Photoelectrochemical and impedance spectral studies on electrodeposited (CdGa)Se films

Polycrystalline thin films of (CdGa)Se of variable composition were synthesised by the electrochemical codeposition process. Characterization of these electrodeposits has been carried out on the basis of photoresponsiveness and photoaction spectral studies. Impedance measurements were carried out to have an estimate of the effect of progressive inclusion of Ga on the corrosion behaviour of the electrodeposits. X-ray diffraction and scanning electron microscopic studies have also been carried out.     

Photoelectrochemical properties of the dilute magnetic semiconductor Cd0.95Mn0.05Se

The dilute magnetic semiconductor Cd_0.95Mn_0.05Se was investigated as a photoelectrode in a photoelectrochemical cell. It is found that a short photoelectrochemical etching produces the highest photoresponse of this material. The effective energy gap is found to be higher than expected by about 130 meV. This observation can be attributed to the onset of the internal d-d transitions in the Mn in or to some nonuniformities in the alloy composition.     

Photoelectrochemical studies on acid-doped polyaniline as sensitizer for TiO2 nanoporous film

Acid-doped polyaniline (PAn) as sensitizer for TiO₂ nanoporous film was investigated using electrochemical and photoelectrochemical methods. The photocurrent generation of TiO₂ nanoporous film sensitized by PAn extends into visible and infrared regions, and a maximum value appears in the region of 600–700 nm. The mechanisms of sensitization have been discussed in this paper.     

Photoelectrochemical studies on galvanostatically formed cadmium selenide films using mixed solvents

Galvanostatic deposition technique has been used for the formation of cadmium selenide films using water and dimethyl sulphoxide mixtures of variable composition. For photoelectrochemical characterization of these electrodeposits, photoelectroconvertibility and photoaction spectral studies have been carried out using I₂/I₃⁻ and [Fe(CN)₆]⁻³/[Fe(CN)₆]⁻⁴ redox systems. Resistance of these photoelectroactive films towards electrochemical corrosion has also been investigated on the basis of current–voltage studies using Tafel plots.     

Photoelectrochemical studies of nanocrystalline TiO2 co-sensitized by novel cyanine dyes

Pentamethylcyanine derivative (A), trimethylcyanine derivative (B) and their mixtures (AB) were used as sensitizers in nanocrystalline TiO₂ solar cells to improve photoelectric conversion efficiency. It was found that the aggregates of the cyanine dyes were efficient in light harvesting and that the mixture of A and B could be employed to sensitize the solar cell over the entire visible spectrum. The sensitizing properties of three mixed dyes with different A-to-B ratio were systematically studied, and it was found that A1B3 (A:B=1:3 V/V)-sensitized solar cell generated the highest photoelectric conversion yield of 3.4%. The effect of co-adsorption of A and B on their aggregation behavior and photosensitization was also investigated. Co-sensitization was found to suppress the aggregation and affect the sensitization performance profoundly.     

Photoelectrochemical studies of chemically deposited nanocrystalline p-type HgS thin films

Nanocrystalline mercury sulfide (HgS) thin films were deposited by chemical bath deposition (CBD) method onto the glass and fluorine doped tin oxide (FTO) coated glass substrate from an aqueous alkaline bath (pH  8) at room temperature (300 K). Mercuric acetate and thiourea were used as Hg²⁺ and S²⁻ ion sources, respectively. The photoelectrochemical (PEC) studies of HgS films were carried out, and the nanocrystalline films were found to be photoactive in polyiodide solution. The PEC cell configuration was p-HgS/0.1 M (KOH–KI–I₂)/C. From the current–voltage (I–V) characteristics, it is concluded that the HgS films are of p-type electrical conductivity. The photovoltaic output characteristics were used to calculate the fill factor (ff) and solar conversion efficiency (η). The low value of η may be due to the high value of series resistance (R_s) and interface states in the cell, which are responsible for the recombination mechanism.     

Photoelectrochemical studies on galvanostatically formed multiple band gap materials based on CdSe and ZnSe

The preparation of some multiple band gap semiconductor films based on CdSe and ZnSe has been carried out using galvanostatic electrochemical codeposition technique to investigate their photoelectrochemical characteristics on the basis of photoelectroconvertibility and photoaction spectral studies using I₂/I₃⁻ and [Fe (CN) ₆]³⁻/[Fe (CN) ₆]⁴⁻ redox couples. These composite systems show substantially improved photoelectrochemical properties compared to the constituent CdSe and ZnSe films prepared under comparable experimental conditions. These multiple band gap films were also found to exhibit enhanced resistance towards electrochemical corrosion.     

