T. I. T. Kudin

Studies on cellulose acetate-based gel polymer electrolytes for proton batteries

Abstract Biomaterial-based cellulose is biodegradable, biocompatible and possesses good mechanical properties. Previous studies have proven that it can be used as the separator for various kinds of batteries, such as lead–acid batteries, silver–zinc rechargeable batteries, as an additive for preparation of pasted zinc electrodes for zinc–air batteries and as binders/surface modifiers for graphite anodes for lithium batteries. However, it never intensively been used as a polymer electrolyte in advanced batteries. Substantial progress has been made in the development of proton conductors with high ionic conductivity. Hence, proton batteries can be considered as cost effective alternatives for battery applications. The present study involves the fabrication and characterisation of gelled cellulose polymer proton battery with the configuration Zn/composite cellulose electrolytes/MnO2. The open circuit voltage (OCV) of the cell is ∼1·6 V. The constancy of OCV was tested for over 24 h. The discharge capacity was 24·65 mA h for 0·5 mA and 22·41 mA h for 1 mA.

First Principles LDA+U Calculations for ZnO Materials

The electronic, structural, elastic, and optical properties of zinc oxide (ZnO) with wurtzite-type structure were investigated using first-principles calculation based on density functional theory (DFT) with local density approximation (LDA) plus Hubbard U (DFT–LDA+U)method. Hubbard U improved the calculated results, allowing it to exhibit good agreement with experimental data. The DFT–LDA+U method successfully predicted the electronic properties of ZnO with better described the localization of transition metal Zn 3d electron. The calculated optical dielectric function of ZnO and its relation with electronic properties were further discussed.

Determination of Electronic Structure and Band Gap of Li2MnP2O7 via First-Principle Study

The pyrochlore Li2MnP2O7 structure is an important new class of cathode for lithium ion batteries. First-principle calculations of ferromagnetic and antiferromagnetic (AFM) Li2MnP2O7 have been conducted within both the local density approximation (LDA) and the LDA+U frameworks. The optimized lattice parameters for AFM configuration calculated using the LDA+U scheme are closest and in good agreement with the experimental results. The electronic density of state analysis shows that Li2MnP2O7 is a charge-transfer insulator with a large band gap (4.183 eV) contributed between the O-2p and Mn-3d states, indicating that Li2MnP2O7 possesses poor electronic conductivity.

Frequency dependent conductivity studies on PMMA–LiCF3SO3 polymer electrolytes

Abstract Polymer electrolytes composed of poly(methylmethacrylate) as a host polymer and lithium triflate as a salt have been prepared by solution cast technique. Polymer salt complexation has been confirmed by attenuated total reflectance Fourier transform infrared spectral studies. The ac conductivity as a function of temperatures in the frequency range 100 Hz–1 MHz has been carried out. The conductivity–temperature plots found follows the Arrhenius rule. The complex permittivity ϵ* and complex electric modulus M* have been analysed. The dispersion observe at low frequency is due to the space charge effect arising from the electrodes. The modulus spectra reveal that the dispersion deviates from the Debye behaviour. The ionic conductivity relaxation is determined from the maximum of the peaks of the dielectric loss modulus associated with the ac activation energy for ion relaxation E fp=0·337 eV, which agrees well with the dc conduction activation energy E A=0·341 eV. Thus, it is suggested that the dynamic mechanism for the ionic conduction is achieved at the same energy barrier while conducting as well as relaxing.

PLASTICIZED PVA/PVP–KOH ALKALINE SOLID POLYMER BLEND ELECTROLYTE FOR ELECTROCHEMICAL CELLS

Solid polymer electrolytes comprising a blend of poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) with different concentration of potassium hydroxide (KOH) as ionic dopant were prepared using a solution–casting technique. The conductivity was enhanced to (1.5 ± 1.1) × 10-4S cm-1 when 40 wt.% KOH was added. The highest conductivity exhibited when 20 wt.% ethylene carbonate (EC) and 30 wt.% propylene carbonate (PC) was added into the PVA/PVP–KOH sample electrolytes. Conductivity–temperature dependence of the plasticized samples was established to obey an Arrhenian relationship with the activation energy of the order of 0.08–0.4 eV, depending on the plasticizer concentration. Electrochemical cells of Zn|PVA/PVP–KOH + EC|MnO2 and Zn|PVA/PVP–KOH + PC|MnO2 have been fabricated. The discharge characteristics of the cells are considered under a constant current of 1 mA. The open circuit voltage (OCV) and discharge capacity of the cells are measured.

