| Under the background of "carbon peak and carbon neutralization",greenhouse gas emission reduction and reuse are of great importance.CO2 is one of the main greenhouse gases,and can also be regarded as an excellent carbon source with no toxicity,high chemical stability,low cost and easy availability.Based on molten salt electrolysis,it has been reported that CO2 can be captured and transformed into carbon materials.However,the single regulation measure of CO2 molten salt electrolysis,complex and disordered structure and low graphitization degree of carbon materials seriously restrict its application prospect as functional materials.In fact,CO2 in molten salt will inevitably generate carbon containing oxate intermediates.Therefore,considering its essential conversion characteristics,a more valuable route and method for electroconversion of CO2 into high value-added carbonaceous materials in molten salt can be developed.In addition,vanadium slag as vanadium extraction is an important raw material.Vanadium oxysalt(such as NaVO3)is an inevitable intermediate product in the vanadium extraction process.In the traditional vanadium extraction treatment of vanadium oxysalt,high emission links such as leaching,roasting and reduction calcination are used,which does not meet the development needs of green sustainable metallurgical industry.In recent years,the preparation of high-value materials by electrolysis technology has attracted extensive attention because of its advantages such as short process flow,green pollution-free emission and controllable product composition/structure.In particular,compared with aqueous solution medium,molten salt electrolysis technology has the advantages of wide electrochemical window,anhydrous solvation effect,less side reactions and high product controllability due to the absence of water.Metal oxide as raw material in the molten salt electrolysis is often used.However,oxides with relatively high purity still depends on the traditional thermal reduction method.The problems of long process,heavy pollution and high energy consumption are still prominent.Considering the electrochemical extraction of aluminum in molten salt,soluble raw are the key to continuous and efficient metallurgy.Then,based on the characteristics of soluble carbon and vanadium oxysalt are the key intermediates in the extraction process,whether it is possible to realize the one-step conversion of carbon and vanadium oxysalt to prepare high value-added carbon-vanadium materials.Due to excellent physical and chemical properties,carbon materials and vanadium-based materials can be widely used in catalysis,energy storage,national defense and aviation,alloy additives and other fields.This idea can prepare high value-added functional materials,shorten the process flow and avoid pollution emission,which is in line with the concept of green metallurgy.Therefore,a new idea of preparing high value-added carbon vanadium materials by molten salt electrolysis with CO2 and soluble NaVO3 extracted from vanadium slag as raw materials is proposed in this paper.The law of electroreduction of vanadate into carbon vanadium composites while CO2 capture is transformed into carbon is systematically studied;The electrochemical mechanism of molten salt in the process of converting carbon vanadium materials was clarified;The regulation mechanism of product was konwed;In addition,the feasibility of electrochemical in-situ catalytic conversion of CO2 to high graphitization carbon materials by vanadate(NaVO3)was explored,the behavior transformation and mechanism of NaVO3 in the process of electroconversion of molten salt from CO2 to high graphitization carbon were explored,and the basic system of high value-added carbon vanadium materials by CO electroconversion of CO2 vanadate(NaVO3)molten salt was constructed.In addition,based on COMSOL simulation,the structure of continuous CO2 conversion electrolytic cell is designed,and a conceptual system of CO2 molten salt capture and electrochemical carbon fixation is proposed,which provides an idea for continuous industrial large-scale molten salt conversion of carbon or carbon vanadium materials.At present,the main research results are as follows:(1)A vanadium-based powder material system with carbon composite by electroconversion of CO2 and NaVO3 was constructed.During the co-electrolysis of CO2 and NaVO3 in CaCl2 molten salt,CO32-and VO43-in molten salt as electroactive ions are confirmed,respectively.CO32-is first reduced to CO22-and then to carbon.VO43-is reduced to VO2-,which combines with Ca2+ in molten salt to form CaV2O4.Under deep regulation,a large number of VO2-ions were accumulated in the cathode,the competition reaction between Ca2+ and VO2-ions was reduced.VO2-preferentially self-combines to form V2O3.In addition,in CaCl2NaCl-CaO(1.0wt%)molten salt,under the conditions of 600℃ and cell voltage of 3.0V,when CO2 flow rate was reduced to 10mL min-1,high-purity VC ceramic materials were prepared.Among them,CO32-and VO3-as electroactive ions are electroreduced to carbon and vanadium carbide through transfer of 4 electrons and 5 electrons in 2 steps,respectively.After VO3-through transfer of 2 electrons are first reduced to VO2-ions,there are two possible paths to form vanadium carbide.One is that VO2-continues to obtain 3 electrons meanwhile reacts with electrodeposited carbon for electroreduction to vanadium carbide;The other is that VO2-ions are first electrically reduced to metal vanadium,and then react quickly with carbon to form vanadium carbide.In final,Carbon composite CaV2O4 and vanadium carbide powder materials are of broad application prospects in microwave absorption and energy storage.(2)The feasibility of NaVO3 electroreduction in-situ catalytic conversion of CO2 to high graphitized carbon was explored.And the method of NaVO3 in-situ catalytic electroreduction of CO2 to high graphitized carbon was developed.In CaCl2-NaCl-CaO(1.0wt%)molten salt,the catalytic graphitization of vanadium carbide by in-situ electroreduction of NaVO3 on CO2 electroconversion is not obvious.When NaVO3 is added into Na2CO3-K2CO3 molten salt,the pre-reaction occurs.Vanadium as electroactive ion V2O74-.CO32-exists in molten salt,which is easier to be electroreduced than V2O74-.CO32-and V2O74-undergo one-step 4 electron transfer and are reduced to C and V2O3 respectively.V2O3 can spontaneously react with Na2O and Na2CO3 in molten salt to convert into vanadate and accelerate the generation of carbon.V2O3 electroreduction and vanadate generation achieve a perfect cycle.At the same time,CO2 can be continuously and homogeneously converted into high graphitization carbon at the cathode.By increasing the concentration of NaVO3 in molten salt,cell pressure and electrolysis time,the graphitization degree of deposited carbon can be improved,and ID/IG value of regulated carbon can be reduced to 0.428.(3)The electrolyzer structure of continuous CO2 electroconversion is designed.And the conceptual system of CO2 capture and electrochemical carbon sequestration is conceived.The designed industrial continuous CO2 molten salt electroconversion cell structure is more reasonable than monomer cell with direct CO2 gas capture electrolytic mixing.That is,the electrode structure of double cathode(top)and anode(bottom)is arranged up and down,CO2 capture cell is separated from the electrolytic cell.The molten salt with saturated carbon concentration is directly introduced into the electrolytic cell for electroconversion.Based on the new cell structure,a continuous industrial electrolytic process of CO2 is proposed.Under this process,not only the continuous conversion of CO2 can be realized,but also the continuous co-electroconversion of high value-added carbonvanadium composites through adding soluble vanadate and CO2 can be expanded. |
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