Photoelectrochemical studies of Cu2O Photoelectrode coated with Au and SiO thin films

An attempt has been made to stabilize the photocurrent in a photoelectrochemical cell by depositing thin Au and SiO films onto the Cu₂O photoelectrode. In case of Au deposition, the photocurrent was either quenched or reduced. This may be the cause of insufficient formation of surface states in the electrode-electrolyte interfaces. In a Sio deposited photoelectrode, its effect was to decrease the quantum efficiency of a fresh sample, however, this deposition does not affect the value obtained for the band gap at 2.11 eV for an uncoated sample. It may be interpreted that the observed deterioration is not due strictly to surface effects or chemical reaction at the surface.     

Photoelectrochemical performance of sprayed n-CdIn2Se4 photoanodes

Cadmium indium selenide thin films have been synthesized by spraying mixture of equimolar solution concentrations of cadmium chloride, indium trichloride and selenourea in aqueous media onto preheated FTO coated glass substrates at optimized substrate temperature and solution concentration. The photoelectrochemical cell configuration of n-CdIn₂Se₄/(1 M NaOH + 1 M Na₂S + 1 M S)/C has been used for investigate the current-voltage characteristics under dark and white light illumination, photovoltaic output, spectral response, photovoltaic rise and decay characteristics. It reveals the film of CdIn₂Se₄ exhibits n-type conductivity. The junction quality factor in dark (n_d) and light (n_l), series and shunt resistance (R_s and R_sh), fill factor (FF) and efficiency (η) for the cell have been estimated. Gartner’s model was used to calculate minority carrier diffusion length and donor concentration (n_D). The observed efficiency and FF of PEC solar cell is 1.95% and 0.37% respectively. Mott-Schottky plot shows the flat-band potential (V_fb) of CdIn₂Se₄ films is −0.655 V/SCE.     

Photoelectrochemical studies of the junction between poly[3-(4-octylphenyl)thiophene] and a redox polymer electrolyte

The photoelectrochemical properties of all-solid-state photoelectrochemical cell constructed from a conjugated polymer poly[3-(4-octylphenyl)thiophene] and an amorphous poly(ethylene oxide) complexed with iodide/triiodide redox couple were studied. In order to develop flexible photoelectrochemical cells, we have used a transparent polymeric metal, doped poly(3,4-ethylenedioxythiophene), as a counter electrode. It was shown that poly(3,4-ethylenedioxythiophene) improved the charge transfer between indium tin-oxide and iodide/triiodide redox couple. The spectral response, photocurrent time, and open-circuit voltage and short-circuit current dependence on light intensity have been studied. The photon to electron conversion efficiency obtained was low. The photocurrent and photovoltage dependence studies on light intensity indicate exciton recombination and/or traps as limiting factors.     

Photoelectrochemical evaluation of undoped and C-doped CdIn2O4 thin film electrodes

Undoped and C-doped cadmium indate (CdIn₂O₄) thin films and powders were synthesized, characterized, and evaluated for photoelectrochemical water splitting. Both undoped and C-doped CdIn₂O₄ samples have cubic lattices, and the presence of carbonate-type species was confirmed in the C-doped sample by XPS. Doping C into CdIn₂O₄ leads to a red shift (but no separate peak) in light absorption and band gap narrowing. The photocurrent densities of CdIn₂O₄ electrodes are at least three-fold greater than either CdO or In₂O₃ electrodes with equivalent film thickness. Carbon doping further improved the photocurrent densities by 33%. The photoelectrochemical performance of C-doped CdIn₂O₄ was optimized with respect to several synthetic parameters, including the C:In molar ratio and glucose concentration in the spray precursor solution, the calcination temperature, and the film thickness. The present work shows that CdIn₂O₄ is a promising photocatalyst and can be suitably doped to improve the electrochemical properties for solar conversion applications.     

Photoelectrochemical properties of spray deposited n-ZnIn2Se4 thin films

Zinc indium selenide (ZnIn₂Se₄) thin films have been prepared by spraying a mixture of an equimolar aqueous solution of zinc sulphate (ZnSO₄), indium trichloride (InCl₃), and selenourea (CH₄N₂Se), onto preheated fluorine-doped tin oxide (FTO)-coated glass substrates at optimized conditions of substrate temperature and a solution concentration. The photoelectrochemical (PEC) cell configuration of n-ZnIn₂Se₄/1 M (NaOH+Na₂S+S)/C has been used for studying the current voltage (I–V), spectral response, and capacitance voltage (C–V) characteristics of the films. The PEC study shows that the ZnIn₂Se₄ thin films exhibited n-type conductivity. The junction quality factor in dark (n_d) and light (n_l), series and shunt resistance (R_s and R_sh), fill factor (FF) and efficiency (η) for the cell have been estimated. The measured (FF) and η of the cell are, respectively, found to be 0.435% and 1.47%.     

