open access

https://hdl.handle.net/2115/42803

The Photoelectrochemical Production of Hydrogen

英語

1976-10

10, vi, 267p.

A Thesis Presented for the Degree of Doctor of Philosophy in The Flinders University of South Australia

The photoeffects on the oxygen and hydrogen evolution reactions at n- and p-type semiconductors, respectively, have been studied theoretically and experimentally in connection with the direct production of hydrogen from solar energy. The experimental techniques involved in this work include: 1. Photocurrent measurements under the illumination of a 150W or a 900 W Xe lamp, using potential sweep methods. 2. Photo current measurements under illumination by monochromatic light using a Jarrell-Ash grating monochrometer and a Xe lamp. 3. Impedance measurements, using the direct method. 4. Transient photo current measurements following light illumination and light interruption. 5. Chemical vapor deposition to make TiO2 films on other semiconductors. 6. Sintering method for metal titanates synthesis. The following novel experimental matter has been resolved: 1. The quantum efficiency of photoelectrochemical reactions involving hydrogen or oxygen evolution at several potentials and wavelengths involving TiO2, Fe2TiO5, ZnTe, CdTe, GaAs, InP, GaP, SiC and Si in alkaline and acid solution. 2. The flat band potentials of ZnTe, CdTe and SiC in alkaline and acid solution and of InP in alkaline solution at various frequencies. 3. The break down of the photoelectrodes, i.e., TiO2, Fe2TiO5, ZnTe, CdTe, GaAs, InP, GaAs, SiC and Si in alkaline solution and acid solution, as a function of time. 4. The transient behaviour of photocurrents. 5. The prevention of the anodic dissolution of CdS by the use of thin film coating transparent to light. 6. The finding of Fe2TiO5 as a stable photoanode and of CdTe as a stable photocathode. The theory of photoelectrochemical system has been developed originally in the following way. Gurney's quantum mechanical theory of charge transfer reaction was modified to account for the photoelectrochemical charge transfer reaction. The number of electrons arriving at the electrode surface per unit time per unit area at certain energy level was calculated by considering the properties of the semiconductor. The energy levels of an acceptor and a donor states in the OHP were estimated. The potential drop was at first considered to occur totally within the semiconductor. Following this model, photocurrents were calculated and compared with the experimental results. Considerable discrepancies existed between calculated and experimental results. Energy losses of excited electrons within the semiconductor and the potential drop in the electric double layer were then taken into account. Also, the potential barrier for emitted electrons was modified by considering the image interaction of the emitting electron with the semiconductor electrode. The photocurrents calculated by this modified theory agreed fairly well with the experimental results. By applying this theory, the critical potential, at which the quantum efficiency becomes significant, has been related to the flat band potential and the energy gap.

Ph.D.

学術雑誌論文

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