Electrochemical Properties of Nanocrystalline Cadmium Stannate Films

Published

August 1, 2001

Author(s)

Gintaras Valincius, Vytas Reipa, V L. Vilker, John T. Woodward IV, Mark D. Vaudin

Abstract

Electrochemical properties of the 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 10¹⁹ to 10²² cm^-3 depending on the thermal aftertreatment. X-ray diffraction analysis was used to reveal the appearance of the cubic cadmium stannate (Cd₂SnO₄) phase at annealing temperatures above 600 C, and to indicate the extent of this dominant phase above 750 C. The flatband potential (E_FB,) of the film electrodes, as determined from capactiance meaasurements, was found to be around +0.25 V at pH 7.4. Electrochemical activity toward ten redox processes in the range 0.45 V < E < 0.45 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 (E⁰¹) from the CTO flatband potential. The slowest rates (nearly equal to}10^-5 cm s^-1) were found for redox couples where E⁰¹ nearly equal to} E_FB. For charge transfer from redox couples where E⁰¹ is away from E_FB, 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.

Citation

Journal of the Electrochemical Society

Volume

148

Issue

No. 8

Pub Type

Journals

Keywords

cadmium stannate, electrode, electron transfer, impedance, metal-oxide, rate constants

Citation

Valincius, G. , Reipa, V. , Vilker, V. , Woodward IV, J. and Vaudin, M. (2001), Electrochemical Properties of Nanocrystalline Cadmium Stannate Films, Journal of the Electrochemical Society (Accessed April 19, 2024)