Photoelectrochemical performance of Cu-doped ZnIn2S4 electrodes created using chemical bath deposition

A solution growth method for the deposition of Cu-doped zinc-indium-sulfide (ZnIn₂S₄) semiconductor film electrodes is presented. The structural, optical, and photoelectrochemical (PEC) properties of samples were studied as a function of Cu content in samples. The X-ray diffraction pattern of the cubic ZnIn₂S₄ phase of an undoped sample was obtained. No Cu alloys or other binary compounds that included the Cu element were present in Cu-doped ZnIn₂S₄ samples. Images from a scanning electron microscope and atomic ratios of elements in samples obtained from the energy dispersion analysis of X-ray reveal a change in surface morphology and composition for Cu-doped ZnIn₂S₄ samples. The direct energy band gaps, indirect energy band gaps, and thicknesses of samples prepared in this study varied in the ranges 2.07-2.58 eV, 1.60-2.06 eV, and 521-879 nm, respectively. The maximum photoelectrochemical response of samples in 0.5 M K₂SO₄ aqueous solution reached 1.15 mA cm⁻² at an external potential of +1.0 V vs. an Ag/AgCl reference electrode under illumination using a 300-W Xe lamp with light intensity kept at 100 mW cm⁻². The experimental results show that Cu doping with Cu/(Cu+Zn) atomic ratio of 0.08 in samples improves the performance of the ZnIn₂S₄ photoabsorber for PEC applications.     

Photoelectrochemical performance of TiO2 nanotube arrays modified with Ni2P Co-catalyst

Solar-driven water splitting to produce hydrogen is an important solution to the problem of energy shortage and environmental pollution. The photolysis of water to produce hydrogen requires highly efficient and stable photocatalysts, and the anode used as catalyst for oxygen evolution is a bottleneck in this process. In this paper, the a-TNTAs/Ni₂P composite photo-anode was constructed by electrodeposition to anchor the Ni₂P co-catalyst for oxygen evolution at the active site of TiO₂ nanotube arrays (TNTAs). The a-TNTAs/Ni₂P delivered excellent oxygen evolution at a photocurrent density of 1.058 mA cm^-2, an improvement of 2.78 times, 13.2 times, and 15.8 times over a-TNTAs, TNTAs/Ni₂P, and TNTAs photo-anodes, respectively. The Mott-Schottky curve showed that Ni₂P as co-catalyst for oxygen evolution accelerated the rates of separation and transfer of the photogenerated electrons. This research provides a simple and efficient method to promote the OER performance of optical semiconductors.     

Photoelectrochemical characterization of SiC

The current–voltage (I–V) studies for p-SiC in KOH and n-SiC in Na₂SO₃ in a two-electrode configuration indicated that SiC-based photoelectrochemical systems can be a possibility for water splitting. With illumination there is appreciable photocurrent generation at the semiconductor–electrolyte interface, which correspond to water splitting to form hydrogen and oxygen at the respective electrodes. The C–V analysis gave an idea about the flat-band potential and carrier concentration.     

Hydrogen release: In-situ calorimetry studies of NaBH4+2MgH2 doped by ZrF4

In this work, NaBH₄+2MgH₂ doped by ZrF₄ was prepared by the ball-milling method. The structure and the morphology of different systems were characterized by X-ray diffraction and scanning electron microscopy. The thermodynamic properties of hydrogen release were determined by temperature-programmed desorption and differential scanning calorimetry. Hydrogen desorption kinetic properties and hydrogen content were investigated by pressure composition isothermal method. The main objective of this work was to study the relationship between the heat of hydrogen release and the quantity of hydrogen released by In-situ calorimetry measurement. The NaBH₄+2MgH₂+0.1ZrF₄ can release about 7.4 wt.% H₂ by two steps. Firstly, the heat of hydrogen release of the first and the second steps were lower by 480.82 J·g^?1 and 430.8 J·g^?1 than that of NaBH₄+2MgH₂, respectively. And the dehydrogenation enthalpy of NaBH₄+2MgH₂ went from ?243.81 kJ·mol^?1 to ?191.2 kJ·mol^?1. Secondly, the addition of ZrF₄ can improve the hydrogen release kinetic property of NaBH₄+2MgH₂, which can release 5 wt.% H₂ in 2.5 h at 385 °C under 0.01 MPa hydrogen pressure. Therefore, NaBH₄+2MgH₂+0.1ZrF₄ will be a potential candidate as a fuel cell hydrogen supply system.     