Electrochemical performance of activated carbon and graphene based supercapacitor

Abstract A conventional but simple fabrication technique of activated carbon/graphene (AC/G) supercapacitor electrode will be presented in this work. The AC/G electrode was prepared using slurry technique from the mixture of AC and graphene powders, polytetrafluoroethylene as binder and N-methylpyrrolidone as solvent. The AC/G electrode was dried at 120°C in vacuum oven for 6 h followed by immersing in 1M lithium hexafluorophosphate electrolyte for another 6 h. The specific gravimetric capacitance of the electrode was calculated to be 19·45 F g−1 using cyclic voltammetry at a scan rate of 1 mV s−1. Electrochemical behaviour including charge discharge and impedance characteristics confirmed the electrode’s ability as a possible active material for use in carbon based supercapacitor.

First-principles comparative study of the electronic and optical properties of tetragonal (P4mm) ATiO3 (A = Pb,Sn,Ge)

The structural, electronic, and optical properties of the special lone pair ferroelectric materials with tetragonal structures, namely, PbTiO3, SnTiO3, and GeTiO3 (P4mm, 99 space group), were investigated using density functional theory implemented in a pseudo-potential plane wave using the CASTEP computer code. The electronic properties indicated that hybridizations occur among anion O 2p, special lone pair (ns2), and the Ti 3d states. The complex dielectric constant was used to explain the comparison of optical properties of ATiO3 (A = Pb,Sn,Ge) relative to their electron transition from conduction to valence.

Excitation and Emission Properties of Poly(N-Carbazole)/Poly(vinylpyrrolidone) Blends Characterized by Fluorescence Spectroscopy

We present the results concerning the excitation and emissions spectra of Poly (N-carbazole) (PVK) blend with different compositions of polyvinylpyrrolidone (PVP). Doctor blade technique was used to coat the blended polymer on a quartz substrate. The influences of polymer composition to the excitation and emission spectra were observed under UV excitation source of a xenon lamp. The result shows a discrepancy in the maximum excitation, emission and Stokes shift for each samples. The variation of Full Width at Half Maximum (FWHM) for excitation and emission indicate that the variation in composition has affected on the fluorescence properties of the blended thin film polymer system. Fourier Transform Infrared (FTIR) spectroscopy reveals that the discrepancy in the emission and excitation properties of this polymer blending system is due to the discrepancy of infrared absorption peak in the carbazole functional group.

Characterization of poly (N-vinlycarbazole) blending with different composition by using polarized electronic spectroscopy

Polarized absorption and dielectric spectra of blended poly (N-vinlycarbazole) (PVK) with polyvinylpyrrolidone (PVP) in different composition ratiosare investigated. Polymer coating was carried out using doctor blade technique on a quartz substrate. The polarized optical source was produced by using the uv-vis sheet polarizer. The polarized absorption and dielectric spectrum for parallel and perpendicular reveal that there are different significant results obtained between PVK and PVP with various polymer compositions.The polarized optical properties such aspolarization, ρwere calculated.These spectra indicate that the anisotropic properties of each polymer blends is different from each other.

Polarized absorption and dielectric spectra of poly (N-carbazole) blends

Polarized absorption and dielectric spectra of poly (N-carbazole) (PVK) blend with poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) and polyvinylpyrrolidone (PVP) in the same composition ratio were investigated. Polymer coating was carried out using doctor blade technique on a glass substrate. In order to investigate the effect of polarization in polymer blending, we located the uv-vis polarizer before and after the optical excitation source. The polarized absorption and dielectric spectrum for parallel and perpendicular reveal that there are significant different results obtained between PVK, PVK:PVP and PVK:PVDF-HFP. These spectra indicate that the anisotropic properties each polymer blends are different from each other.