Electrochemical and Photoelectrochemical Properties of the Semiconducting SrTiO₃ Single Crystal Electrode

Abstract

F. Vanden Kerchove et al.: Electrochemical and Photoelectrochemical Properties etc sponding to a kinetic energy spread of 0 to 27.2kJ/mol. Practically no kinetic cooling will result from collisions with Nz and 02, since these molecules are extremely efficient quenchers of O('D). However, the presence of a minor constituent in excess of the stratospheric N,O mixing ratio of less than 0.3 ppm would sufiice to reduce the average kinetic energy of those O('D) atoms which react with NzO, provided that the quenching efficiency of the minor constituent is much less than unity. This condition is met by the noble gases [ 163, and by Argon in particular. -Anyway, to obtain the yield of NO molecules per N 2 0 reacting with O('D) in the stratosphere, b = kzb/k2 has to be known for kinetic energies of O('D) below 27.2 kJ/mol. The value b = 0.617 0.015 obtained in this work is independent of kinetic energy in the range of interest, and corresponds to a yield of 1.23 NO molecules for each NzO molecule consumed by O('D). This is 23% higher than the yield of 1.00 which is widely used in model calculations. The recent results of Schiff [15] as well as Pirkle et al. [I41 fall between these limits. Elektrochemie 1 Hulbleiter 1 Oberfliichenerscheinungen 1 Phoroelektrochemie / StromverdoppelungThe photoelectrochemical behaviour of several reagents at the Sr'TiO, anode has been investigated. Current-doubling was found with several reducing agents. By competitive reaction experiments, hole capture was detected with some other reagents. Quantitative data on relative hole reactivities were obtained for several reducing agents, including water. The position of the band edges at the semiconductor surface was deduced from capacitance measurements. The reactivity data are interpreted in terms of the position of electron energy levels at both sides of the surface, and the applicability of the direct electron transfer model to the reactions observed is discussed. Untersucht wurde das photoelektrochemische Verhalten verschiedener Reagenzien an der SrTi0,-Anode. Bei verschiedenen reduzierenden Zusatzen wurde Stromverdoppelung gefunden. Aus einer Untersuchung von Konkurrenzreaktionen wurde bei einigen anderen Reagenzien Defektelektronenfang festgestellt. Quantitative Ergebnisse in bezug auf relative Defektelektronenreaktivitaten wurden fur verschiedene Reagenzien, einschlieBlich Wasser, erzielt. Die energetische Lage der Bandkanten an der Halbleiteroberflache wurde aus Kapazitatsmessungen abgeleitet. Die Reaktivitatsergebnisse wurden aufgrund der energetischen Lage der Elektronenniveaus an beiden Seiten der Phasengrenze interpretiert, und die Anwendbarkeit des direkten Elektronenubergangsmodells auf die beobachteten Reaktionen wird besprochen. Absorptionsspektren, von Kristallen Elektrochemie I Halbleiter / Oberjlachenerscheinungen 1 PhotoelektrochemieA comparative study was made on the photocurrent of etched and mechanically polished n-GaAs single crystal electrodes. The photocurrent was investigated as a function of voltage, light intensity a...

The Photoelectrochemical Kinetics of p‐Type GaP

“…In this region of potential the photocurrent is insensitive to the concentration of Fe(III). From these results we draw the important conclusion that there is no current doubling (19,20) in the production of H2 at GaP. Both electrons involved in the production of H2 must be photogenerated electrons from the conduction band.…”

Electrochemical Production of Hydroxyl Radical at Polycrystalline Nb-Doped TiO2 Electrodes and Estimation of the Partitioning between Hydroxyl Radical and Direct Hole Oxidation Pathways

“…product of formate is unstable and immediately injects another electron into the electrode (a process called "current doubling"). 28,29 Since formate was shown to undergo a twoelectron oxidation in our experiments as well, the current increase data were analyzed assuming that two electrons were transferred for each molecule of formate that was consumed from the solution.…”

Kinetic Investigation on the Mechanism of the Photoelectrochemical Oxidation of Water and of Competing Hole Processes at the TiO2 ( Rutile ) Semiconductor Electrode

“…Indeed, when cs ~ 0 and c is kept constant, IBr is a function of the rotation speed only (see Eq. [2] and [3]). A value of D = 1.56 • 10 -9 mS-s -' was obtained in 0.33 mol-dm -~ HCIO4 as the supporting electrolyte, which is in good agreement with that measured by Johnson and Bruckenstein (13) in i tool-din -3 H2SO4 (D = 1.58 • 10 -9 m2_s-I).…”

“…Under circumstances of diffusion control, Cs is smaller than the bromide concentration in the bulk, c. In the steady state, the flux of material reacting at the electrode surface must equal the flux being transported through the diffusion layer. Hence Iog(i/t.l.A.cm -2) X D : 0.643 W -'~ v ' 16 D "3 [3] with W the rotation speed of the RRDE (in revolutions per second) and v the kinematic viscosity of the solution (v = 0.9 x 10 -6 m~-s-').…”

“…Therefore, data on the reactivity of water for holes and on the different steps of this oxidation are not directly accessible by kinetics, and can only be obtained by studying the competition between different reagents for the holes at the electrode surface. One possible method, which was formerly used for TiO~ (2) and SrTiO~ (3), consists of the measurement of the photocurrent under the addition of so-called current doubling reagents to the photoelectrochemical cell. A more recent technique uses the rotating ring-disk electrode (RRDE): the reaction product of one of the competitive photoreactions at the semiconductor disk electrode is detected specifically at the metal ring electrode.…”