Semiconductor Electrodes: XXV . The System. Photoelectrochemical Cells and Photoelectrochromic Displays

Abstract

The photoreduction of aqueous solutions of 1,1'‐diheptyl‐4,4'‐bipyridyl (heptyl viologen, HV2+) bromide on was investigated. Under irradiation with light of wavelengths below 885 nm, the photoreduction of HV2+ to form a precipitate of violet occurs on at a potential of ∼400 mV more positive than the reversible potential of the couple on Pt. Oxidation of back to soluble HV2+ occurs in the dark at more negative potentials. Photoelectrochemical low capacity storage cells based on this reaction with Cu, Ni, or counterelectrodes were constructed. In such cells, under illumination, the electrode behaves as the cathode, a photovoltage develops, and current flows in the external circuit, while precipitates on the electrode surface, and the counterelectrode is oxidized. In the dark, the current flows in the opposite direction, the is the anode, and reduction occurs at the counterelectrode. 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.