Photoanode In Photoelectrochemical Cell Research Articles

Ultrasound-Assisted Preparation of Semiconductor/Polymer Photoanodes and Their Photoelectrochemical Properties

Metal oxide-loaded poly(butylmethacrylate) films were sonochemically prepared and used as photoanodes in photoelectrochemical cells. A small quantity of polyaniline was added during the latex synthesis to facilitate the transport of charge carriers. The semiconductor metal oxides used in this study were ZnO, TiO2, and Bi2O3/ZrTiO4. The performance of the photoanodes was evaluated by measuring the short-circuit current (Isc) and open-circuit potential (Voc) in four different electrolytes. It was found that photocurrents generated were directly proportional to the amount of metal oxide loading, whereas a decrease in photocurrent was observed with an increase in the thickness of the latex film. At 0.4 g loading, Bi2O3/ZrTiO4 latex showed the highest photocurrent of 0.9 μA/cm2 in aqueous formic acid solution. On the basis of the photocurrents generated, the performance of the three different oxide films is as follows: Bi2O3/ZrTiO4 > ZnO > TiO2.

Effect of temperature on various properties of photoelectrochemical cell

Abstract Zinc sulphide photoelectrode have been synthesized by dip method. Zinc sulphide acts as photoanode in photoelectrochemical cells. The photoanode annealed up to 473 K. The configuration of fabricated cell is n-ZnS|NaOH (1 M) + S (1 M) + Na 2 S (1 M)|C (graphite) . The various performance parameters were examined with respect to annealed temperature. It is found that fill factor and efficiency are maximum for photoelectrode annealed at 473 K. This is due to low resistance, high flat band potential, maximum open circuit voltage as well as maximum short-circuit current. The barrier-height was examined from the temperature dependence of the reverse saturation current. The utility of this work is in improving the efficiency of photoelectrochemical cell.

Growth by Molecular Beam Epitaxy of GaNAs Alloys with High As Content for Potential Photoanode Applications in Hydrogen Production

AbstractWe have studied the low-temperature growth of GaNAs layers on sapphire substrates by plasma-assisted molecular beam epitaxy. We have succeeded in achieving GaN1-xAsx alloys over a large composition range by growing the films at temperature much below the normal GaN growth temperatures with increasing the As2 flux as well as Ga:N flux ratio. We found that the alloys with high As content x>0.1 are amorphous. Optical absorption measurements reveal a continuous gradual decrease of band gap from ˜3.4 eV to ˜1.4 eV with increasing As content. The energy gap reaches its minimum of ˜1.4 eV at the x˜0.6-0.7. For amorphous GaAsN alloys with x<0.3 the composition dependence of the band gap follows the prediction of the band anticrossing model developed for dilute alloys. This suggests that the amorphous GaN1-xAsx alloys have short-range ordering that resembles random crystalline GaN1-xAsx alloys. Such amorphous GaN1-xAsx alloys with tunable electronic structure may be useful as photoanodes in photo-electrochemical cells for hydrogen production.

Photoelectrochemical properties of Nb-doped titanium dioxide

Nb-doped TiO 2 (0–15 at% Nb) polycrystalline specimens were prepared by sol–gel method. The materials were used as photoanode in photoelectrochemical cell to water splitting. Based on the photocurrent experiments, the effects of Nb concentration on incident photon-to-current efficiency (IPCE), flat band potential and overall efficiency of solar energy conversion were discussed. It was found that addition of Nb leads to an increase in solar-to-hydrogen energy efficiency. The maximum energy conversion efficiency has been observed for TiO 2 doped with 1 at% Nb.

