Generation of Light-Induced Electrical Potential from Ion Exchange Membranes Containing 4 , 4 ′ -Bipyridine Moiety: IV. Effect of Presence of n-Type Semiconductors in a Photocell on Electrical Potential

Abstract

Anion exchange membranes with viologen moiety containing fine particles of anatase- were prepared by the casting method and photovoltage generation was examined by photoirradiation to one surface of the membrane after assembling the photocell [clamping the membrane swollen with ethylene glycol between two indium-tin oxide (ITO) electrodes]. Higher photovoltage (175 mV, load resistance, 200 k Ω) rapidly generated compared with the membrane without (105.7 mV). However, the photovoltage was anisotropic concerning the direction of the membrane surfaces due to heterogeneous distribution of the particles across the membrane. Thus, the photocell was examined by assembling the cell composed of the anion exchange membrane with a viologen moiety (without swollen with ethylene glycol or triethylene glycol and an n-type semiconductor (CdS, rutile- and anatase- layer. A photovoltage of more than 350 mV was observed by photoirradiation to the semiconductor layer side. This was due mainly to electrons generated from excited n-type semiconductor, which were collected at the ITO electrode, and due to reduction of the viologen moiety of the membrane at the dark side by the electrons via a load resistance. The formed hole on the semiconductor is thought to migrate through the membrane to the dark side via the solvent by a hopping mechanism and then oxidize reduced viologen moiety at the dark side. A thicker layer rapidly generated higher photovoltage (the highest photovoltage, 617 mV). Electrons from exited significantly contributed to the photovoltage compared with electrons released from the viologen moiety. © 2003 The Electrochemical Society. All rights reserved.