Electrochemical Properties of Nanocrystalline Cadmium Stannate Films

Abstract

Electrochemical properties of sol-gel nanocrystalline cadmium tin oxide electrodes (CTO) were investigated in 0.2 M potassium chloride buffered at pH 7.4 with phosphate. Films were found to be n-type degenerate semiconductors with charge carrier levels from to depending on the thermal aftertreatment. X-ray diffraction analysis was used to reveal the appearance of the cubic cadmium stannate phase at annealing temperatures above 600°C, and to indicate the extent of this dominant phase above 750°C. The flatband potential of the film electrodes, as determined from capacitance measurements, was found to be around +0.25 V at pH 7.4. Electrochemical activity toward ten redox processes in the range V was investigated, and standard electron transfer rate constants were estimated from ac impedance measurements. The dominant factor in the charge-transfer rate on CTO electrodes is the bulk film charge carrier concentration. It was found that the charge-transfer rates were dependent on the separation of the redox carrier formal potential from the CTO flatband potential. The slowest rates cm were found for redox couples where For charge transfer from redox couples where is away from the rates can be several orders of magnitude greater and it is thought that the density of states in the conduction band is rate limiting. © 2001 The Electrochemical Society. All rights reserved.