• Volume 10, Issue 4

      July 1988,   pages  267-400

    • Foreword

      C N R Rao S H Pawar

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    • Prospects for chemical trapping for solar energy

      Balu Venkataraman

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    • Photoelectrochemical devices—a multipurpose system

      A Sinha

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      Various types of photoelectrochemical devices for solar energy convesion are reviewed and the future areas of research delineated.

    • Recent trends in photoelectrochemical cells

      G V Subba Rao

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      A brief survey is presented of the recent developments and emerging trends in research in photoelectrochemical cell for solar energy conversion utilizing semiconductor electrodes.

    • Bulk versus surface state contributions to the efficiency of perovskite titanate photoanodes

      L Gomathi Devi T R N Kutty M Avudaithai

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      Attempts have been made to enhance the photon efficiency of perovskite titanate electrodes during band gap illumination by increasing the bulk dielectric constant with the substitution of suitable isovalent ions in the lattice so that the Curie point is shifted to room temperature and by decreasing theND values with controlled chemical reduction. The photoresponse showed only marginal improvements with these changes in the bulk characteristics. In comparison, the efficiency increased considerably when the electrode surfaces are treated by exposing to dilute acids, particularly HNO3 + HF, for extended periods of time. This is accompanied by the changes inVon to cathodic direction, red shift in the spectral dependence of photoresponse and marginal decrease ofND in the space charge layer. X-ray photoelectron spectra show that the treated electrode surfaces are not uniform with respect to oxygen/titanium ratios, hydroxyls and fluoride incorporated. The enhanced photon efficiency arises from the combined effect of eliminating the undesirable electron recombination centres in the space charge layer and the presence of heterogeneous surface regions leading to non-uniform potential distribution near the electrode surface. The results also point to the limitations of applying Schottky barrier model for semiconductor/electrolyte interface with higher concentrations of surface states.

    • Transient photocurrent response of p-Si/0·5 M H2SO4 interface

      K G Anuradha A Q Contractor

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      An experimental study of the transient photocurrent response of p-Si/0·5 M H2SO4 interface is presented. The results have been analysed in terms of a theoretical model wherein surface states are assumed to be present at a discrete levelEs and communicate exclusively with the semiconductor. The results indicate substantial Fermi level pinning at this interface. Influence of surface oxide films and Pt deposition on the transient response is also discussed.

    • Photoelectrochemical properties of metal-cluster oxide compounds, A2Mo3O8 and (LiY)Mo3O8

      M Paranthaman G Aravamudan G V Subba Rao

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      PEC studies on the single crystals of the metal-cluster oxide compounds. A2Mo3O8 (A = Zn, Mg, Fe), and polycrystalline LiYMo3O8 are reported. The photoresponse behaviour is attributed to the Mod-d transition. The photopotential, the photocurrent vs applied voltage and the wavelength data indicate thatn-Zn2Mo3O8 is stable and possesses a small and indirect band gap of 1·55 eV and a direct band gap of 1·9 eV. With change in A ions in A2Mo3O8, there is no significant change in the PEC properties. LiYMo3O8 is found to be ofp-type. PEC studies show that excepting for poor electronic conductivity, A2Mo3O8 possesses all the requisitie characteristics of an ideal photoanode for PAE of water for trapping solar energy.

    • Photoelectrochemical solar cells using electrodeposited GaAs and AlSb semiconductor films

      S Chandra N Khare H M Upadhyaya

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      Electrodeposited GaAs and AlSb thin film semiconductors were prepared under various deposition conditions. Reasonable stoichiometry could be attained as revealed by EDAX studies. The best stoichiometry was obtained are Ga1·04As0·96 and Al1·12Sb0·88. The band gap of the GaAs and AlSb films was ∼1·5 eV and 1·6 eV respectively. The electrochemical and photoelectrochemical studies on these films are reported with different redox-couples in aqueous and non-aqueous medium.

    • Photoelectrochemical conversion using sprayed CdSe

      J P Mangalhara R Thangaraj O P Agnihotri

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      CdSe films on titanium have been prepared by spray pyrolysis and characterized by X-ray diffraction and X-ray photon spectroscopy. Photoelectrochemical solar cells with 4·84% conversion efficiency have been fabricated using these electrodes. Spectral response studies indicate absorption at sub-band gap energies. The band gap of CdSe as determined from photo-current studies was 1·66 eV. The flat band potential measured gives a value of −1·54 V with reference to SCE for electrodes prepared using cadmium chloride and selenourea in the 1:1 ratio.

