Surface Of Semiconductor Electrode Research Articles

Investigation of a Novel Rhenium Disulfide Electrocatalyst By Sum Frequency Generation Vibrational Spectroscopy

The heterogeneous electrocatalysis is developing as a promising approach to overcome the energy regeneration issues around the world. It is well known for the enhancement of stability, selectivity, and productivity for the catalytic reaction, especially in the electrocatalytic reaction. By binding electrocatalytic molecules onto the metal or semiconductor electrode surface, CO2 reduction reaction or H2 evolution reaction can be more efficient. However, the behaviors of catalysts during heterogeneous electrocatalysis are always triggering people’s interest in understanding how interfacial electric field interacts with molecules. In this paper, a novel rhenium -based CO2 reduction electrocatalyst Re(SSbpy)(CO)3Cl was synthesized and attached to polycrystalline gold film electrode. By probing the symmetric CO stretching mode with potential dependent SFG vibrational spectroscopy, the Stark shifting rate of 7~8 cm-1/V under applied bias was revealed, indicating a weak correlation between symmetric CO stretching dipole and interfacial electric field. In addition, DFT calculation represented that this molecule tended to be adsorbed on the gold surface with nearly zero tilt angle with a great agreement to spectroscopic results.

Why and How Carbon Dioxide Conversion to Methanol Happens on Functionalized Semiconductor Photoelectrodes.

Functionalization of semiconductor electrode surfaces with adsorbed 2-pyridinide (2-PyH-*) has been postulated to enable selective CO2 photoelectroreduction to CH3OH. This hypothesis is supported by recent estimates of sufficient 2-PyH-* lifetimes and low barriers for hydride transfer (HT) to CO2. However, the complete mechanism for reducing CO2 to CH3OH remained unidentified. Here, vetted quantum chemistry protocols for modeling GaP reveal a pathway involving HTs to specific CO2 reduction intermediates. Predicted barriers suggest that HT to HCOOH requires adsorbed HCOOH* reacting with 2-PyH-*, a new catalytic role for the surface. HT to HCOOH* produces CH2(OH)2, but subsequent HT to CH2(OH)2 forming CH3OH is hindered. However, CH2O, dehydrated CH2(OH)2, easily reacts with 2-PyH-*, producing CH3OH. Further reduction of CH3OH to CH4 via HT from 2-PyH-* encounters a high barrier, consistent with experiment. Our finding that the GaP surface enables HT to HCOOH* explains why the primary CO2 reduction product over CdTe photoelectrodes is HCOOH rather than methanol, as HCOOH does not adsorb on CdTe and so the reaction terminates. The stability of 2-PyH-* (vs its protonation product DHP*), the relative dominance of CH2(OH)2 over CH2O, and the required desorption of CH2(OH)2* are the most likely limiting factors, explaining the low yield of CH3OH observed experimentally.

Hydride Shuttle Formation and Reaction with CO2 on GaP(110).

Adsorbed hydrogenated N-heterocycles have been proposed as co-catalysts in the mechanism of pyridine (Py)-catalyzed CO2 reduction over semiconductor photoelectrodes. Initially, adsorbed dihydropyridine (DHP*) was hypothesized to catalyze CO2 reduction through hydride and proton transfer. Formation of DHP* itself, by surface hydride transfer, indeed any hydride transfer away from the surface, was found to be kinetically hindered. Consequently, adsorbed deprotonated dihydropyridine (2-PyH- *) was then proposed as a more likely catalytic intermediate because its formation, by transfer of a solvated proton and two electrons from the surface to adsorbed Py, is predicted to be thermodynamically favored on various semiconductor electrode surfaces active for CO2 reduction, namely GaP(111), CdTe(111), and CuInS2 (112). Furthermore, this species was found to be a better hydride donor for CO2 reduction than is DHP*. Density functional theory was used to investigate various aspects of 2-PyH- * formation and its reaction with CO2 on GaP(110), a surface found experimentally to be more active than GaP(111). 2-PyH- * formation was established to also be thermodynamically viable on this surface under illumination. The full energetics of CO2 reduction through hydride transfer from 2-PyH- * were then investigated and compared to the analogous hydride transfer from DHP*. 2-PyH- * was again found to be a better hydride donor for CO2 reduction. Because of these positive results, full energetics of 2-PyH- * formation were investigated and this process was found to be kinetically feasible on the illuminated GaP(110) surface. Overall, the results presented in this contribution support the hypothesis of 2-PyH- *-catalyzed CO2 reduction on p-GaP electrodes.

