Photoelectrolysis using chlorophyll electrodes.

Abstract

By the conversion of sunlight to chemical energy, photoelectrolysis was carried out using two different chlorophyll-redox compound lining electrodes. These electrodes were prepared by covering platinum plates with chlorophyll and naphthoquinone or anthrahydroquinone and a conducting adhesive. These electrodes exhibit a photoexciting property. The potential was found to shift to a less noble state when the system of the chlorophyll-naphthoquinone electrode was inserted into NAD solution with illumination. On the other hand, the photoexcitation of the system of the chlorophyll-anthrahydroquinone electrode inserted into ferrocyanide solution made the potential more noble. (If the potential in the dark is in the dark is in the positive region of the scheme and the potential moves in the positive direction when the light is turned on, it can be said to be more positive region, it can be said to become less noble, but it is not suitable to say that it becomes more negative.) To make the potential difference between two electodes as big as possible, various factors such as intensity of illumination, molar ratio of chlorophyll to naphthoquinone or anthrahydroquinone and concentration of redox compound in electrolyte were examined. A cell was set up by combining the system of the chlorophyll-naphthoquinone electrode in NAD solution with that of the chlorophyll-anthrahydroquinone electode in ferrocyanide solution, and photoelectrolysis was carried out by closing the external circuit with illumination. The photovoltage between the two electrodes was 0.25 V and the current density was 8 muA/cm2. It was found that NAD was reduced to form NADH at the chlorophyll-naphthoquinone electrode and ferrocyanide was oxidized to form ferricyanide at the chlorophyll-anthrahydroquinone electrode.