Preparation And Application Of Semiconductor Photoelectrodes For The Photoelectrocatalytic Reduction Of CO₂

In recent years,the energy crisis and environmental problems caused by the consuming of fossil fuels have aroused people's great concerns.Photoelectrocatalytic reduction of CO₂ to produce fuels and chemicals is of great significance to solve the energy crisis,and at the same time reduce the greenhouse effect.In this work,firstly,a new type of photoelectrocatalytic reactor was designed and fabricated.Then,the preparation and application of photoanodes for the photoelectrocatalytic reduction of CO₂ was investigated.Particularly,the ionic liquids were applied as electrolytes to perform the photoelectrocatalytic reduction of CO₂,due to their unique effect for absorption and transformation of CO₂.The main contents of each chapter are as follows:?1?The progress on the current utilization of CO₂ and the photoelectrocatalytic reduction of CO₂ are reviewed.Then,the research significance and research contents of this thesis are briefly described.?2?Firstly,black TiO₂ nanotube arrays were synthesized through an anodization method followed by high temperature hydrogenation.Subsequently,the morphology,crystal structure,optical absorption poperty and incident photon-to-current poperty of the as-obtained TiO₂-NTAs were probed and analysed using SEM,XRD,UV-vis and LSV,respectively.Specially the research are emphasised on the effects of anodic voltage,electrolyte composition and different post-treatment methods on the structure and morphology of the prepared TiO₂-NTAs,and the influence of high temperature hydrogenation on the photon-to-current property of the black TiO₂-NTAs.Finally,the photoelectrocatalytic reduction of CO₂ was studied by using the prepared black TiO₂-NTAs and the [C2MIm][BF4] aqueous solution as photoanode and the cathodic solution,respectively.The characterization results showed the TiO₂-NTAs with a regular arrangement,smooth tube walls and clean ends were successfully fabricated,under the condition of synthesized using glycerol electrolyte solution?containing 0.2M NH4 F and 0.15 M?NH4?2SO₄,5 vol% H2 O and 20 vol% ethylene glycol?,applied voltage of 45 V for 4 h and sonication in ethanol for 45 mins;black TiO₂-NTAs exhibited excellent photon-to-current property after high temperature hydrogenation at500 ? for 2 h.The results of photoelectrocatalytic reduction of CO₂ showed that themain product of CO₂ reduction is CO,and the efficiency of Faraday is 67.3% at the applied voltage of 2.1 V.?3?Firstly,the WO₃/BiVO₄ composite photoanode were prepared.Then the surface morphology,the cross-section structure and the photon-to-current property of the prepared WO₃/Bi VO₄ composite films were characterized by SEM and linear voltammetry technology,respectively.In current section,the effects of polyethylene glycol content in the precursor solution of WO₃,the thickness of WO₃ and Bi VO₄ on the photon-to-current property of WO₃/BiVO₄ composite films were mainly investigated.Finally,the photoelectrocatalytic reduction of CO₂ was carried out by using WO₃/Bi VO₄ composite film and the [NH2C3MIm]Br aqueous solution as photoanode and the cathodic solution,respectively.The characterization results showed that the WO₃/Bi VO₄ composite films with excellent photon-to-current property can be formed under the preparation conditions,in which 1 ml of polyethylene glycol was added,4 circles of spraying of precursor solution for WO₃ and2 circles for BiVO₄ were repeated.The results of photoelectrocatalytic reduction of CO₂ showed that the main product of CO₂ reduction is HCOOH,and the efficiency of Faraday can surprisingly reach as high as 94.1% when the applied voltage is 1.7 V.Additionally an impressive photon-to-chemical efficiency value of 0.11% was also observed at the applied voltage as low as 1.1 V.?4?The main research results of this thesis are briefly summarized,and the future works are proposed.