Inferring Protonation States of Hydroxamate Adsorbates on TiO2 Surfaces

We explore the protonation states of benzohydroxamic acid adsorbates bound to the {101} facet of TiO2 anatase by using a combination of density functional theory, simulations of UV–vis spectra based on a tight-binding Hamiltonian, and direct comparisons to experimental measurements. We find that the characteristic red-shifted spectrum of nonmethylated, relative to the methylated, hydroxamic acids can only be explained by proposing a monodeprotonated monodentate mode as the main adsorption mode. The reported analysis suggests a simple, yet general, spectroscopic method based on UV–vis absorption measurements and tight-binding calculations for inferring changes of pKa of molecular adsorbates interacting with semiconductor electrode surfaces.

Simultaneous Measurement of Absorbance and Quantum Yields for Photocurrent Generation at Dye-Sensitized Single-Crystal ZnO Electrodes

It is often assumed that the photoresponse or incident photon-to-current conversion efficiency (IPCE) spectrum of a sensitized semiconductor electrode is directly correlated with the amount of sensitizing species present on the semiconductor surface. In reality, the various forms of adsorbed species, such as dye aggregates or dye molecules bound to different adsorption sites, such as terrace edges, can have significantly different electron injection yields and carrier recombination rates. To provide information about the amounts of the various adsorbed dye species and their effectiveness as sensitizers, we report the simultaneous acquisition of IPCE and attenuated total reflectance (ATR) UV-vis spectra for a thiacyanine dye bound to a single-crystal oxide semiconductor electrode surface. ZnO single crystals were fashioned into internal-reflection elements to act both as a waveguide for the internally reflected probe beam for UV-vis spectra and as the substrate for dye sensitization using dyes with distinct spectral signatures for monomers and aggregates. Strong agreement was observed between the quantum efficiency and ATR UV-vis spectra, suggesting that, under the conditions employed, both monomers and aggregates of the dye studied generate photocurrent with the same efficiency.

Formation of low resistance gas state near the surface of semiconductor electrode in pre-breakdown regime

The electrical conductivity of a thin gas discharge gap (d = 60 µm) filled with atmospheric air at 60 Torr pressure and room temperature was investigated. Current–voltage characteristics of the device when both the electrodes are metals and when one of the electrodes is a high resistivity GaAs semiconductor were measured. It is shown that in the device with the semiconductor electrode, the current is registered before the breakdown of gas. The value of pre-breakdown current depends on experimental conditions: it increases drastically if gas is subjected to breakdown before the measurements. Thus, the device has a memory effect. The value of memory effect depends on the value of the ionization current and does not depend on the polarity of the applied voltage. The effect is absent in a device with two metallic electrodes, and the effect disappears after the pumping of the gas down to 0.1 Torr. The obtained results can be explained on the basis of diffusion–drift type equilibrium of charges taking into account the charging of the semiconductor near the surface. The latter is the guarantee of the stability of residual pre-breakdown current in the gas.

Highly Hydrophilic Surfaces of Cathodically Polarized Amorphous TiO2 Electrodes

We have investigated the change in surface wettability of n-type semiconductor electrode surfaces induced by cathodic polarization. While the wettability of polycrystalline anatase electrode surfaces did not change remarkably regardless of the electrode potential, the surface of amorphous electrodes became highly hydrophilic under cathodic conditions without UV light irradiation. We conclude that the increase in the number of hydroxyl groups due to electron addition to the near-band-edge trap sites accompanied by proton intercalation is responsible for the present hydrophilic conversion under cathodic conditions. © 2001 The Electrochemical Society. All rights reserved.

Integrating photoelectrochemical semiconductor sensor for sulphide ion determination

A novel approach to the determination of small amounts of S 2− in aqueous solution based on the photoelectrochemical dissolution of semiconductor metal sulphide deposit arising at the surface of semiconductor electrode via exchange reaction is proposed. The potentialities of this approach are demonstrated using coulometric CdO-based photoelectrochemical sensor, which operates in an accumulation mode and exhibits a linear dependence of analytical signal (photocharge) on S 2− concentration in the range 3.4×10 −6 to 4.4×10 −9 M.

Vanishing of Current-Doubling Effect in Photooxidation of 2-Propanol on TiO2 in Solutions Containing Fe(III) Ions

When organic compounds such as 2-propanol are in aqueous solutions and are photooxidized on the surface of semiconductor electrodes, the current quantum efficiency can reach close to 200% (current-doubling effect). However, we found that the current-doubling effect in the photooxidation of 2-propanol on TiO2 electrodes disappeared in solutions containing Fe(III) ions. From the analyses of the products, we found that acetone was produced in quantitative correlation to the photocurrent, and that practically no Fe(II) ions were generated in the solution. We also found that Fe(II) ions were not oxidized at a TiO2 photoanode in a solution containing Fe(III) ions, while they were oxidized in quantitative correlation to the photocurrent in the solution without Fe(III) ions. These results refuted the possibility that Fe(III) ions accepted electrons from the oxidation intermediates of 2-propanol. The plausible reason for the disappearance of the current-doubling effect is that 2-propanol is oxidized by two holes o...

