An Experimental Study On The Electrocatalytic Conversion Of CO₂ And H₂O

The conversion of CO₂ and H₂ O to liquid fuels using renewable energies is a research hotspot in recent years, this kind of liquid fuel could be utilized in the concept of near-zero-carbon-emission power plant forming a closed cycle of “renewable energy?unstable energy supply? +CO₂ + H₂ O àliquid fuelsàelectricity?stable energy supply? +CO₂ + H₂O”, which can not only play an important role in reducing CO₂ emission, but also can realize the conversion and storage of unstable renewable energies. So far, there are three main routes for the conversion of CO₂ and H₂O: CO hydrogenation, CO₂ hydrogenation and the direct conversion of CO₂ and H₂ O, in which the CO and H₂ comes from the electrolysis of H₂ O, and electrocatalysis and photocatalysis are the two main methods of the direct conversion of CO₂ and H₂ O.To comparatively study feasibility of the three main routes and the performance of the whole near-zero-carbon-emission power plant, the commercial software package Aspen Plus was used to build models and carry out the thermodynamic analysis. The results showed that when CO₂ conversion is below 42%, the optimum route is the hydrogenation of CO₂ and CO, while when CO₂ conversion is above 42%, the best route is the electrocatalytic conversion of CO₂ and H₂ O. Models were built respectively for the near-zero-carbon-emission power plant that adopts hydrogenation route or electrocatalysis route. The results indicated that when CO₂ is totally converted into liquid fuel, the two near-zero-carbon-emission power plants have almost the same CO₂ emission rate, however the near-zero-carbon-emission power plant has a better thermal efficiency. Hence, in the long run the study on the electrocatalytic conversion of CO₂ and H₂ O to liquid fuels has a profound meaning.In this thesis we proposed to use the cold plasma of corona discharge to activate CO₂ and developed the electrocatalytic reactor that using both corona discharge and proton exchange membrane, which can allow CO₂ and H₂ O to react in room temperature. The results showed that the yield of products is directly proportional to the input voltage of the corona discharge, while the yield of products has inverse relationship with the discharge distance between cathode and membrane. The forming of CO is owing to the impact of the highly energetic electrons and the local extremely high static field to CO₂ molecules. The forming of CH4 comes from the reaction of CO with hydrogen radical, and the reaction of the deposit carbon with H₂ or hydrogen radical. The introduction of carbon paper loaded with nano-CuO catalyst could enhance the production of long chain hydrocarbons, but in the meanwhile it inhibits the forming of H₂, CO and CH4. If the alcoholic products are formed, they will be dehydrated due to the hydroxyl which can easily capture a hydrogen radical, and finally turns out to be hydrocarbons.