Theoretical Research On Solar-driven Hydrocarbons Production Via CO₂/H₂O And Experimental Study On The Electrolysis System

With the greenhouse effect,energy shortage and other issues becoming increasingly serious,resource utilization of carbon dioxide is becoming more and more important.On the basis of STEP（Solar Thermal Electrochemical Production）theory,we successfully constructed the electrolysis system which will turn CO₂/H₂O into hydrocarbon.The electrochemical unit with high temperature uses molten mixed salt alkali carbonate as electrolyte and realizes the regeneration of carbonate-alkaline electrolyte using the intermediate product Li₂O,Na₂O,K₂O to absorb CO₂/H₂O,so as to build a complete cycle which will effectively turns CO₂/H₂O into hydrocarbon.In this experiment,the thermodynamic data of the reaction which will turns CO₂/H₂O into hydrocarbon are calculated when the temperature is between 298K and 1000K.?G°（hydrocarbon generating reaction from CO₂/H₂O electrolysis）>0,the reaction can not occur spontaneously;the theory decomposition potentials of CO₂ and H₂O decrease sharply with the increasing temperature.The value of E°（methane and ethylene generating reaction from CO₂/H₂O electrolysis）changes a little with the increasing temperature,the absolute value of E°（acetylene generating reaction from CO₂/H₂O electrolysis）decrease sharply with the increasing temperature.Theoretical analysis results show that heating or work on the system from other external force field could makes the reaction which will turn CO₂/H₂O into hydrocarbon happen possibly.We can use the solar photovoltaic and photothermal effect respectively to drive the reaction process.The electrochemical properties of the reaction system and the influence factors of product are investigated.The gas products are characterized by GC、FTIR、SEM and XPS.The results show that the type and the composition of the products changed significantly by the influence of electrolyte type,molar ratio of raw materials,current density and electrolytic temperature.Experimental results show that Li_0.896Na_0.625K_0.479CO₃-2KOH is the optimal electrolytic hydrocarbon generation system.When the electrolytic cell temperature is 500℃using Metal-1 as cathode（20 cm²）and Metal-4 as anode（20 cm²）under the proportion of n_C:n_H=1:2 with 1A constant current for 4h in electrolysis system,there is a large amount of hydrocarbon generation in the product.Methane volume content is 46.65%.At the same time,the formation of ethylene,propylene and other active components.This system successfully converted CO₂/H₂O into hydrocarbon,and realized the resource utilization of CO₂.