Semiconductor electrodes. 13. Characterization and behavior of n-type zinc oxide, cadmium sulfide, and gallium phosphide electrodes in acetonitrile solutions

Abstract

The photoelectrochemical behavior of n-ZnO, -CdS, and -GaP single crystal semiconductor electrodes was investigated in acetonitrile which contained various electroactive compounds whose standard redox potential varied by over 3.2 V.The cyclic voltammograms of the n-type semiconductors in the dark and illuminated were compared to the Nernstian behavior at a Pt disk electrode. The photodissolution of the semiconductor electrodes did not occur until the electrode potential was well positive of the flat band potential. An underpotential was developed for the photooxidation of solution species at each semiconductor. A model for electron transfer at the semiconductor-solution interface is proposed which incorporates a surface state or intermediate level which can mediate electron transfer and surface recombination. The model is used to discuss previous work with semiconductors, electron transfer, and stabilization of the semiconductor surface.Key factors in the utilization of semiconductor electrodes in electrochemical cells and devices, including those for solar energy conversion, are knowledge of the relative locations of the energy levels in the semiconductor and solution and an understanding of the role that surface states or intermediate

Modes of Charge Transfer at an Illuminated Semiconductor Electrode, a Digital Simulation

“…Thus it may be predicted that a defective surface (i.e., polycrystalline SC) can be beneficial in the preventing of the anodic photodissolution of low bandgap semiconductors (the slow hole injection process) (15). Such a "shielding" effect was recently found experimentally: The long-term stability of a polycrystalline film of CdSe was found to be superior to that of a single crystal material although the initial photocurrent of the latter is higher (18).…”

Field Effect Modulation of Outer-Sphere Electrochemistry at Back-Gated, Ultrathin ZnO Electrodes

“…For the case of TBBQ voltammetry, it is crucial to note that the formal potential E o lies below the CB edge (~0.7 V vs. Fc 0/+ ) for ZnO 26 (i.e., it lies in the band gap), as shown schematically in Figure 1c. The key result of our paper is thus shown in Figure 2a, which displays the CV for TBBQ at the 5 nm ZnO electrode as a function of back gate voltage (V BG relative to a grounded contact on the ZnO, Figure 1a).…”

Reaction of hydroquinone with hematite

“…Kohl and Bard observed a separation of oxidation and reduction peaks ( E p ) of 3.7 V (!) for hydroquinone on n-GaP [38]. In this case the oxidation reaction peak center was at a potential close to the conduction band edge and the reduction peak center at a much more negative potential.…”

“…In this case the oxidation reaction peak center was at a potential close to the conduction band edge and the reduction peak center at a much more negative potential. If such were the case for hematite we would not expect to see the reduction peak due to decomposition of the solvent (Kohl and Bard [38] worked in acetonitrile to avoid this problem). Fig.…”