Photochargeable multilayer membrane device composed of CdS film and prussian blue battery

Abstract

Photoenergy conversion and storage are attracting attention not only in solar energy utilization but also in photodevices which are important for the future socalled photonics (photoelectronics). Photoinduced charge separation and the following accumulation of the separated charges are typical processes in photoenergy/information conversion and storage. These processes are generally carried out in different systems or phases respectively to result in a whole achievement. If they are combined to realize in one device, it must be of much value for the development of photodevices. Such a device is capable of photocharge and dark-discharge, and would open a new field in photoenergy and information conversion/storage. Some systems for photocharge and dark-discharge have been reported that are composed of liquidjunction semiconductor and redox electrolyte present in solution[l-51. A new concept is now proposed to realize photocharge and dark-discharge by a multifunctional solid state device, which must be of great use for practical application. The present authors have designed a multilayer membrane device for photocharge and dark-discharge so that each layer bears a function such as photoinduced charge separation, accumulation of positive/negative charges, separation of reactants. As for the membrane materials, polymer is most suited for practical use[6]. As a charge storage material, Prussian Blue (PB) which is a high molecular and polynuclear mixedvalent iron cyanide complex was chosen in the present paper. Electrochemical behavior of PB has been well characterized by Neff and Itaya et aI.[7-91. This complex, whose composition is represented by Fe:’ [Fe”(CN),]:-, has three kinds of reversible redox states, so that it can store both positive and negative charges. PB batteries were reported by NefllO], Kanekorll, 123, and Honda et al.[13] in which two PB films were utilized for an anode and a cathode. A multilayer PB polymer battery (PB/Nafion/PB) has been fabricated, and its reaction characteristics have been studied electrochemically and spectrophotometrically by the present authors[12]. Photoreaction of PB film coated on TiO, has been studied in aqueous electrolyte solution[14], but this system uses only ultraviolet light and dark-discharge has not been reported. In the present paper, a multilayer solid type photochargeable device driven by visible light irradiation will be reported which is composed of n-CdS semiconductor film and trilayered PB battery membranes.