ELECTROCHEMICAL QUARTZ CRYSTAL MICROBALANCE MONITORING OF CADMIUM-SULFIDE GENERATION IN POLYPYRROLE AND POLYPYRROLE POLY(STYRENESULFONATE) THIN-FILMS

Cadmium sulfide, CdS, particles have been in situ generated electrochemically in polypyrrole, PPy, and polypyrrole-poly(styrenesulfonate), PPy/PSS-, composite thin films on a gold-coated quartz crystal electrode. Two different approaches have been taken. In the first approach, cadmium ions have been attached to the PPy/PSS- composite thin film, formed upon subjecting an aqueous deoxygenated 2.0 x 10(-2) M pyrrole solution to an E = 0 to E = 600 mV potential step in the presence of 1.0 x 10(-3) M PSS- and 0.10 M NaCl. Addition of cadmium ions followed by the introduction of bisulfide ions (HS-) has led to the formation of CdS particles at a number of nucleation sites. In the second approach, HS- ions have been electrochemically oxidized to elementary sulfur in the matrices of PPy thin films, formed upon applying a potential step from E = 0 to E = 650 mV to an aqueous deoxygenated 2.0 X 10(-2) M pyrrole solution in the presence of a 0.10 M NaCl supporting electrolyte. Subsequent to the removal of excess HS- (by ion exchange by CI-) cadmium ions have been added to the solution bathing the PPy-coated electrode. Cathodization has then reduced both the oxidized form of PPy and the elementary sulfur and has led to the formation of CdS particles at a large number of nucleation sites. Interfacial mass changes which have accompanied the formation of PPy and PPy/PSS- thin films and CdS formation therein have been monitored by an electrochemical quartz crystal microbalance. Scanning electron microscopy and X-ray diffraction measurements have confirmed the presence of nonuniform CdS particles in the PPy and PPy/PSS- films.