Lal Bahadur

Synthesis, structure and light-harvesting properties of some new transition-metal dithiocarbamates involving ferrocene.

Nine new transition-metal dithiocarbamates involving ferrocene (Fc), namely, [M(FcCH(2)Bzdtc)(2)] (M=Ni(II) (1), Cu(II) (2), Cd(II) (3), Hg(II) (4), Pd(II) (5), Pt(II) (6) and Pb(II) (7); Bzdtc=N-benzyl dithiocarbamate) and [M(FcCH(2)Bzdtc)(3)] (M=Co(II) (8) and UO(2) (VI) (9)), have been synthesised and characterised by micro analyses, IR spectroscopy, (1)H and (13)C NMR spectroscopy, and in three cases by single-crystal X-ray analysis. The peak broadening in the (1)H spectrum of the copper complex indicates the paramagnetic behaviour of this compound. A square-planar geometry around the nickel and copper complexes and distorted linear geometry around the mercury complex have been found. The latter geometry is attributed to the bulkiness of the methylferrocenyl and benzyl groups. The observed single quasi-reversible cyclic voltammograms for complexes 2, 8 and 9 indicate the stabilisation of a metal centre other than Fe in their characteristic oxidation state. These complexes have been used as a photosensitiser in dye-sensitised solar cells.

Studies on semiconducting thin films prepared by the spray pyrolysis technique for photoelectrochemical solar cell applications: Preparation and properties of ZnO

Abstract Thin films of ZnO on glass substrate have been prepared by the spray pyrolysis method using aqueous solution of Zn(NO 3 ) 2 ·4 H 2 O. Conditions of the preparation have been optimized to get good quality films with required properties. The films have been characterized for their structural, optical and electrical properties. X-ray diffraction analysis showed that the deposited material was pure zinc oxide with hexagonal wurtzite-type structure. Optical absorption spectra show high transparency of the film ( ≈ 90–95% transmission) in the visible range with a sharp absorption edge around 380 nm wavelength of light which closely corresponds to the intrinsic band-gap of ZnO (3.2 eV). The conductivity of the deposited film could be increased by approximately five orders of magnitude by annealing it in hydrogen at 400°C. In this way a film with conductivity ≈ 10 ω −1 cm −1 could be obtained. The adherence of the film on glass substrate was quite good.

Photoelectrochemical Studies on Dye‐Sensitized Particulate ZnO Thin‐Film Photoelectrodes in Nonaqueous Media

For dye-sensitized solar cells, it is advantageous to use semiconductor electrodes in the form of thin particulate films (prepared from nanometer-sized colloidal particles) owing to their large surface area. The present report shows that nanocrystalline particulate ZnO thin film electrodes sensitized by rhodamine B give excellent photoresponse in nonaqueous media under visible light illumination. Even by monochromatic light (λ = 550 nm) of low intensity (300 μW/cm 2 ), high open-circuit photopotentials up to 280 mV were generated using these electrodes. Under short-circuit conditions, the maximum incident photons to current conversion efficiency was found to be 8.5% at the peak wavelength of 555 nm in acetonitrile medium. The electrodes were found to be fairly stable in nonaqueous solvents and gave considerably high conversion efficiencies and fill factors. These relatively high efficiencies are indicative of low recombination losses in nanocrystalline particulate film electrodes.

Application of π-Extended Ferrocene with Varied Anchoring Groups as Photosensitizers in TiO2-Based Dye-Sensitized Solar Cells (DSSCs)

Two new compounds, FcCH=NC(6)H(4)COOH (1) and FcCH=NCH(2)CH(2)OH (2) (Fc=C(5)H(4)FeC(5)H(5)), have been synthesized and characterized by elemental analyses, IR and (1)H NMR spectroscopy, and ESI-MS. Attempt has been made to explain their quasi-reversible redox behavior evidenced by cyclic voltammetry using density functional theory (DFT) calculations. Light-harvesting properties of both the compounds and also the starting material, FcCHO (3), have been studied using these compounds as photosensitizers in TiO(2)-based dye-sensitized solar cells having either a propylene carbonate-based electrolyte or ionic liquid electrolyte, namely, 1-propyl-3-methyl imidazolium iodide (PMII). Long-term stability of the photocurrent output of the cell using compound 1 as photosensitizer has been monitored periodically over 1400 h.

Conductance studies in amide-water mixtures. II. Sodium salts inN,N-dimethylformamide-water mixtures at 35C

Conductance data for sodium nitrite, chloride, and acetate in water andN,N-dimethylformamide (DMF)-water mixtures (74.82≥D≥42.48) for the concentration range 0.001–0.04N, as well as the densities, viscosities, and dielectric constants of the solvent mixtures at 35°C, are reported. The data have been analyzed by the Fuoss (1975) equation. The existence of a maximum in the viscosity at a 1∶3 mole ratio of DMF and water is indicated. The Walden products for all the three salts pass through a maximum while the equivalent conductances show a minimum with increasing DMF content. The maxima in the Walden product are attributed to the dehydration of ions by the cosolvent (DMF).

