Date

May 1988

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Materials Science and Engineering

Institution

Oregon Graduate Center

Abstract

Well characterized and reproducible semiconducting Fe2O3 was prepared by freeze-drying. This technique produced very homogeneously Si, Mg, or Pt doped semiconducting Fe2O3 that was used successfully in the photoelectrochemical and photocatalytic solar cell for the production of gaseous hydrogen and oxygen by dissociating water. Photocurrents obtained with the photoelectrodes prepared from the freeze-dried samples were more stable and up to ten times higher than with the samples prepared by the conventional solid state mixing technique. The maximum photocurrent density obtained with the freeze-dried samples was 10 mA/cm2 at 0.8 V vs SCE for the 0.1 at.% Si + 5 at.% Pt doped Fe2O3. The photocurrent also increased with increasing amounts of platinum. The added platinum was shown to have several beneficial effects on the n-type and p-type photoelectrodes. In the Si doped n-type semiconductor the platinum increased the carrier concentration via a shallow donor level within the bandgap. It was also shown that the platinum enhanced the probabilities of electron exchange and increased the reaction kinetics between the electrode and electrolyte species. The efficiency of the photoelectrochemical reactions was increased with added platinum by eliminating the transient currents. In the cyclic voltammetry experiments it was shown that the platinum in the n-type semiconductor at negative potentials acts as a local cathode and enhances the production of hydrogen. In the p-type Fe2O3, the platinum acts as an electrocatalyst and lowers the overpotential for hydrogen reduction. A p/n heterojunction was used in the photoelectrochemical solar cell to photodissociate water into oxygen and hydrogen with visible light. This important result was further improved by using Fe2O3 electrodes prepared by freeze-drying and by the addition of platinum. The photogeneration of oxygen was also achieved in the photocatalytic solar cell by irradiating doped and platinized Fe2O3 in the presence of an electron scavenger. The Fe2O3 was found to be stable against photocorrosion for extended periods of illumination and photocurrent generation in a basic electrolyte. It was shown that doped and platinized freeze-dried Fe2O3 can be used more efficiently than the Fe2O3 prepared by the solid state technique in the photoelectrochemical and photocatalytic cell for the gaseous fuel generation using solar energy.

Identifier

doi:10.6083/M4W093VR

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