Electrochemical studies of semiconducting SnO<sub>2</sub>‐electrodes

Möllers, F.; Memming, R.

doi:10.1002/bbpc.19720760603

Cited by 107 publications

(13 citation statements)

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“…The flatband potentials (EFB) Of the SnO2 electrodes in 10-2M H2SO4 varied from sample to sample, but were all near --0.1 to --0.2V vs. SCE. This is, as expected, somewhat negative of EFB values reported for SnO2 with lower charge carrier densities (12), but positive of values recently obtained (13) for highly conducting SnO2 films similar to those used in the present study. Charge carrier densities were mostly in the range 4-7 • 1020 cm -3.…”

Section: Methodssupporting

confidence: 90%

“…Before using the SnO2 electrodes to investigate electrode processes in the iron-thionine cell, several of them were characterized as follows. The fiatband potential and charge carrier density were determined from capacitance vs. potential data, which were used to construct Schottky-Mott plots (1/C a vs. E) (12). The best straight-line fit was obtained by computer.…”

Section: Methodsmentioning

confidence: 99%

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Electrodic Phenomena at the Anode of the Totally Illuminated, Thin Layer Iron‐Thionine Photogalvanic Cell

Hall

Wildes

Lichtin

1978

J. Electrochem. Soc.

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Properties of Corning thin-film SnO2 electrodes in contact with 0.005-0.5M solutions of sulfuric acid in aqueous solvents containing 0-50 v/o CH3CN were characterized. Schottky-Mott plots gave. flatband potentials (EFB) in the range 0-0.2V vs. SCE and charge carrier densities in the range 4-7 • 103~ cm -~ in 0.01M sulfuric acid, independent of solvent composition. Standard reduction potentials vs. SCE in 0.01M acid at room temperature were calculated from equilibrium compositions to be --0.04V for TH+/.TH2 +, 0.33V for -Tt~2+/TH4 ~+ and 0.14V for TH+/TH42+ in water and --0.06V for TH+/-TI-I2 +, 0.28V for .TH2+/TH42+ and 0.11V for TH+/TH42+ in 50 v/v/o aq. CH3CN. Voltammetric data show that establishment of protonic equilibrium is rapid compared with cathodic reduction of TH + at SnO2 in water and in 50 v/o aq. CH3CN. In contrast, protonic equilibration between the two electrontransfer steps is slow for thionine-l-sulfonic acid. Voltammetric data show that reduction of TH + and oxidation of TH42+ are kinetically controlled at both SnO2 and Pt electrodes with reversibility greater at platinum than at SnO2. Reversibility is slightly reduced by addition of CI-I~CN to the solvent. Rectification (inhibition of oxidation of TH4 ~+) is not severe enough to prevent the use of SnO2 as a selective anode but may reduce efficiency of photogalvanic conversion. Weak but persistent adsorption of TH + on SnO2 activates photogalvanic conversion. Adsorption of TH42+ varied considerably from sample to sample of SnO2 and was strong in some cases. Both oxidation and reduction of the Fe+8/Fe +~ couple are much less reversible at SnO2 than at P t. Rectification (inhibition of oxidation of Fe 2+) is pronounced. Both oxidation and reduction on SnO2 become more reversible with increasing fraction of CI-I~CN; the major effect is enhancement of oxid_ation of Fe 2+ but even with 50 v/o CI-IaCN the couple is much less reversible than at Pt. Implications of the data with respect to efficiency of totally illuminated thin-layer ironthionine photogalvanic cells are discussed.A totally illuminated, thin layer iron-thionine photogalvanic cell has been described in recent publications (I-3). It differs from many other photoelectrochemical cells, which are essentially solid-liquid junction photovoltaic cells (4), because light is absorbed by solution species, initiating a photoredox reaction which produces high energy products. The energy conversion process is reversible, in the sense that the electrode reactions reform the photoredox reactants. Thus, the cell can be operated continuously.The photogalvanic cell anode is a large bandgap ntype semiconductor with a high charge carrier density, which is transparent to the excitation radiation. Tin oxide is commonly used (1-3, 5), although highly reduced TiO2 thin films have also proved suitable (6). As discussed in an earlier paper (I), the two photogalvanic cell couples discharge at the semiconductor electrode at widely differing rates. Consequently, under illumination a photopotential is established wit...

