Study On The Generation Of Hydrocarbon-rich Fuel Gas Via CO₂/H₂O Co-electrolysis In Molten Salts

The climate change caused by over-dependence on fossil energy and large amount emission of carbon dioxide seriously damages the human living environment.Developing green,efficient and environmentally friendly CO₂ capture and transformation methods is an important way to alleviate greenhouse effect and realize resource recycling.Molten salt electrolyte has wide operating temperature window and high ion migration rate.It is an excellent electrochemical reaction medium which has been widely used in the research of CO₂capture and conversion.Electrochemical reaction can be chemically reacted rapidly in the electrolyte of molten salts.In this paper,molten carbonates and hydroxides are innovatively selected as electrolytes to controllably product hydrocarbon-rich fuel gas via CO₂ and H₂O co-electrolysis with high efficiency.The liquid eutectic molten salt electrolyte has excellent heat and mass transfer performance.Oxygen is the only oxidation produt that was generated on the surface of anode.CO₂ and H₂O are rapidly absorbed by the metallic oxide transformed from carbonates and hydroxides.Thereby,the eutectic molten salts can be regenerated and recycled to product hydrocarbon-rich fuel gas.CO₂ and H₂O are absorbed and transformed in molten salts and formed a chemical recycle process.The main study contents of this paper are as follows.(1)Electrochemical reaction pattern of CO₂ and H₂O in molten salts is proposed and set up,and the possible electrochemical reactions on the electrode surface are deeply studied.Based on the above research,the Gibbs free energy and theoretical electrolytic potential are calculated to analyze the difficulty of reaction.The carbon deposition reaction occurrs preferentially in Li₂CO₃,indicating that Li₂CO₃ is the essential components of electrolyte.LiOH is preferred to reduc into H₂ rather than metal Li,which is beneficial to increase current efficiency.Methane is the main product of hydrocarbon,and other alkanes are less.(2)The eutectic salt of carbonates and hydroxides is selected as electrolyte to transform CO₂ and H₂O to hydrocarbon-rich fuel gas at high temperature by adjusting electrolysis parameters of electrolyte composition,temperature,current,voltage,gas atmosphere and electrode materials.At applied potential of 2.0 V in Li_0.85Na_0.61K_0.54CO₃+0.2LiOH,operating temperature of 575°C,20 cm² Ni and Fe as anode and cathode respectively,the synthesized fuel gaseous product contains of 48.41%CH₄,and efficiency is 90.32%.(3)Combined the theoretical study of nickel oxidation reaction and result of electrochemical testing curve,the corrosion process of Ni anode is studied.Modified nickel anode with Ni-Ni O coating is produced by in-situ oxidation and heating oxidation.The working life of modified nickel anode is investigated in molten salts,and the solubility of Ni O is also studied.With the increase of temperature,the solubility of Ni O in molten salts declines.When Ca O content is 1.5 mol%,the solubility of Ni O decreases from 0.145 wt%to0.107 wt%.When Ba O content is 3 mol%,the solubility of Ni O decreases to 0.118 wt%.(4)The regeneration ability of molten salt is investigated by adding different content of Li₂O to simulate the conversion process of carbonate and hydroxide to metal oxide.The small-scale experiment of CO₂/H₂O to methane is carried out to investigate the key control factor in this process.At applied potential of 2.0 V in 300g Li_0.85Na_0.61K_0.54CO₃+0.2LiOH+0.05Ca O,operating temperature of 575°C,50 cm² Ni and Fe as anode and cathode respectively,CO₂ flow rate of 180mL/h,Ar flow rate of 600mL/h,H₂O flow rate is 0.15 g/h,the producing rate of CH₄ is 48.78mL/h,while H₂ is 45.36mL/h,and current efficiency is84.53%.In this paper,CO₂ and H₂O are highly efficient and controllable electrochemical reduced to hydrocarbon-rich fuel gas in molten salt system by using green and renewable electric energy.It not only develops a new-type clean fuel gas,but also realizes harmless and high value-added utilization of CO₂,providing a new idea and direction for CO₂ emission reduction and sustainable development.