Dye cell efficiency

Molybdenum dithiolene complexes with the general formula [MoTp*(NO)(L)], where Tp* = tris(3,5-dimethylpyrazolyl)hydroborate and L = toluene-3,4-dithiolate (L1), 1,2-benzenedithiolate (L2), or 3,6-dichloro-1,2-benzenedithiolate (L3), were found to exhibit the chemical and physical properties required for a photosensitiser in a photoelectrochemical cell. These complexes were characterised using micro-elemental, spectroscopic (IR and UV–vis) and electrochemical analyses. Cyclic voltammetry (CV) was used to determine the oxidation/reduction potentials and to calculate the energy band gap. All of the complexes had an energy band gap in the range 1.45–1.48 eV, which extends far into the visible light region. A TiO2 thin film to be used as a photoanode for photoelectrochemical cells was prepared using the paste technique on a Fluorine-doped Tin Oxide (FTO) plate and characterised using scanning electron microscope (SEM) and X-ray diffractometer (XRD). The [MoTp*(NO)(L)]-doped TiO2 photoanodes were analysed photochemically in a 1.0 M NaOH electrolyte solution using SCE reference and platinum counterelectrodes. The [MoTp*(NO)(L3)]-doped TiO2 photoanode exhibited an increased photoinduced current compared with the undoped TiO2 photoanode. The Cl atoms on the dithiolene group offered a better interaction between the photosensitiser molecule and the TiO2 photocatalyst by providing a means for halogen atom-induced chemical bonding. Based on the band edge calculations and the subsequent photocurrent results, these complexes may be potential photosensitisers for use in the preparation of photoelectrodes for photoelectrochemical cells.

Nanostructured thin films of C60-aniline dyad clusters: electrodeposition, charge separation, and photoelectrochemistry.

Clusters of C60-aniline dyads are deposited as thin films on nanostructured SnO2 electrodes under the influence of an electric field. At low applied DC voltage (<5 V) the clusters in toluene/acetonitrile (1:3) mixed solvent grow in size (from 160 nm to approximately 200 nm in diameter) while at higher voltages (>50 V) they are deposited on the electrode surface as thin films. The C60- aniline dyad cluster films when cast on nanostructured SnO2 films are photoelectrochemically active and generate photocurrent under visible light excitation. These nanostructured fullerene films are capable of delivering relatively large photocurrents (up to approximately 0.2 mA cm(-2), photoconversion efficiency of 3-4%) when employed as photoanodes in photoelectrochemical cells. Both luminescence and transient absorption studies confirm the formation of charge transfer product (C60 anion) following UV/Vis excitation of these films. Photo-induced charge separation in these dyad clusters is followed by the electron injection from C60-anion moiety into the SnO2 nanocrystallites. The oxidized counterpart is reduced by the redox couple present in the electrolyte, thus regenerating the dyad clusters. The feasibility of casting high surface area thin fullerene films on electrode surfaces has opened up new avenues to utilize dyad molecules of sensitizer bridge donor type in light energy conversion devices, such as solar cells.

Photoactive iron pyrite films for photoelectrochemical (PEC) cells

Photoactive iron pyrite (FeS 2) films have been grown by sulfurization of sprayed iron oxide films. The structural properties were studied using X-ray diffraction. The films showed good crystallinity with grain size ≈500 Å. These films have been used as photoanode in photoelectrochemical cells.

An investigation of the electrochemical and photoelectrochemical properties of the cuprous oxide/liquid phase boundary

In view of the possible application of cuprous oxide in solar energy conversion its physical properties and photoelectrochemical behavior of the phase boundary between the Cu 2O and liquid have been investigated. The composition of galvanostatically deposited films is pure Cu 2O, but its structure is disordered. The conductivity is due to carriers hopping between localized energy states. At room temperature thin Cu 2O films behave like n-type semiconductors. On the basis of the experimental data an energy scheme for the thin oxide semiconductor film is given. From the representative voltammograms in the dark and under illumination it could be concluded that the currents are changed under illumination and that photodegradation takes place. Some unusual phenomena are discussed on the basis of the properties of the thin oxide/electrolyte phase boundary where surface effects are more pronounced than in the bulk material. The conversion efficiency of the Cu 2O photoanode in photoelectrochemical cells is below 1%. An analysis of the causes of this poor performance is given.

