Photoelectrochemical Water Oxidation Of LaTaON₂ Under Visible Light Irradiation

With rapid population growth and economic development, oil, natural gas, coal and other fossil fuels have become increasingly depleted. Meanwhile, the extensive use of fossil fuels has caused a serious threat to the ecological environment. Obviously, looking for clean reusable energy has become an urgent task for the future development of mankind. Solar energy is green, abundant and clean renewable energy, which is one of the main sources of energy consumption in the future. The photoelectrochemical (PEC) cell is an effective way of utilizing solar energy which can be converted solar energy to hydrogen energy. For photoelectrochemical cells, the core component is the photoanode film which has to stable, high efficiency and low cost. In this study, we have focused on an n-type LaTaON2 film with a suitable band structure, excellent visible light absorption and non-toxic, etc., which is rising up as a promising material for photoelectrochemical cells.Lanthanum tantalum oxynitride (LaTaON2) powders were prepared by one-step flux method (flux), the polymerized complex method (PC) and the solid state reaction (SSR), respectively. LaTaON2 photoanodes, which are fabricated by using LaTaON2 powders, are found to exhibit photoelectrochemical activity for overall water splitting, the research content mainly includes five parts:(1) The photocurrent for LaTaON2 photoelectrodes which was prepared by one-step flux method was ca0120 μA/cm2 at 1.5 VRHE in 1 M NaOH aqueous solutions (pH=13.6) under AM 1.5 G simulated sunlight irradiation (100 mW/cm2).(2) LaTaON2 is demonstrated to evolve H2 and O2 from water containing hole scavengers (methanol) and electron scavengers (Ag*), respectively, in reasonable agreement with the estimated band gap position by Mott-Schottky method and Tauc plot.(3) When added H2O2 into the NaOH electrolyte, the photocurrent was 3.6 times at 0.9 VRHE than that without the addition of H2O2, indicating that surface recombination processes existed. The photocurrent of LaTaON2 photoelectrode from back-side illumination is much larger than that from front-side illumination, suggesting that the photoelectrochemical property is mainly limited by poor continuous electron transport in the bulk.(4) In order to overcome the structure defects of LaTaON2-flux, the solid state method and the polymerized complex method were attempted to prepare the LaTaON2 particles as well. However, the poor charge transport is still the main limiting factor for high photoelectrochemical performance.(5) In addition, the possibility of defect-mediated bulk recombination could not be ruled out. We attempt to charge the ratio of La/Ta in order to figure out the ion defects. However, the photocurrent is lower than the beginning indicating the complex defects problem. We will further optimize the ratio of La/Ta for the purpose to improve the photoelectrochemical property of LaTaON2..