A One-Volt p-lnP/n-CdSe Regenerative Photoelectrochemical Cell

Photoelectrochemical (PEC) cells have the potential utility of being used for either the direct conversion of solar energy to electri-city as in regenerative devices or to generate stored redox species which can later be electro-chemically discharged in a suitable cell. This latter approach has been particularly intrigu-ing to us over the last few years. However, although several photoelectrochemical storage cells have been discussed by ourselves and others (1-5), it has become increasingly desir-able to have a high-voltage (=I V) PEC cell, so that the storage cell with which it is asso-ciated has some hope of being competitive with presently available commercial batteries. One approach whereby liquid-junction pho-toelectrochemical cells might be used as an electrical energy storage device is to identify regenerative systems possessing sufficient photopotential for the direct charge of an ex situ electrochemical storage cell, where a bi-polar electrode configuration between the PEC and the electrochemical cell might be feasible. The use of this type of cell configuration, shown schematically in Figure I, could lead to a considerable simplification in the interfac-ing between PEC solar cells and the ex situ--. _ _ electrochemical storage device. Such an ap-proach would have merit if the ex situ stored redox couple has a sufficiently high voltage (i.e.>0.5 V) so that in spite of the inevit-able overpotential losses, electrochemical energy efficiencies of ~75 % might be achievable for the discharge reaction at practical current densities. An incidental benefit might be in achieving some degree of thermal management within the cell due to the circulation of the storage redox electrolytes. The incentive to identify such a regenera-tive cell came from our earlier work with pho-toelectrochemical storage cells, one of the most recently discussed (5) having the over-al