Tailoring Electronic Structures of Semiconductor Thin Films for Photoeletrochemical Applications


Student thesis: Doctoral Thesis

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Award date2 Sep 2021


In recent years, the global growth in demand for energy and industrial products has become much higher. However, the serious environmental problems caused by using fossil energy have also been widely concerned. Photoelectrochemical (PEC) cell based on semiconductor materials is considered as an effective way in response to these issues. Many semiconductor materials, such as TiO2, BiVO4, and MoS2, etc. have been applied as promising electrodes. The semiconductors for PEC reactions should have proper band structures. Moreover, whether the material can be prepared into films to obtain high­quality photoanode/cathode is also a key to the performance of PEC cells.

In chapter 1, we review the background of PEC and highlight some applications addressing energy and environmental issues. Next, we introduce the configuration of a general PEC cell associated with the basic mechanism. Varieties of synthesis methods such as chemical vapor deposition (CVD), pulsed laser deposition (PLD), hydrothermal, spin­coating, and doctor­blading, etc., were invented for the working electrode of PEC cells. In view of this, we provide a comprehensive overview in the recent research of the anodes and cathodes.

In chapter 2, we report an iodine­doped graphitic carbon nitride (g-­CN) film with an enhanced photoelectrochemical performance by charge transfer doping through non-covalent interactions. Experimental results show that the iodine­doped g­-CN film presents an improved photocurrent density (38.9 µA cm−2) three times that of pristine CN film (13.0 µA cm−2) at 1.23 V versus reversible hydrogen electrode. By density functional theory (DFT) and time­dependent DFT verifications, the I anion noncovalently attached on g­-CN film can act as an excellent electron­donor to significantly decrease the energy gap of g-­CN film and promote the charge carrier spatial separation of the photo­induced hole and electron, respectively localized on I and g­-CN film. Our work combining experimental and computational efforts demonstrates that the non-covalent interaction between the thin film and certain dopants also plays a crucial role in facilitating the charge carrier separation as well as broadening visible light absorption range, which may provide a useful modification strategy for extensive photocatalysis materials.

In chapter 3, we provide a surface metallic bismuth oxide (Bi2-xO3) film applied to nitrogen fixation reaction. Doctor­-blading method was first introduced into the fabrication of Bi2-xO3 film. Under the irradiation of solar light, the photothermal effect of metallic bismuth nanoparticles on the film surface coordinates with the modification of the bandgap of bismuth oxide by oxygen vacancies, the reaction barrier of breaking N≡N covalent bonds can be crossed. We reveal the mechanism of the formation of metallic bismuth and oxygen vacancy during the vacuum thermal treatment and obtain the optimal film BiO­-500 at 500 ℃. The results show that BiO-­500 also has the highest yield of ammonium ions.

In Chapter 4, a brief conclusion of the thesis work is summarized. By tuning the internal electronic structures of the semiconductor films, the PEC properties of the corresponding electrodes were highly improved. In the end, we provide an outlook on the development of PEC devices for various applications

    Research areas

  • Photoelectrochemical cell, Semiconductor films, Graphitic carbon nitride, Bismuth oxide, Water splitting, Nitrogen fixation