Using abundant water resources on the earth as raw materials and free solar energy as energy sources, photocatalytic decomposition of aquatic hydrogen is a promising hydrogen production technology. One research focus of photocatalytic hydrogen production is to find a suitable catalyst that can effectively absorb sunlight and produce enough support to participate in the electrochemical REDOX reaction of water decomposition. Titanium dioxide is a typical N-type semiconductor, which has the advantages of non-toxicity, good weather resistance and low cost, and has the potential to become a photoelectric cathode material. However, due to the wide band gap of titanium dioxide, short-wavelength light such as ultraviolet light is needed to excite electrons in the titanium dioxide gap band to the guide band, and charge-hole separation is difficult. This shortcoming limits the application of titanium dioxide in the field of photocatalysis, so the electrode material needs to be modified. Among the many modification methods of titanium dioxide, the method of introducing Magneli phase containing oxygen vacancy into the pure phase of titanium dioxide effectively improves the conductivity and photoelectric conversion efficiency of the material, and is regarded as one of the innovative strategies to improve the photocatalytic performance of titanium dioxide. In this paper, the author prepared a titanium oxide with a gradient oriented pore structure by using the freezing pouring method and carbothermal reduction method. The introduction of the oriented porous structure maintained the mechanical strength of the material and increased the specific surface area. The introduction of Magneli phase improved the charge-hole separation efficiency to a certain extent, and the photocurrent density and photocurrent conversion efficiency of titanium oxide were improved. Compared with titanium dioxide, the increase is significant. In this paper, the conductivity of titanium dioxide, partially reduced titanium oxide and fully reduced titanium oxide, as well as the photocurrent density and photoconversion efficiency of the three materials used as oriented porous photocathode materials are compared, and the reasons for the strong catalytic ability of gradient oriented porous titanium oxide are explained. It is precisely because of the introduction of an appropriate amount of Magneli phase that not only improves the conductivity of the material, but also avoids the formation of too many electron-hole composite centers, thus improving the photocurrent density and photoelectric conversion efficiency. In addition, compared with dense materials, porous materials increase the specific surface area of the material, the light receiving area of the material and the active site generating the photocurrent increase, and the photocurrent density and photoelectric conversion efficiency of graded oriented porous titanium oxide increase with the increase of porosity, which provides a new idea for the preparation of photoelectrode materials.
In this paper, the method of oxygen vacancy self-doping was used to modify oriented porous titanium dioxide to improve the difficulty of electron-hole separation of titanium dioxide. Among them, the gradient oriented porous reducing titanium dioxide photoelectrode with a porosity of 30 vol% achieves a photocurrent density of up to 9.14 mA/cm2 and a photoelectric conversion efficiency of 40.52%. Specific innovations are as follows: (1) The introduction of an appropriate amount of Magneli phase is helpful for electron-hole separation of titanium dioxide as a widely studied photocatalyst, whose photoelectric conversion efficiency needs to be improved. In this paper, the electrical and photoelectrical properties of three kinds of oriented porous photocathode materials, titanium dioxide, partially reduced titanium oxide and completely reduced titanium oxide, are compared with that of titanium dioxide, and it is found that the conductivity of partially reduced titanium oxide is significantly improved due to the existence of oxygen vacancy. Compared with the completely reduced titanium oxide, there is no large number of electron-hole recombination “trap” in its interior, maintaining a high electron-hole separation rate and a low electron-hole recombination rate, which is the main reason for the increase in the photocurrent density of partially reduced titanium oxide.
(2) Oriented porous structure improves photocurrent density and photoelectric conversion efficiency Materials with orientated porous structure have higher mechanical strength, and the specific surface area also increases with the increase of porosity, and due to the good connectivity between the pores, the material can better receive light. In this paper, a photocathode material with the highest photocurrent density and photoelectric conversion efficiency was determined by comparing the oriented porous titanium oxide photoelectrodes at different porosity levels.
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