    • Studies on K-Sb-S films deposited at different substrate temperatures and their photoelectrochemical behaviour

      C H Bhosale C D Lokhande S H Pawar

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      The electrical and optical properties of thin films of K-Sb-S prepared by spraying a solution of antimony potassium tartrate and thiourea onto heated conducting and non-conducting glass substrates are described. The polycrystalline films produced at an optimum spray rate and at different substrate temperatures were characterized for semiquantitative analysis. The films show variation in thickness with substrate temperature. Photoelectrochemical cells formed with the K-Sb-S film electrode, 0·5 M ferrocene in dimethylsulphoxide as the electrolyte and carbon as the counterelectrode were studied for their current voltage characteristics in dark and in light. Variation of short circuit current and open circuit voltage with light excitation intensity is also described.

    • CdTe photoelectrochemical solar cells—chemical modification of surfaces

      K C Mandal S Basu D N Bose

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      Chemical modification of bothn andp type CdTe has been found to improve the performance and stability of PEC solar cells. The surfaces, modified by Ru3+, have been examined by a variety of techniques. Modification results in enhanced barrier height at the surface due to the formation of a passivating oxide layer.

    • Electrosynthesis and photoelectroactivity of polycrystallinep-zinc selenide

      Kehar Singh J P Rai

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      The photoelectroactivity of polycrystalline zinc selenide films prepared by electrochemical codeposition in zinc sulphate solutions of different concentrations containing theI/I2 redox couple has been investigated. Measured photopotentials, photocurrents and the initial rate of build-up of photopotentials indicate a significant enhancement in photoelectro-convertibility with increase in concentration, in spite of practically no change in the flat band potentials. The photoelectroactivity of ap-n heterojunction photoelectrochemical cell using cadmium selenide along with zinc selenide has also been studied.

    • Electrosynthesis of conducting polyanilines in biphasic media

      P A K Nedungadi Sunita Baweja K Zutshi

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      The electrochemical polymerization of aniline has been studied in the biphasic media. One phase comprises a polar medium containing some added electrolytes and the other a non-polar solvent containing the monomer. Ferric chloride has been used as the supporting electrolyte to catalyse the process of electropolymerization. Polyaniline was obtained in moderate yields with the highestRp of 0·0237% per hour and a maximum polymerization efficiency of 61·65 ¢ 10−2 mol/Faraday. The observations and experimental results suggest a cationic mechanism.

    • Studies on iron-chromium redox storage system

      S H Pawar R D Madhale P S Patil C D Lokhande

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      The performance of the redox storage battery based on the Fe-Cr redox couple is studied in charging and discharging modes of the system. The stability of each charged species is determined by measuring the variation of half-cell potential with time. The spectra of the electrolytes are recorded before and after charging of the system. The effect of atmosphere on the charged species has also been investigated.

    • Photogalvanic generation of dihydrogen by water splitting using MoS42− as catalyst

      R G Bhattacharyya D P Mandal K K Rohatgimukherjee

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      A 4% solar energy efficiency has been achieved for photogeneration of dihydrogen (H2) using MoS42− as catalyst, when the anode compartment of a photogalvanic cell is illuminated. The generated photocurrent rises slowly with time and reaches a limiting value. Ten hours after the reaction starts, a secondary dark reaction sets in which produces H2 and photocurrent even when the light is switched off. Possible mechanisms in both cases have been suggested.

    • Biomimetic routes for photosplitting of water

      K K Rohatgi-Mukherjee A B Chatterjee B B Bhowmik S C Bera Manorama Bhattacharya J Chaudhury B Manna

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      Natural photosynthesis involves splitting of water into O2 and H2 by thermodynamically uphill electron transfer using photon energy absorbed by green chlorophylls and other light-absorbing molecules in leaf chloroplast. It is a multiphotonmultielectron-photosensitized reaction. The artificial photocatalytic system must mimic both the function and the scheme of natural photosynthesis, to bring about this uphill electron transfer. The key concept is organization to prevent back electron transfer. A preliminary report of the attempts made in our laboratory to promote vectorial electron transfer by using various techniques such as PEC cells and liposomes, using chlorophylls isolated from spinach leaves as well as synthesis of their analogues porphyrins synthesized in the laboratory is presented.

    • Hydrogen photoproduction by algae and higher plants: Optimal conditions for polarographic determination

      G Kulandaivelu V Ravi A Thangaraj

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      Photosynthetic H2 production capacity has been studied using a H2 sensitive electrode in green and blue-green algae, higher plant cells and chloroplasts and photosynthetic bacteria. Among the cell types tried,Anacystis showed the maximum rate of H2 production. All the cell types require either an electron acceptor or a reductant (sodium dithionite) for H2 production. In the presence of an electron acceptor or reductant H2 production was observed even in unadapted cells. Cultures ofAnacystis grown for a maximum period of 70 days showed a high rate of H2 production up to 40 days. The light saturation curves and pH optima for H2 production were similar to that of O2 evolution in the cell types studied.

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