMFC performance of the synthesized membrane at 35 °C was compared with the Nafion-117. DMFC studies were also done at different operating conditions and the maximum peak power density was 32.3 mWcm−2 at 60 °C, 1 M methanol concentration and 60% relative humidity.Item PVDF supported silica immobilized phosphotungstic acid membrane for DMFC application(Elsevier, 2014-09) Pandey, JaySilica immobilized phosphotungstic acid (Si-PWA) based inorganic–organic hybrid ion exchange membrane was used in direct methanol fuel cell (DMFC). Chemical composition of the ion exchanging phase of membrane was determined using energy dispersive spectroscopy (EDS). TGA analysis showed that the thermal stability of synthesized membrane was better than Nafion-117 and it also possessed excellent water holding capacity even at elevated temperature. The proton conductivity of the membrane increased upon increasing the PWA concentration in silica. Room temperature (25 °C) proton conductivity of the membrane was 4.3 m Scm− 1 and it increased to 10.1 m Scm− 1 upon increasing temperature to 60 °C. At 25 °C and 60% relative humidity, the peak power density of DMFC with synthesized membrane (21.6 m Wcm− 2) was much better than that of DMFC with Nafion-117 membrane (11 m Wcm− 2).Item Synthesis of silica immobilized phosphotungstic acid (Si-PWA)-poly(vinyl alcohol) (PVA) composite ion-exchange membrane for direct methanol fuel cell(Elsevier, 2014-06) Pandey, JayA 80 μm thick composite ion-exchange membrane was synthesized by uniformly dispersing sub-micron to nano sized silica immobilized phosphotungstic acid (Si-PWA) inorganic ion exchanger into cross-linked poly(vinyl alcohol) (PVA) matrix. ATR-IR spectrum confirmed the PVA cross-linking and presence of Si-PWA in membrane. Amorphous behavior of the membrane indicated uniform blending of crystalline Si-PWA particles with cross-linked PVA. Membrane's tensile strength (93 MPa) was much higher than Nafion 117 (34 MPa). Ion exchange capacity of the membrane (0.90 meqg−1) was higher than the values reported for the other PVA based membranes. Na+ transport number was 0.92, indicating good ion-selectivity of the membrane. Membrane showed a high water uptake of 35% while its methanol uptake was low (8.4%) and thereby reduced methanol permeability (1.6 × 10−7 cm2 s−1) compared to Nafion-117 was observed, a highly desirable property for DMFC application. Proton conductivity increased from 7.04 mS cm−1 to 10.5 mS cm−1 with increase in temperature from 30 °C to 50 °C. At 35 °C, the single cell DMFC with membrane showed higher OCV (0.8 V) and comparable peak power density to Nafion-117.Item Design and synthesis of highly stable poly(tetrafluoroethylene)-zirconium phosphate (PTFE-ZrP) ion-exchange membrane for vanadium redox flow battery (VRFB)(Springer, 2017-01) Pandey, JayVanadium redox flow battery (VRFB) is a promising technology for large-scale renewable energy storage. Design of ion-exchange membrane (IEM) with desired properties like low-cost, mechanically chemically stable, low vanadium ion permeability and high proton conductivity is one of the major challenges. Here, we report the design and synthesis of novel poly(tetrafluoroethylene)-zirconium phosphate (PTFE-ZrP) asymmetric IEM using a simple brush coating method. XRD results confirmed the presence of α-ZrP crystalline phase onto the top layer of the membrane. Excellent mechanical strength was observed with burst pressure of 3.22 × 105 N m−2. Oxidative stability of membrane in Fenton’s reagent was much better than Nafion-115. Vanadium ion (V4+) permeability of the membrane was more than three times lower than that of Nafion-115. Single-cell VRFB with PTFE-ZrP membrane showed ∼80% energy efficiency below 30 mA cm−2. Very high columbic efficiency ∼100% of VRFB with PTFE-ZrP membrane confirmed little contamination of electrolyte due to cross-mixing.Item Performance of the vanadium redox-flow battery (VRB) for Si-PWA/PVA nanocomposite membrane(Springer, 2016-05) Pandey, JayThe performance of Si-PWA/PVA nanocomposite membrane in vanadium redox-flow battery (VRB) is reported. Structurally, the membrane consisted of a dispersion of sub-micron-sized silica immobilized phosphotungstic acid (Si-PWA) inorganic ion-exchanging phase in the continuous phase of cross-linked poly(vinyl alcohol) (PVA). SEM micrographs indicated the defect-free top surface of membrane with similar morphology of Nafion-115. Good ion selectivity and availability of ion-exchangeable sites were observed as indicated by higher transport number (0.89) and ion-exchange capacity (IEC) (1.20 meq g−1), respectively. Oxidative stability of the membrane was good in vanadium ion species (V4+, V3+, and V2+) but its stability in V5+ solution and Fenton’s reagent was slightly lower than Nafion-115. Vanadium ion permeability (0.69 × 10−7 cm min−1) of Si-PWA/PVA membrane was significantly lower than Nafion-115. Suitability for VRB with Si-PWA/PVA membrane was assessed from open-circuit voltage (OCV) decay which was lower compared to Nafion-115. Single-cell VRB with Si-PWA/PVA membrane exhibited lower voltage during charge and higher during discharge with excellent cyclic stability compared to VRB with Nafion-115.