The photocurrent‐time dependence observed during experiments of water photo‐oxidation at an single crystal, as a function of the applied potential and illumination intensity, has been analyzed on the basis of a kinetic model previously proposed. In a basic medium, the model assumes as a first step the photogeneration of surface‐bound radicals from Ti coordinated OH− ions of basic character. radicals further recombine on the surface at a second step, leading to the formation of surface peroxo complexes (chemisorbed species). Finally, photogenerated hydrogen peroxide species become photo‐oxidized and evolves. At small bandbending the decay time constant, τ, characterizing the photocurrent transients is very sensitive to the applied potential, but does not depend on the illumination intensity. The photocurrent‐time dependence is dominated by surface recombination, mainly via photogenerated radicals. The pseudo first‐order rate constant of this reaction shows a gaussian distribution around a main value, with , and representing the bulk electron density and the bandbending respectively. This behavior indicates the existence of a heterogeneous distribution of Ti‒OH− surface sites mediating the process. In the high bandbending region τ is not sensitive to the applied external bias, but strongly depends on the light intensity. The transient is then due to the surface accumulation of positive charge at photogenerated radicals, which produces a slow bandbending decrease and a concomitant diminution of the photocurrent. These effects are controlled by the rate, , of hydrogen peroxide formation, which is a second‐order reaction in the surface concentration of photogenerated radicals. A can be estimated.

The effect of local pH changes and surface hole accumulation on the photocurrent transients observed during water photoelectrolysis at TiO2 electrodes has been studied. The diffusion of pH-determining electrolyte species is found to affect not only the time-dependent photocurrent decay but also the photocurrent vs. potential dependence. Whereas the instantaneous initial photocurrent follows the theoretically expected dependence on the band-bending, the stationary photocurrent deviates from the predicted behaviour, depending on the electrolyte pH. With the help of the rotating disk electrode technique, the ratio between the stationary and the initial photocurrent was studied as a function of the rotation rate, at both pH 10.5 and 12. Variations of band bending, associated with Vfb shifts due to local pH changes, are invoked to explain the observed behaviour. At sufficiently high and low pH values, where photocurrents are not limited by the diffusion of OH− and H+ electrolyte species, the transients are due exclusively to Vfb shifts associated with accumulation of photogenerated holes at the semiconductor surface. These results are consistent with those obtained recently in our laboratory from electrolyte electroreflectance experiments, which allowed for the first time direct measurement of the Vfb shifts occurring during photoelectrochemical water splitting.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComments on "Behavior of surface peroxo species in the photoreactions at titania"P. Salvador and D. TafallaCite this: J. Phys. Chem. 1988, 92, 7, 2075–2076Publication Date (Print):April 1, 1988Publication History Published online1 May 2002Published inissue 1 April 1988https://pubs.acs.org/doi/10.1021/j100318a074https://doi.org/10.1021/j100318a074research-articleACS PublicationsRequest reuse permissionsArticle Views64Altmetric-Citations4LEARN 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 InRedditEmail Other access options Get e-Alerts

Electrolyte electroreflectance (EER) is shown to be an interesting tool for the rapid and reliable measurement of the semiconductor flat-band potential (Vfb). The method proposed consists of sweeping the applied dc potential while measuring the EER signal (ΔR/R) with the help of a phase sensitive amplifier, for constant amplitude and frequency of the applied ac perturbation, and for photons of energy around that of the most probable direct transition of the semiconductor. The applicability of the method is illustrated with Vfb measurements of polycrystalline and single crystal electrodes. The results are compared with those obtained from impedance measurements.

It is well known that stable and efficient liquid‐junction photovoltaic solar cells based on photoanodes can be obtained by coating the semiconductor surface with an indium‐oxide layer and by employing an aqueous polyiodide solution containing Cu+, In3+, and H+ ions. In this work, we further investigated the polycrystalline junction using electrolyte electroreflectance and cyclic voltammetry. The effect of the indium‐oxide overcoat on the semiconductor flatband potential in solutions having different pH values was studied by monitoring the whole specimen surface and small surface areas. Indium is found to be preferentially electrodeposited at surface defects and at zones of high electrical conductivity, while insulating areas (low doped crystallites) remain uncovered. This explains the lack of homogeneity of the In‐oxide layer generated by thermal oxidation of the electrodeposited In. The flatband potential of the surface areas covered with indium oxide is reasonably more affected by electrolyte pH changes than that of uncovered zones. Finally, the influence of pH on the electroreduction efficiency of dissolved anions was investigated on both etched and In‐oxide covered electrodes by cyclic voltammetry. The experimental fact that at acidic media, the electroreduction kinetics of anions is enhanced is consistent with the observed pH dependence of the flatband potential and explains the photostabilizing effect of indium‐oxide overcoating in H+ containing electrolytes.

AbstractSystematic electrolyte electroreflectance measurements of the flatband potential (VFB) are performed on etched and In‐oxide coated polycrystalline n‐CuInSe2 electrodes in contact with a polyiodide electrolyte at different pH values.

AbstractThe experimental setup that allows to observe in situ the overall semiconductor surface and to perform electroreflectance (EER) and photoelectrochemical measurements is described.

On montre que les mesures de l'electroabsorption de l'electrolyte sur une electrode en semi-conducteur peuvent donner des informations sur la bande interdite, sur la tension de bande plate, etc. Cas d'une electrode en verre recouvert de SnO 2 , lui-meme recouvert d'un film semitransparent de CdSe

Thin polycrystalline CdS films were prepared for photoelectrochemical applications. The presence of electronic states in the band gap of the material was investigated by means of several optical techniques. The sub-band-gap photo-current, the photoluminescence and the electrolyte electroluminescence indicated a high density of such states which were attributed mainly to sulphur and cadmium vacancies.

The relationship between crystal structure, photoluminescence spectrum, and photoelectrochemical behavior of CdSexTe1−x alloy layers has been investigated. Layers having the hexagonal wurzite structure are strongly luminescent both in the red (at a photon energy corresponding to the direct bandgap of the alloy) and in the near infrared. Much weaker luminescence is shown by the layers with cubic zincblende structure. Annealing is responsible for recrystallization and cubic-to-hexagonal phase transformation (CdSe-rich alloys), being beneficial to the efficiency both of photoluminescence and of photoelectrochemical solar energy conversion.

AbstractObwohl H2O2 reales Zwischenprodukt bei der H2O‐Photoelektrolyse an n‐TiO2‐Ober?ä‐ chen ist, kann es auch bei unterschiedlichen Arbeitsbedingungen nicht an der ′ rotierenden Ring‐Scheiben‐Elektrode (RRDE) nachgewiesen werden.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe generation of hydrogen peroxide during water photoelectrolysis at n-titanium dioxideP. Salvador and F. DeckerCite this: J. Phys. Chem. 1984, 88, 25, 6116–6120Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://pubs.acs.org/doi/10.1021/j150669a013https://doi.org/10.1021/j150669a013research-articleACS PublicationsRequest reuse permissionsArticle Views421Altmetric-Citations57LEARN 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 InRedditEmail Other access options Get e-Alerts