Electrochemical impedance spectroscopy at semiconductor electrodes: the recombination resistance revisited

The correspondence between an electron-hole recombination step at the semiconductor electrode surface and the electrical impedance spectrum is reconsidered. It is shown theoretically that the well-known recombination resistance is identical to the faradaic resistance of a direct capture process. This fact is illustrated experimentally, using the reduction of methylviologen at n-GaAs as an example. A recombination-like resistance is hence not typical for hole injection steps in cathodic reduction reactions at n-type semiconductors. The consequences of this conclusion to the interpretation of electrical impedance spectra based on reaction models are discussed.

Ultrasound in photoelectrochemistry: A new approach to the enhancement of the efficiency of semiconductor electrode processes

A novel photoelectrochemical experiment which simultaneously allows the illumination of a TiO 2 semiconductor electrode surface and the application of power ultrasound emission is described. The horn probe of an immersion horn transducer is modified by an oxide coated titanium tip and placed in a conventional three electrode electrochemical cell which allows light from a monochromated source to be focussed onto the electrode surface. Well-defined photocurrents are observed in aqueous media and for the photoinduced oxidation of water in acetonitrile and of 2,4-dichlorophenol in acetonitrile. The effect of ultrasound is to shift the observed photocurrent responses to more negative potentials and therefore to enhance the observed processes. Several possible interpretations associated with the complex effects induced by ultrasound are considered and a model based mainly on the extreme change of mass transport at the semiconductor/solution interface is suggested. Considerably enhanced performance for non-Nernstian processes, such as those observed in photoelectrochemical reactions at semiconductor electrodes, can be achieved in the presence of ultrasound.

A kinetic equation for minority carriers at the surface of semiconductor electrodes

Mmorlty carrier relaxation and surface state relaxation are the two time dependent coupled processes that occur at semiconductor interfaces [1,2] Surface state relaxation 1s usually viewed as purely temporal with no spatial extension mto the bulk and hence 1s modelled as a first order kmetlc equation [31 However, mmorlty carrier relaxation 1s a volume process and Its time behavlour at the surface needs to be derived from the transport equation usmg appropriate boundary condltlons In the presence of a space-charge layer, whether it 1s possible to derive a kinetic form or not for the minority carriers 1s a question that has not been addressed so far Such kmetlc forms have been assumed previously, but as they were not rigorously derived, the order of magnitude of the length parameter needed to project a volume process at the surface has remained speculative [1,4] In this note, we report some of the results concerning minority carrier relaxation at the surface, whose general form 1s given by an integral equation which can be reduced to a simple kinetic form under certain condltlons From this kinetic equation we obtain the exact form of the earlier mentioned length parameter and more importantly the potential dependent rate constant for the mmorlty carrier relaxation, as we have included space-charge effects The rate of relaxation of the integral of the mmorlty carners m the semiconductor electrode can be shown to be approximately the same as that of the minority carriers at the surface [5] As a result the potential dependence of transient photomduced microwave conductlvlty [61 and the time resolved fluorescence signals [71, which are proportional to the total mmorlty carrier concentration, can be understood from the rate constant of the kinetic equation of mmorlty carriers at the surface

Application of scanning tunnelling microscopy to semiconductor/electrolyte interfaces

To study the application of in situ electrochemical scanning tunnelling microscopy (STM) measurements at semiconductor electrode surfaces, the tip current has been measured as a function of the semiconductor potential. It was demonstrated that the surface treatment affects very strongly the potential window for STM measurements on n-GaAs. At an ‘etched’ n-GaAs electrode, the tip current was maintained at a preset value when the potential of n-GaAs was more negative than –250mV and more positive than +700 mV. STM images of n-GaAs in the two potential regions are presented to confirm that imaging is really possible in these regions. While no surface change was observed in the negative-potential region, the surface morphology changed with time in the positive-potential region. If the surface was treated with RuCl3 solution, the preset tip current flowed when the potential was more negative than –100 mV and more positive than +100 mV. On the other hand, if the surface was treated with (NH4)2S–S solution, the preset tip current flowed only when the potential was more negative than –1000 mV, which is very close to the flat-band potential. These results are explained using an energy diagram and the importance of the surface-state density for STM characterisation is stressed. The ‘ruthenium treatment’ and the ‘sulphur treatment’ are considered to introduce and remove, respectively, the surface states. Results for CdS are also presented.

