| Since the industrial revolution in the middle of18th century, especially the recent10decades, the constant progress of science and improvement of technology meet people’s growing material and life needs. But on the other hand, it carries a heavy living environmental burden. The greenhouse effect mainly caused by CO2may leads to the melting glaciers, rising sea level, meteorological disasters such as typhoons and floods and also may cause the change of global climate layout of different regions. The scientists research on the fixation, transformation and utilization of CO2in order to ease the greenhouse effect. It is promising and meaningful to apply electrochemical techniques to reduce CO2.Methanol, ethanol and acetone are significant organic chemical raw materials, which can be respectively used in the basic chemicals production such as formaldehyde, formaldehyde, acetic acid, dimethyl sulfate, aldehyde, ether, epoxy resin, polycarbonate and so on. All of them are good solvents. Methanol is widely used as the solvent of paint, dye and varnish adhesives. Ethanol is good solvent for varnish, cosmetics, printing ink and paint remover while acetone can be applied as coating and adhesives solvents. All in all, methanol, ethanol and acetone as fuels and chemical analytical reagents are widely applied in the production of medicine, cosmetics and pesticide.The electrochemical reduction of CO2can not only reduce the atmospheric CO2concentration but also turns the waste into the wealth through the way into methanol, ethanol and acetone which are chemical raw materials. The current efficiency and selectivity of the production of CO2electrochemical reduction are still low. So it is necessary to find proper materials and modify or dope them to obtain materials with better catalytic properties for CO2electroreduction. This thesis focuses on the synthesis of organics especially acetone and methanol with carbon in low valence from CO2. The research contents are as follows: (1)The preparation and characterization of RuO2/Ti electrodes in three different methodsThe RuO2/Ti electrodes were prepared respectively by electrodeposition, electrodeposition followed by annealing or thermal decomposition on Ti substrate. The properties and morphologies of the electrodes were investigated by XRD and SEM. It is proved that RuO2can be achieved in catalytic layer and the morphologies were compared. The result of potentiostatic electrolysis indicates that the RuO2/Ti electrode prepared by thermal decomposition presents better catalytic activity.(2)The research of RuO2/Ti electrode with electrochemical techniquesThe RuO2/Ti electrode was researched and its stability was tested by CV, EIS and potentiostatic electrolysis. The conclusion is as follows:A method of CV positive sweep measurement after a potential hold for5min was applied while the direct CV measurement result is not obvious. Along with the negatively shifting of the holding potential, the anodic current increases, which may be a result of the increase of reduction products from CO2. The electrochemical system parameters was obtained by EIS equivalent circuit and the preliminary steps of CO2reduction mechanism were researched. The adsorption and reaction of active substances can be influenced by the change of potential. The tests and characterizations of RuO2/Ti electrode before and after several electrolysis indicate the electrode can be employed repeatedly for its good mechanical stability and electrochemical stability.(3)Test and electrolysis apply of Ti-doping RuO2-TiO2/Ti electrodes prepared by thermal decompositionOn the basis of RuO2/Ti electrode, the Ti was doped to prepare RuO2-TiO2/Ti electrodes with Ru:Ti ratios of4:1,3:2,2:3and1:4by thermal decomposition. The XRD patterns indicate Ti can be well doped into the catalytic layer to form RuO2-TiO2composite oxides electrodes. The Ti peak intensity increases with the Ti percent. SEM result indicates that particles from all the ratios of RuO2-TiO2/Ti electrodes in the catalytic layer are below100nm. When the Ru:Ti ratio is1:4, the dimension of particles is smallest between10nm to25nm. The RuO2-TiO2/Ti electrode with Ru:Ti ratio of2:3was researched by CV and EIS. The results of potentiostatic and galvanostatic electrolysis demonstrate that Ru:Ti ratio, potential and current density have important influence on the electroreduction products and current efficiencies. Acetone is the main product and also a small amount of methanol and ethanol are detected. When the electrolytic potential was set as-0.5V, current efficiency of acetone reached33.6%on RuO2-TiO2/Ti(3:2) electrode. When the current density was0.333mA/cm2, current efficiency of acetone reached36.3%on RuO2-TiO2/Ti(2:3) electrode.(4)The influence on CO2electrochemical reduction of electrolyzer A plate-and-frame structure electrolyzer was manufactured and the assembly of working and counter electrodes was designed. The larger RuO2-TiO2/Ti(2:3) electrode was chosen as the working electrode. A series of conditions and parameters were investigated by galvanostatic electrolysis such as the system is closed or not, the gas low rate, current, electric charge quantity and the types of supporting electrolyte. The result indicates that the system closed or not and the gas flow rate scarcely influence the products. When the current was1.875mA/cm2, current efficiency of acetone was7.13%which was relatively highest, while the current efficiency of ethanol was0.42%. The current efficiency of methanol was0.44%relatively highest when the current was1.563mA/cm2. When the charge was80C, methanol had a current efficiency of0.54%. When the charge was110C, ethanol had a current efficiency of0.44%. The current efficiency of acetone reached7.71%after120C charge passed the electrolyzer. The types of supporting electrolyte research show different supporting electrolytes have significant influence on the electrolysis results. |
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