| Environmental conditions have become of primary importance at the present time for all people and for the next generation. The conditions become worse each day, and this entire situation occurs because of human activities. One of the main activities yielding a negative impact on the environment is the production of energy. Daily progress always needs energy, and the main sources of energy to date are provided via the combustion of fossil fuels, which can increase air pollution and the emission of greenhouse gasses. To overcome these problems, a new technology of pollution treatment and energy production must be developed.As a very important semiconductor material, TiO2 has been widely used as the photocatalyst for the elimination of environmental pollutants and as the electrocatalyst for energy production in fuel cells.However, when used as the photocatalyst for the elimination of environmental pollutants, TiO2 usuallly works under ultraviolet light due to their large energy band gap (e.g.～3.2 eV for anatase TiO2), which fairly limit their utilizations under solar light radiation to decompose organic pollutants. In addition, severe recombination of photo-generated electron-hole pairs in TiO2 restricts their large-scale applications as well. Extensive studies aiming at the production of efficient and visible-light responsive TiO2 using simple methods have been carried out to improve its photocatalytic activities. In this work, anatase TiO2 (A-TiO2), rutile TiO2 (R-TiO2), N and F-codoped anatase TiO2 (N-F-TiO2) and N-doped anatase TiO2 (N-TiO2) were prepared with a simple hydrolysis method at a low temperature, which were then characterized in detail by various techniques, such as X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), Brunauer-Emmett-Teller (BET), Diffuse Reflectance UV-vis Spectra (DRS), X-ray Photoelectron Spectroscopy (XPS) and Flourescent Emission Spectra (FES). The photocatlytic activities of N-F-TiO2, N-TiO2 and pure TiO2 (in anatase and rutile phases) were compared by degradation of methylene blue (MB) in aqueous solutions under UV light, visible light illumination and also with the synergy of electric field.Fuel cells have a tremendous attraction to researchers due to the clean, high efficiency, and dependable sources for energy. The cathode oxygen reduction reaction (ORR) is one of the key challenges in developing fuel cells. In particular, TiO2 has ever been proposed as an excellent candidate for the supporting material as electrocatalysts in fuel cell due to its synergistic effect to metal catalysts. In this work, we reported a facile route to prepare rGO supported TiO2 as non-metal catalysts for oxygen reduction. We also use TiO2/rGO composit as a carrier to load noble metal Pt, Pd and Pt-Pd alloy as the cathode electrocatalyst:Pt/TiO2/rGO, Pd/TiO2/rGO and Pt-Pd/TiO2/rGO. Structural and morphological properties were characterized by XRD, SEM, TEM, XPS and Raman spectra (RM). The electrochemical properties were evaluated using Cyclic Voltammetry (CV), Tafel test, Nyquist test and Current-time (i-t) test. The electrocatalyst kinetic was examined by Rotating Disk Electrode (RDE) and Rotating Ring Disk Electrode (RRDE).The results show that:(1) Nanosized TiO2 (anatase, rutile) and highly-efficient visible-light driven N-F-TiO2 and N-TiO2 photocatalysts were prepared by a simple hydrolysis method at a low temperature, with which the composition and structure of materials can be readily modified.(2) N-F-TiO2 and N-TiO2 had the characteristics of smaller crystalline size, broader light absorption spectrum and lower charge recombination than pure TiO2. Most importantly, more efficient photocatalytic activity under both ultra-violet and visible light was observed. The obtained N-F-TiO2 and N-TiO2 nanomaterials show considerable potential for water treatment under sunlight irradiation.(3) The photo-degradation performance of TiO2 degreed with the synergy of electric field, the reason may be part of the loss of photocarrier for photocarrier were neutralization with the positive and negative charge of the electric field before forming to overoxidation groups, it can be deduced that the electric field inhibitate the photocatalytic performance of TiO2 catalyst. It is also found that the degradation of Methylene blue in our study is satisfied with Langmuir-Chinshelwood function mode.(4) TiO2/rGO composits for oxygen reduction reaction were prepared by a simple hydrolysis method at a low temperature. The onset potential of oxygen reduction reaction (ORR) under the catalysis of TiO2/rGO is about-0.20 V (vs. Hg/Hg2Cl2) and the corresponding electron transfer number of ORR is 3.98, which means that the ORR are major happened through 4-electron style. TiO2/rGO catalyst has high catalytic for ORR and better stability than the commercial Pt(20%)/C catalyst in alkaline electrolyte.(5) The onset potential of oxygen reduction under the catalyst of Pt/TiO2/rG0, Pd/TiO2/rGO, Pt-Pd/TiO2/rGO were about -0.20V too, the exchange current density obtained by the Koutecky-Levich theory were all about 10-6-10-5 mA/cm2. The current still remained about 88% of their initial after chronoamperometric test for 16,000 s. Nevertheless, The commercial Pt(20%)/C catalyst only remained 74% of its initial current. TiO2/rGO and low noble loaded TiO2/rGO hybrid shows great promise as a high activity catalyst for ORR, which could be used as a promising material for practical fuel cell application. |
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