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Section: Methodssupporting

confidence: 90%

Section: Methodsmentioning

confidence: 99%

Electrodic Phenomena at the Anode of the Totally Illuminated, Thin Layer Iron‐Thionine Photogalvanic Cell

Hall

Wildes

Lichtin

1978

J. Electrochem. Soc.

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“…[9] RT ~lCT --~ ~J [11] nFjo At larger values of .~], the back reaction, i.e., the second term in the brackets of Eq. [9], becomes negligible and the electrochemical reaction can be described by the well-known Tafel equation (anodic) ~ICT = aTtF These expressions may be introduced into Eq.…”

Section: Rtin ( J--jic )mentioning

confidence: 99%

“…11) by the linearized function Eq. [11]. This is not possible when an "irreversible" reaction, such as the chlorine evolution on SnO2, is considered.…”

Section: Rt(dj)mentioning

confidence: 99%

“…SnO~ is a particularly attractive material for this purpose because of its high transmittance in the visibleinfrared range, its resistance against chemical attack, and because of the possibility of incorporating foreign atoms which modify both solid-state and interracial properties in a wide range (9)(10)(11)(12). We shall consider the following electrodes composed of n-type Si-SnO2 heterojunctions.…”

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The Photocurrent‐Voltage Characteristics of the Heterojunction Combination n ‐ Si / SnO2 / Redox ‐ Electrolyte

Decker

Fracastoro‐Decker

Badawy

et al. 1983

J. Electrochem. Soc.

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A model for Schottky barrier-like heterojunction photoelectrodes is presented. This model allows the calculation of the current-voltage curves for such electrodes under different conditions of illumination and electrochemical charge transfer. SnO2-coated n-type Si electrodes in contact with the redox systems KJK4 Fe (CN)e and C12C1-show experimental photocurrent-voltage curves with the behavior predicted by the model. The effect of the charge transfer overvoltage and the expected current limitation due to photon control and/or redox ion diffusion are demonstrated. The feasibility of solar energy conversion through photoelectrolysis, by means of cells based on heterojunction photoelectrodes, is discussed.Photocorrosion is a general problem of photoelectrochemical cells where small bandgap semiconducting electrodes are used. To avoid this problem, a range of coatings has been applied to the electrode surfaces. Thin layers of metals (1-5) or of transparent and conducting oxides (6-8) have been deposited onto the semiconductor by different techniques. The resulting electrodes can mostly be described as Schottky barrier-like heterojunctions with an electrolyte front contact.SnO~ is a particularly attractive material for this purpose because of its high transmittance in the visibleinfrared range, its resistance against chemical attack, and because of the possibility of incorporating foreign atoms which modify both solid-state and interracial properties in a wide range (9-12). We shall consider the following electrodes composed of n-type Si-SnO2 heterojunctions. A schematic representation of the Si-SnO2-electrolyte system is given in Fig. 1. The photovoltage Vj is generated at the junction SiSnO2, which is a device of the Schottky barrier type (13). The electrochemical reaction, on the other hand, proceeds at the SnO~-electrolyte interface and is thus separated from the photoactive junction by the protective oxide film. This physical separation is advantageous in the definition of the current-voltage characteristics of the system since it permits first analyzing separately and then combining the concepts characterizing the photovoltaic and the electrochemical part of this photoelectrochemical cell.In this work, we derive a mathematical model for the treatment of heterojunction photoelectrodes. Furthermore, we shall use this model to discuss the performance of illuminated Si-SnO~ electrodes in contact with the redox systems I~/K4 Fe(CN)6 and C12/C1-. We disregard in our treatment the special case of such thin layers (< 50A) that can be tunneled by photogenerated minority carriers. Their protection against corrosion is not likely to last for long enough time since it is hardly possible to produce such thin layers without pinholes or larger defects. The SnO2 layers of about 800A thickness used in our experiments here were tight, and we could not detect any photocorrosion of the silicon after more than 30 hr of operation under solar-like illumination (14). TheoryThe equivalent circuit corresponding to the consi~lered photoe...

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Semiconductor Electrochemistry

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Electrochemical studies of semiconducting SnO₂‐electrodes

Cited by 107 publications

References 13 publications

Electrodic Phenomena at the Anode of the Totally Illuminated, Thin Layer Iron‐Thionine Photogalvanic Cell

Electrodic Phenomena at the Anode of the Totally Illuminated, Thin Layer Iron‐Thionine Photogalvanic Cell

The Photocurrent‐Voltage Characteristics of the Heterojunction Combination n ‐ Si / SnO2 / Redox ‐ Electrolyte

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Electrochemical studies of semiconducting SnO2‐electrodes

Cited by 107 publications

References 13 publications

Electrodic Phenomena at the Anode of the Totally Illuminated, Thin Layer Iron‐Thionine Photogalvanic Cell

Electrodic Phenomena at the Anode of the Totally Illuminated, Thin Layer Iron‐Thionine Photogalvanic Cell

The Photocurrent‐Voltage Characteristics of the Heterojunction Combination n ‐ Si / SnO2 / Redox ‐ Electrolyte

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Electrochemical studies of semiconducting SnO₂‐electrodes