The conversion of light and water to hydrogen and electric power

The effect of etching the electrode surface and of the deposition of submonolayer quantities of metal on the semiconductor electrode surface has been examined. The experimental observations show that the rate of reaction (H 2 evolution) is determined by the charge transfer rate across the metal-solution interface. Recent experiments also show that the photocorrosion of small band gap non-oxide semiconductor photoanodes can be prevented by depositing suitable conducting transparent coatings on the electrode surface. By using the electrocatalysed photocathodes and protected photoanodes, high efficiencies for the photoelectrolysis of water can be achieved.

Photoelectrochemical Polymerization of Pyrrole on TiO2 and Its Application to Conducting Pattern Generation

Polymerization of pyrrole occurred on an irradiated surface of semiconductor electrode in aqueous solutions of pyrrole, when the electrode potential was set between −0.6 and +1.5V vs. SCE. The conductivity of deposited polypyrrole film (as grown, in the doped state) was ca. 1S cm−1. Electrochemical undoping of the film gave conductivity of . The deposition rate for the photoelectrochemical polymerization, 0.6 μm per 100 mC cm−2, was three times that for electrochemical polymerization, 0.2 μm per 100 mC cm−2. From the relationship between the charge passed through the circuit and the absorbance of the film, it was revealed that the current efficiency for the photoelectrochemical polymerization and that for the electrochemical polymerization are almost the same. It was concluded that coarseness and the relatively low doping level of the film were the reasons for the relatively low conductivity of the photoelectrochemically deposited films. Conducting polypyrrole patterns with a line width of 45 μm were formed on the electrode surface by area selective irradiation of the electrode.

Surface-enhanced resonance Raman spectroscopy of adsorbates on semiconductor electrode surfaces. 2. In situ studies of transition metal (iron and ruthenium) complexes on silver/gallium arsenide and silver/silicon

Surface-enhanced resonance Raman spectroscopy of adsorbates on semiconductor electrode surfaces. 2. In situ studies of transition metal (iron and ruthenium) complexes on silver/gallium arsenide and silver/silicon

Electroreflection Measurements on Semiconductor/Electrolyte Interfaces to Determine the Voltage Distribution

The electroreflectance signal from a semiconductor electrode surface is sensitive to the magnitude of the space charge. It is used to determine the voltage distribution between the space‐charge layer and the Helmholtz double layer at an electrode/electrolyte interface. In this paper, the first of two, we describe the experimental arrangements and measurements of the electroreflectance spectra for and under anodic and cathodic bias. Important features in the spectra are found to be in agreement with existing theories. Flatband values inferred from the electroreflectance spectra are in agreement with those from Mott‐Schottky plots. The effects of Fermi level pinning on the electroreflectance spectra are demonstrated with .

Surface-enhanced Raman spectroscopy of adsorbates on semiconductor electrode surfaces: tris(bipyridine)ruthenium(II) adsorbed on silver-modified n-gallium arsenide(100)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSurface-enhanced Raman spectroscopy of adsorbates on semiconductor electrode surfaces: tris(bipyridine)ruthenium(II) adsorbed on silver-modified n-gallium arsenide(100)Richard P. Van Duyne and Jeanne P. HaushalterCite this: J. Phys. Chem. 1983, 87, 16, 2999–3003Publication Date (Print):August 1, 1983Publication History Published online1 May 2002Published inissue 1 August 1983https://doi.org/10.1021/j100239a004RIGHTS & PERMISSIONSArticle Views372Altmetric-Citations68LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

The Investigation of Current Doubling Reactions on Semiconductor Photoelectrodes by Temperature Change Measurements

Current doubling effects in the photoanodic reactions of or on n‐type semiconductor electrodes (, , and ) and the photocathodic reaction of on a p‐type semiconductor were studied by the measurement of the temperature change of a semiconductor electrode surface. The results of the temperature change measurements show that these photoelectrode reactions proceed with quantum efficiencies greater than 1 but less than 2. The temperature changes are interpreted in terms of the current doubling process.

Intrinsic Quantum Efficiencies of Semiconductor Photoelectrodes Obtained by Temperature Measurement

Abstract Quantum efficiencies of photoelectrochemical reactions on n-type and p-type semiconductor electrodes can easily be determined by the measurement of temperature changes of the surface of semiconductor electrodes by use of thermistors. The quantum efficiencies are intrinsic, since only the absorbed light quanta contribute to temperature change. The merits of the method, simplicity and applicability to the semiconductor of large surface reflectance, are discussed. The intrinsic quantum efficiencies were compared with those obtained by the usual chemical actinometric method.