Semiconductor Electrodes 25. The p-GaAs/Heptyl Viologen System. Photoelectrochemical Cells and Photelectrochromic Displays

摘要

The photoreduction of aqueous solutions of 1,1'-diheptyl-4,4'-bipyridyl (heptyl viologen, HV(2+)) bromide on p-GaAs was investigated. Under irradiation with light of wavelengths below 885 nm, the photoreduction of HV(2+) to form a precipitate of violet HVBr occurs on p-GaAs at a potential of approx 400 mV more positive than the reversible potential of the HV(2+)/HVBr couple on Pt. Oxidation of HVBr back to soluble HV(2+) occurs in the dark at more negative potentials. Photoelectrochemical low capacity storage cells based on this reaction with Cu, Ni, or HxNb2O5 counter electrodes were constructed. In such cells, under illumination, the p-GaAs electrode behaves as the cathode, a photovoltage develops and current flows in the external circuit, while HVBr precipitates on the electrode surface and the counter electrode is oxidized. In the dark, the current flows in the opposite direction, the p-GaAs is the anode and reduction occurs at the counter electrode. Such a cell also produces an alternating electrical output under periodic illumination. Photoelectrochromic cells based on this reaction and utilizing simultaneous addressing with light and electrical signals are also proposed. (Author)