Preparation and characterization of thin films of LaNiO3 for anode application in alkaline water electrolysis

LaNiO3 electrodes were prepared, in the form of thin films on platinum by the methods of spray pyrolysis and sequential coating of mixed metal nitrate solutions followed by thermal decomposition. The films were adherent and of p-type semiconducting. Cyclic voltammetric studies indicated the formation of a quasireversible surface redox couple, Ni(iii)/Ni(ii), on these films before the onset of oxygen evolution in 1 m KOH. The anodic Tafel slopes were ∼40 and ∼65 mV decade−1, on the sprayed LaNiO3 film and on the film obtained by a layer method, respectively. The reaction order with respect to OH− was found to be 2.2 on the sprayed oxide film and 1.2 on the layer film. The sprayed oxide film was found to be electrocatalytically more active. It is suggested that the oxygen evolution reaction proceeds on both the film electrodes via the formation of the physisorbed H2O2 as an intermediate in the rate determining step.

Natural Pigments from Plants Used as Sensitizers for TiO2 Based Dye-Sensitized Solar Cells

Four natural pigments, extracted from the leaves of teak (Tectona grandis), tamarind (Tamarindus indica), eucalyptus (Eucalyptus globulus), and the flower of crimson bottle brush (Callistemon citrinus), were used as sensitizers for TiO2 based dye-sensitized solar cells (DSSCs). The dyes have shown absorption in broad range of the visible region (400–700 nm) of the solar spectrum and appreciable adsorption onto the semiconductor (TiO2) surface. The DSSCs made using the extracted dyes have shown that the open circuit voltages () varied from 0.430 to 0.610 V and the short circuit photocurrent densities () ranged from 0.11 to 0.29 mA cm−2. The incident photon-to-current conversion efficiencies (IPCE) varied from 12–37%. Among the four dyes studied, the extract obtained from teak has shown the best photosensitization effects in terms of the cell output.

Photoelectrochemical investigations on particulate ZnO thin film electrodes in non-aqueous solvents

Abstract This particulate films of ZnO prepared from its ultrafine colloidal particles obtained by the sol-gel technique were studied as photoelectrodes in non-aqueous photoelectrochemical cells. With the use of non-aqueous (acetonitrile and propylene carbonate) electrolytes, higher photovoltage and photocurrent were observed as compared with those obtained with aqueous electrolyte. In propylene carbonate medium the particulate ZnO thin film electrode exhibited an almost ideal current-potential characteristic. By measuring the open-circuit photovoltage ( V oc ) and short-circuit photocurrent ( i sc ) as a function of monochromatic light ( λ = 360 nm) intensity, the diode quality factor ( n ) and reverse saturation current ( i o ) were evaluated as n = 1.5 and i o = 0.75 nA in propylene carbonate medium and i o = 2.6 nA in acetonitrile electrolyte. The Mott-Schottky plots for particulate ZnO thin film electrodes were found to be non-linear, so the flat-band potentials in various solvents were determined using the approximated Gartner equation (i.e. from the i photo 2 vs. V curve). Transient photocurrent-time profiles were also determined in various solvents using white light as well as monochromatic light for irradiation of the working electrode. The incident photon-to-current conversion efficiency (IPCE) at the peak wavelength ( λ = 360 nm) was found to be 27%, 24% and 14% in propylene carbonate, acetonitrile and aqueous electrolytes respectively, indicating clearly the advantage of non-aqueous solvents. The power conversion efficiency of the cell was found to vary with a change in counterelectrode and electrolyte medim. A high power conversion efficiency of about 1.8% was found in the case of propylene carbonate medium and carbon counterelectrode for monochromatic incident light ( λ = 360 nm). The fill factor in this case was 0.49.

Photoelectrochemical studies of cobalt-doped ZnO sprayed thin film semiconductor electrodes in acetonitrile medium

Photoelectrochemical properties of polycrystalline ZnO thin film electrodes doped with cobalt have been studied with particular emphasis on the extension of the photoresponse to the visible region. The film composition was found to differ from the composition of the spray solution. Films with a conductivity as high as 34 S cm− were obtained. The photocurrent-potential curves, absorption and action spectra of Co-doped ZnO electrodes indicated the significant extension to the visible region of its spectral response, confirming thereby the presence of Co2+ in tetrahedral sites of the ZnO lattice.

Electrochemical behaviour of brass (Cu/Zn, 63/37) in binary mixtures of acetonitrile and water

Electrochemical behaviour of commercial brass, 63/37 (Cu/Zn) in acetonitrile (AN) and water mixtures of varying compositions (ie 2–100 m/o AN) at 30°C has been studied using accelerated weight loss method, solution analysis and potentiostatic polarization technique. It is found that during anodic polarization brass exhibits an active-passive transition in 2, 5, 10, 2o and 30 m/o AN, while no passivity has been observed in 50, 70, 95 and 100 m/o AN. Further the dissolution of brass has been found to be cathodically controlled. The open-circuit potential measurements show that as AN content in the solvent mixture increases, both immersion as well as steady potentials gradually shift towards less noble direction. The weight loss and solution analysis show preferential dissolution of zinc in the initial stages which progressively decreases with time.