TiO 2-SiO 2 based photoanodes in photoelectrochemical cells—performance and evaluation studies

The effect of SiO 2 as a coprecipitant on the photochemical behaviour of polycrystalline n-TiO 2 electrode is investigated. It is observed that incorporation of silica into titania based photoanodes improved their photochemical efficiency. XPS and XRD data suggest this improved efficiency may be due to the formation of suboxides of titanium and the improved absorption characteristics of titania anode surface.

ChemInform Abstract: Gallium Phosphide/Gallium Arsenide Phosphide Strained‐Layer Superlattice (SLS) Electrodes. Effect of the Terminating Layer on Photoelectrochemical Properties.

AbstractPairs of SLS's are studied as photoanodes in photoelectrochemical cells.

Luminescent Properties of Cadmium Sulfoselenide Electrodes Prepared by Ion Implantation

Inhomogeneous samples of n‐type have been prepared by implantation of Se+ ions into single‐crystal substrates. When thermally annealed, these samples exhibit photoluminescence (PL) and photoelectrochemical properties characteristic of alloy compositions. The spatial profile of Se has been examined by secondary ion mass spectroscopy (SIMS), electron microprobe analysis, and PL spectra, obtained after successive photoelectrochemical etching treatments. SIMS data indicate the presence of a Se‐containing surface layer, extending ∼0.5 μm into the sample with a peak Se content of about 50%. The PL spectra are dominated by contributions from compositions having up to ∼30% Se content. These samples can be used as photoanodes in photoelectrochemical cells (PEC's) employing aqueous, alkaline, (di) selenide electrolyte. Photoaction spectra are consistent with contributions from alloys of up to ∼35% Se content. The PL intensity of the samples is quenched in passing from open circuit (∼−1.5V vs. SCE) to a potential near short circuit (−1.0V), but the spectral distribution is unaffected. The electroluminescence (EL) of the samples, obtained in aqueous, alkaline, peroxydisulfate electrolyte, is similar to the PL in spectral distribution.

Gallium phosphide/gallium arsenide phosphide strained-layer superlattice electrodes: effect of the terminating layer on photoelectrochemical properties

Pairs of strained-layer superlattices (SLS's) have been studied as photoanodes in photoelectrochemical cells (PEC's) employing aqueous ditelluride electrolyte. The SLS's are comprised of alternating layers of n-GaP and a n-GaAs/sub 1-x/P/sub x/ alloy (x approx. 0.6) with a total of 25 periods; the pairs are grown under matched conditions with one member terminating in the alloy composition and its counterpart in GaP. The pairs possess common bulk properties but different surfaces. While all samples examined gave good efficiencies for the conversion of 458- and 514-nm ultraband gap (E/sub g/ approx. 2.1 eV) monochromatic light to electricity (in some cases approx. 10%), the alloy-terminated samples gave consistently better efficiencies. Bulk and surface properties that may contribute to the superiority of the alloy-terminated samples are discussed. Photoaction spectra reveal the GaP-terminated samples to have an enhanced photoresponse near the band gap energy. Evidence that this feature is surface-localized is presented. Attempts to modulate the photoelectrochemical properties of a given SLS electrode by removing its original terminating layer are discussed.

Photoelectrochemcal properties of Zr xTi 1−xNb 2O 7 mixed oxides

The suitability of Zr xTi 1 −xNb 2O 7 mixed oxides as photoanodes in photoelectrochemical cells is investigated. The mixed oxides are not as suitable as the end members. ZrNb 2O 7 can be expected to be a promising candidate from the point of view of stability.

Sn 1−x Pb x O 2 sputtered thin films as photoanodes for photoelectrochemical cells

Pb x Sn 1−x O 2 thin films have been prepared by glow discharge. These films have been characterized by X-ray and microprobe analysis. The photoelectrochemical behaviour shows anodic and cathodic corrosion either in the dark or under illumination. The onset of photocurrent is pH dependant. Photocurrent versus the wavelength is shifted to the visible range of the spectrum when lead content increases.

