ELECTROCHEMICAL-BEHAVIOR, RAMAN CHARACTERIZATION, AND PHOTOELECTROCHEMISTRY OF CUPROUS THIOCYANATE-POLYPYRROLE BILAYERS AND FILMS

This study describes new types of bilayers or electrode surfaces which combine an organic semiconductor (polypyrrole, PPy) and an inorganic counterpart (cuprous thiocyanate, CuSCN). Two bilayer structures, namely, Cu/CuSCN/PPy and GC/PPy/CuSCN, were compared using voltammetry and in situ Raman spectroelectrochemistry techniques. Aqueous media containing pyrrole and KSCN were found to be unsuitable for growing thick and adherent layers of polypyrrole either at copper or at platinum support electrodes. On the other hand, tetrahydrofuran solutions containing pyrrole and a supporting electrolyte were effective for electrosynthesis of the Cu/PPy system. The latter was modified into a Cu/CuSCN/PPy bilayer by electrochemical reaction with thiocyanate ions. This system showed interesting photoelectrochemical transients arising from the unidirectional flow of minority carriers (electrons) from p-CuSCN to polypyrrole. The transients are contrasted with those observed under chopped white light irradiation of the Cu/CuSCN/electrolyte interphase, wherein a trap-dominated photoresponse was seen. The GC/PPy/CuSCN bilayer showed high ohmic resistance and barrier to CuSCN film formation, presumably because charge transport in this system has to be mediated by an underlying (resistive) PPy layer.