A photoelectrochemical investigation of bismuth sulphide films

by Roxburgh, Ulrich

Abstract (Summary)
Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. This thesis investigates the electrochemical and photoelectrochemical kinetics of bismuth sulphide films. Bismuth sulphide is a semiconductor, with a bandgap of 1.3 eV. making it nearly optimal for conversion of solar energy to electrical energy, but solar cells constructed using bismuth sulphide films have achieved only poor conversion efficiencies. The bismuth sulphide films employed were formed by anodic polarisation of a bismuth electrode in a sulphide medium. A solar cell was fabricated using an anodic bismuth sulphide film; this produced relatively small photocurrents, due to the high resistance of the cell (3010 ?), and the relatively low photovoltage of 68 mV. The formation of anodic bismuth sulphide films was studied, and was shown to proceed initially via growth of a monolayer, under simple chemisorption kinetics, with the rate proportional to the uncovered surface area (1 - ?). This monolayer growth corresponds to the first small anodic peak in the cyclic voltammogram. Coulometry showed that the charge contained in peak A1 (4.5 mC/cm2) was sufficient for about 10 layers of bismuth sulphide, while the electrode roughness factor was found to be close to 10. This confirmed that peak A1 was due to monolayer formation. The bismuth / polysulphide system was also studied using AC impedance, leading to an equivalent circuit model consisting of a resistance in series with a parallel resistance – capacitance combination, which gave a good fit over the frequency range measured. Due to the poor conversion efficiency of the anodic bismuth sulphide film, formation of bismuth sulphide films by cathodic deposition was investigated. The approach was to reduce a sulphur species to sulphide in the presence of bismuth(III). These experiments were carried out in non-aqueous solvents, since bismuth ions are readily hydrolysed in aqueous solutions. The system investigated was NaSCN in acetone, with BiCl3 as the Bi(III) species. Attempts to form bismuth sulphide films on an iron electrode were unsuccessful however, because the reduction of Bi(III) was more facile than the reduction of SCN- in the acetone medium. Despite the lack of success in forming bismuth sulphide by cathodic deposition, the kinetics of iron and bismuth electrodes in the acetone medium were investigated further. The reduction of Bi(III) appears to be under activation control, and is more facile on iron than on bismuth. The reduction of SCN- seems to be irreversible, and the reduction potential is dependent on pH and concentration. The kinetics of a Bi electrode in the acetone medium were also studied.
Bibliographical Information:


School:The University of Auckland / Te Whare Wananga o Tamaki Makaurau

School Location:New Zealand

Source Type:Master's Thesis



Date of Publication:01/01/1988

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