Effect of zinc composition on properties on PEC cells based on sprayed Cd1−x Zn x S films

Polycrystalline Cd1−x Zn x S films were prepared by spray pyrolysis technique, both on conducting and non-conducting glasses. These films were used as photoanodes in photoelectrochemical cells. The optical and electrical properties of these cells are studied and the effect of zinc composition on these properties is revealed.

Effect of temperature on the performance of photoelectrochemical cells formed with TiNi oxide electrodes

TiNi oxide electrodes are formed by oxidizing TiNi alloys of various compositions in air at different temperatures. These electrodes have been used as photoanodes in photoelectrochemical cells. The effect of temperature on these cells is studied by making measurements on the speed of response, spectral response and photovoltaic output characteristic of the cells. It is found that an optimum temperature exists for these cells. The operation of these cells at elevated temperature therefore means an increase in the conversion efficiency as the infrared region of the solar spectrum may be utilized for heating these cells.

N-CuInSe2/polysulfide photoelectrochemical solar cells

We report that n-type single crystals of n-CuInSe2 in aqueous polysulfide solution exhibit high quantum efficiencies of 0.8–0.9 in the wavelength region between 600–1150 nm when used as photoanodes in photoelectrochemical cells. Photocurrents of 28 mA/cm2 were measured on a ’’winter’’ day in Rehovot (71 mW/cm2) which corresponds to 40 mA/cm2 under AM1 (Air Mass 1) conditions (100-mW/cm2 sunlight). Stability tests of n-CuInSe2 photoanodes (20 000-C/cm2 photocharge passage) at short circuit current densities of 40 mA/cm2 have shown no deterioration whatsoever of the measured photocurrents.

Luminescent Photoelectrochemical Cells: VII . Photoluminescent and Electroluminescent Properties of Cadmium Sulfo‐Selenide Electrodes

Samples of single crystal, n‐type emit when excited with ultra‐bandgap excitation. The 295 K bandgaps monotonically decrease with from ∼2.4 eV for to ∼1.7 eV for . Photoluminescence (PL) spectra are sharp and have band positions which vary nearly linearly with composition: . The energetic proximity to the bandgap, temperature dependence, and decay times are all consistent with a description of the PL as edge emission. Measured PL efficiencies, , are ∼10−4 in air. When the samples are used as photoanodes in photoelectrochemical cells (PEC's) employing aqueous polysulfide electrolyte, the emission intensity can be quenched by the passage of photocurrent. The extent of quenching can be correlated with the photocurrent quantum efficiency. Electroluminescence (EL) can be initiated by using the samples as dark cathodes in aqueous, alkaline, peroxydisulfate electrolyte at potentials cathodic of ∼−0.9 to −1.1V vs. SCE. The EL spectral distribution for a given sample is similar to that observed in PL experiments and indicates that the same emissive excited state is involved. At high resolution EL and PL spectra can differ in a manner which shows evidence of self‐absorption effects: The EL spectra are slightly broader than their PL counterparts with the spectral mismatch almost exclusively in the high energy tail. This suggests that EL occurs, on average, nearer the semiconductor‐electrolyte interface. Measured EL efficiencies exceed 10−4 or 10−5 at −1.50V vs.SCE, but are smaller near the EL threshold potentials. Comparisons with values are discussed.

Models for the Photoelectrolytic Decomposition of Water at Semiconducting Oxide Anodes

Surface states at semiconducting interfaces are believed to play an important role in charge transfer and thereby the efficiency of photoelectrochemical processes at such interfaces. Theoretical calculations were therefore performed using the SCF‐Xα‐SW method to determine the position and character of surface states at various characteristic interfaces. At the interface, antibonding surface states were found which when occupied would explain the experimentally observed dissociation of water into hydroxyl groups at n‐type semiconducting surfaces. Similarly, antibonding surface states were found at the interface which when occupied would tend to destabilize the OH bond. A likely mechanism for the dissociation of water and decomposition of certain photoanodes in photoelectrochemical cells based on the above results is presented. The effects of surface reconstruction at heavily reduced surfaces on the validity of our calculations are also discussed.