Anodized cuprous oxide photocathodes for solar energy conversion

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Copyright: Wang, Peng
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Abstract
In this thesis, Cu2O-based composite thin films with high visible light photoactivity were synthesized by electrochemical anodization and electrodeposition methods. Their photoelectrochemical (PEC) activity and stability for solar energy conversion applications especially PEC water splitting were studied. Firstly, Cu2O thin films were fabricated by anodization of Cu foil in fluoride-based organic electrolyte. The growth of CuO nanowires embedded within Cu2O matrix was initiated by thermal treatment, and was found to be effective to enhance the adhesion of oxide layers to Cu substrate, as well as stabilizing Cu2O layer by passivating its redox activities. In the second part, a thin TiO2 layer was introduced between Cu2O and CuO layers to fabricate visible-light-induced highly stable Cu2O-TiO2-CuO heterojunction photocathodes. Cu2O semiconductor with a narrow band gap served as a visible light absorber, while TiO2 semiconductor with a wide band gap was used as an electron transfer shuttle between Cu2O and CuO as well as a stabilizer to improve the stability of the photoelectrode. The good coverage and close proximity of TiO2 protective layer to the Cu2O layer significantly suppressed redox activities of Cu2O at the semiconductor-electrolyte interface. Due to the well-matched band energy alignment between these tri-components, TiO2 layer facilitated electron transfer from Cu2O to CuO, suppressing the recombination of electrons and holes. Accordingly, improvement of both PEC stability and photoactivity of the photoelectrodes were observed. The third part of this thesis demonstrates the modification of intrinsic electronic structure of Cu-Cu2O-CuO composite photoelectrodes by preservation of Cu and introduction of nitrogen using urea treatment. Consequently, the urea-treated photoelectrodes illustrated enhancement of carrier density by five orders of magnitude, reduction of resistivity and acceleration of electron transfer. In the last part of this work, n-type Cu2O thin films over fluorine doped tin oxide (FTO) glass were fabricated by electrodeposition approach in copper acetate-based solution. The conductivity type of the electrodeposited Cu2O thin films can be tuned from n-type to p-type by simple thermal treatment, showing great potentials in fabrication of bias-free tandem type photoelectrochemical water splitting system made of p- and n-type Cu2O photoelectrodes.
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Author(s)
Wang, Peng
Supervisor(s)
Amal, Rose
Ng, Yun Hau
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Publication Year
2015
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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