Controlled Synthesis Of Novel Highly Ordered Nano-arrays And Their Photoelectrochemical Properties

Oxide nano-ordered arrays have wildly broad applications in photocatalysis,photoelectrochemical water splitting, and solar cells in that it highly ordered nanostructures and excellent physical and chemical properties. However, as TiO2 nanotube arrays, it can only absorb ultraviolet light; Fe2O3 nanotube arrays, although having a high light absorption capacity, but its carriers are easy to complex, And these hinder its application. And the operability of the conventional modifying method is poor; modified oxide semiconductor ordered arrays have not better photoelectrochemical properties. Some kinds of novel modified ways need to explore to improve their photoelectrochemical properties.In this paper, modifiing in anodic oxidation(situ self-assemble) and hydrogenation were applyed to fabricate nano-ordered arrays, and their growth regularity was revealed. After that,their photoelectrochemical properties and photoelectric conversion mechanism were studied.In a certain electrolyte, anodic oxidation method was used to prepare nanotube arrays(NTAs),with a constant sheet metals or alloys(Ti, Ti-0.2Pd, Fe-0.5Ti) being the anode and graphite as the cathode. Different nanotube arrays were obtained with controlling series of parameters.After this step, hydrogen treatment was carried on TiO2 NTAs and Ti-Pd-O NTAs. The changes of shape and structure about samples were characteried by SEM, EDS, XRD and XPS, and the propreties of light absorption and photoelectrochemical were studied. And this reseach found that:(1) In an electrolyte consisting of 0.5wt% NH4 F and 0.1 M phosphoric acid electrolyte,TiO2 NTAs,with the diameter of 85 nm and long of 630 nm, were preduced at the voltage of20 V for 1h, and treated at 550℃. Anatase crystal contained few Rutil of TiO2 NTAs has best photoelectric properties with the highest photocurrent density of 0.53 mA / cm2 and the max light conversion efficiency of 0.38%. This sample as a precursur, anealed in H2 air at 450 ℃for 3h, with a concentration of 0.3atm, and exhibit an extreme value. Its highest photocurrent density is 1.4 mA / cm2, 2.64 times of without hydrogenated; and the max photoconversion efficiency is 1.16%, 3 times of unhydrogenated.(2) In an electrolyte consisting of 0.5wt% NH4 F and 0.1 mol/L phosphoric acid electrolyte, Ti-Pd-O NTAs,with the diameter of 90 nm, wall thickness of 14 nm and long of600 nm, were fabricated at the voltage of 20 V for 1h, and treated at 550 ℃. It has best photoelectric properties with the highest photocurrent density of 0.66mA/cm2 and the maxphotoconversion efficiency of 0.48%. Ti-Pd-O NTAs is anealed in H2 air at 400 ℃ for 3h,and exhibit a extreme value. Its highest photocurrent density is 0.92 mA / cm2, and the max photoconversion efficiency is 0.66%, 1.40 times of unhydrogenated Ti-Pd-O NTAs and 1.7times of unhydrogenated TiO2 NTAs.(3) In a glycol electrolyte containing 0.5wt% NH4 F and 3.0vol%H2O, Ti-Pd-O NTAs which were fabricated at the voltage of 30 Vfor 12h, and treated at 550 ℃. obtain better photoelectric properties with the highest photocurrent density of 0.62mA/cm2, and the max photoconversion efficiency of 0.46%, respectively. And then they were anealed in H2 air at500 ℃ for 3h, and exhibit a better photoelectric properties with the highest photocurrent density of 0.75 mA / cm2, and the max photoconversion efficiency of 0.66%, 1.4 times of the unhydrogenated Ti-Pd-O NTAs and 1.9 times of unhydrogenated TiO2 NTAs.(4) In a glycol electrolyte electrolyte containing 0.3wt% NH4 F and 3.0vol%H2O Fe-Ti-O NTAs, with inner diameter of 35 nm and length of 1.6μm was produced at the voltage of 50 V for 15 minutes, and was treated at 400℃. Fe2O3 NTAs which contained few Fe3O4, has better visible absorb and photoelectric properties with the photocurrent density of 0.03mA/cm2. Ti4+as a donor state and formed capture centers to promote their photoelectrochemical properties.Through the reseaches of situ self-assembled doping and surface hydrogenated, it is found that in certain temperature, surface hydrogenated can effectively improve the photoelectrochemical properties of semiconductor nano-ordered array. It mainly due to the formation of oxygen vacancies and disordered surface, and thereby the carrier density is increased and the transmission efficiency of the light-generated electrons and holes are promoted. In situ self-assembly doping, impurity levels formed and their performance is improved. And those two modification methods show some synergistic effect. In this thesis,Through two kinds of novel modified ways, self-assembly doped and surface hydrogenated,photoelectrochemical properties of semiconductor nano-ordered arrays is improved,promoting its applications in photovoltaic device.