Photoelectrochemical analysis of band gap modulated TiO2 for photocatalytic water splitting

In this study the photocatalysis efficiency of titania (TiO₂) is increased by conjugating it with folic acid (FA) molecules through a silane linker (APTMS) layer. Electrochemical testing demonstrated higher negative open circuit potential (OCP) in surface engineered TiO₂ as compared to TiO₂ indicating higher Schottky barrier leading to suppressed electron–hole pair recombination. The photocurrent density under no bias conditions demonstrated 55% increase in modified titania due to lower band gap and suppressed electron hole pair recombination. The mechanism behind higher photocatalytic properties of surface engineered TiO₂ was derived using density functional theory (DFT).     

Photoelectrochemical water oxidation of LaTaON2 under visible-light irradiation

Lanthanum tantalum oxynitride (LaTaON₂) powders were prepared by one-step flux method. LaTaON₂ photoanodes, which are fabricated by using LaTaON₂ powders, are found to exhibit photoelectrochemical activity for overall water splitting. The photocurrent for LaTaON₂ photoelectrodes was ca. 120 μA cm⁻² at 1.5 V vs. reversible hydrogen electrode (RHE) in 1 M NaOH aqueous solutions (pH = 13.6) under AM 1.5 G simulated sunlight irradiation (100 mW cm⁻²). The photocurrent of LaTaON₂ photoelectrode from back-side illumination is much larger than that from front-side illumination, suggesting that the photoelectrochemical property is mainly limited by poor continuous electron transport in the bulk. Further efforts to ameliorate the electron transport in the bulk of LaTaON₂ photoelectrodes are expected to significantly improve their photoelectrochemical performance.     

Photoelectrochemical studies on [MnMoO2(NCS)(Ox)3(H2O)2] (Ox=8‐quinolinol): a novel system for solar energy conversion

Photoelectrochemical studies were carried out on [MnMoO₂(NCS)(Ox)₃(H₂O)₂] {Ox=8‐quinolinol} complex in aqueous dimethylformamide medium in a Honda cell. The system developed a maximum potential of 335 mV when exposed to visible light at 30°C and was found to be reversible. The photogalvanic behaviour has been further investigated by varying the pH, temperature and photosensitizers. When a temperature difference between the illuminated and dark half‐cells was maintained, the system generated 410 mV at 60°C. A solid‐state galvanic cell, developed using the complex mixed with tetraethylammonium perchlorate (TEAP), showed a maximum voltage of 25 mV. A sandwich galvanic cell, constructed from transparent tin oxide‐glass/complex/platinum, developed a maximum photovoltage of 88 mV when irradiated with a tungsten halogen lamp. Copyright © 2000 John Wiley & Sons, Ltd.     

Photoelectrochemical properties of AgInS2 thin films prepared using electrodeposition

Ternary silver-indium-sulfide samples were deposited on fluorine-doped tin oxide (FTO) coated glass substrates using a one-step electrodeposition method. A new procedure for the deposition of AgInS₂ samples is reported. The effect of the [Ag]/[In] molar ratio in solution bath on the structural, morphological, and photoelectrochemical properties of samples was examined. X-ray diffraction patterns of samples show that the films are the AgInS₂ phase. The thickness, direct band gap, and indirect band gap of the films were in the ranges 209-1021 nm, 1.82-1.85 eV, and 1.44-1.51 eV, respectively. The carrier densities and flat-band potentials of films obtained from Mott-Schottky and open-circuit potential measurements were in the ranges of 4.2×10¹⁹-9.5×10¹⁹ cm⁻³ and −0.736 to −0.946 V vs. the normal hydrogen electrode (NHE), respectively. It was found that the samples with molar ratio [Ag]/[In]=0.8 in solution bath had a maximum photocurrent density of 9.28 mA/cm² with an applied bias of +1.0 V vs. an Ag/AgCl electrode in contact with electrolyte containing 0.25 M K₂SO₃ and 0.35 M Na₂S. The results show that high-quality AgInS₂ films can be deposited on FTO-coated glass substrates for photoelectrochemical (PEC) applications.