CN112760669A - Flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under large current condition - Google Patents
Flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under large current condition Download PDFInfo
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Abstract
A flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under a large current condition relates to an electrocatalytic carbon dioxide reduction method. The invention aims to solve the problem of the existing electrocatalysis of CO2The problems of low catalytic selectivity and poor system stability in the reduction technology. The preparation method comprises the following steps: firstly, preparing a gas diffusion electrode; secondly, assembling equipment; and thirdly, reduction. The invention is used for stably realizing high-efficiency electrocatalysis of CO under the condition of large current2Reduced flow electrolysis.
Description
Technical Field
The invention relates to a method for electrocatalytic carbon dioxide reduction.
Background
With the continuous development of society, the demand of human beings on energy is more and more, but traditional fossil energy such as coal, oil, natural gas belongs to primary energy, and its reserves are limited, and the energy crisis is inevitable. And the use of traditional fossil energy can make CO in the atmosphere2The concentration is continuously increased, so that the greenhouse effect is increasingly intensified, a series of environmental problems are brought, and the normal life of human beings is seriously influenced.
At present, CO2Resource recoveryThe technology mainly comprises electrochemical reduction, thermal reduction, photochemical reduction and the like. Due to CO2The bond energy of carbon-oxygen bond (C ═ O) in the molecule is up to 750kJ/mol, the thermodynamic property is stable, and CO is ensured2The reaction conditions required for the reduction are severe and performance limited. In the thermal catalysis of CO2In hydrogenation, the reaction temperature is often above 400 ℃, and CO is limited2The application environment of the reduction technology; and photocatalyzing CO2The reduction technology still has the defects of low energy conversion efficiency and CO2Poor adsorption effect and the like, and limits the industrial application of the adsorbent.
With the increasing maturity of hydroelectric power, wind power and solar power generation technologies, the proportion of new energy electric power in the current energy structure is gradually increased, and the power utilization cost is continuously reduced. However, due to the limitation of natural environment, the discontinuity of power generation of the new energy sources exists, and the storage of the residual energy becomes an important problem. This is electrocatalytic CO2Reduction provides a developmental opportunity for fuels or industrial feedstocks. Compared with the prior art, the electrocatalysis technology has the advantages of mild reaction conditions, simple experimental conditions and easy industrial industrialization, and provides an effective way for the sealing of the artificial carbon cycle.
Currently aimed at electrocatalytic CO2The reduction is mostly still in the laboratory stage, the reactors used are mostly conventional three-electrode H-cells, the reactant CO2The molecules need to dissolve in the electrolyte and then transfer mass to the electrode surface by diffusion to participate in the reaction. CO due to the relatively long diffusion mass transfer distance2Low solubility in aqueous electrolytes, severely limiting CO2The reduction efficiency and the reaction current are usually 10mA/cm2Compared with the industrial standard (200 mA/cm) obtained by technical economic analysis at present2) There is still a great gap, which is far from sufficient for industrialization. Although some research is currently conducted by taking fuel cell technology as a reference, the Gas Diffusion Electrode (GDE) is used to replace the traditional cathode reaction electrode, and the CO is reduced under a larger current2. But due to electrocatalysis of CO2The differences in the principles and technical details of reduction and fuel cell reactions have led to some fuel cell testing devices being applied to CO2Often occurs during reductionThe phenomena of leakage, gas leakage, or catalyst poisoning of the gas diffusion electrode often occur for several tens of minutes to several hours, and the system is deactivated, and thus, the system stability is poor, and it is difficult to maintain stable operation for a long time.
Disclosure of Invention
The invention aims to solve the problem of the existing electrocatalysis of CO2The problems of low catalytic selectivity and poor system stability in the reduction technology, and provides a flow electrolysis method which is applied to stably realize high-efficiency electrocatalytic carbon dioxide reduction under the condition of large current.
Firstly, preparing a gas diffusion electrode:
firstly, weighing: dissolving copper salt and iron salt in a solvent, adding a surfactant, and stirring and mixing for 10-120 min under the condition that the rotation speed is 500-1000 rpm to obtain a reaction solution;
the molar ratio of the copper salt to the iron salt is (1-999): 1; the volume ratio of the substance of the copper salt to the solvent in the first step is (0.5-2) mmol:100 mL; the volume ratio of the substance amount of the surfactant to the solvent in the first step is (0.5-2) mmol:100 mL;
secondly, reduction: introducing argon or nitrogen into the reaction solution for 10-60 min under the condition of ice-water bath, and then adding NaBH4Dissolving in solvent to obtain NaBH4The solution is prepared by adding NaBH in ice water bath at dropping speed of 0.1-1 mL/min and stirring speed of 1000-1300 rpm4Dripping the solution into the reaction solution, and reacting for 10-120 min to obtain a primary product solution;
the NaBH4NaBH in solution4The molar ratio of the copper salt to the copper salt in the first step is (10-100): 1;
thirdly, washing and separating: under the condition that the rotating speed is 7800 rpm-10000 rpm, separating the primary product solution for 5 min-10 min, then washing with absolute ethyl alcohol or normal hexane, and finally drying to obtain a primary product;
fourthly, removing the ligand: under the condition of argon or nitrogen atmosphere and the temperature of 473K-773K, treating the primary product for 1 h-4 h, and finally dispersing the primary product in n-hexane for later use to obtain a CuFe catalyst;
dispersing the CuFe catalyst in a solvent to obtain catalyst ink, spraying the catalyst ink on the gas diffusion layer by an air brush method, and finally drying to obtain a gas diffusion electrode;
the volume ratio of the mass of the CuFe catalyst to the solvent in the first step is (5-10) mg:1 mL;
secondly, equipment assembly:
using a graphite rod as an electrode, pretreating the electrolyte for 1-24 h under the condition of constant current of 0.1-1 mA to obtain the pretreated electrolyte, and utilizing a three-chamber flow electrolytic cell which is sequentially filled with CO2Gas flow cell, catholyte flow cell and anolyte flow cell, CO2A gas diffusion electrode is arranged between the gas flow chamber and the cathode liquid flow chamber, and CO is introduced by the gas diffusion electrode2The gas flow chamber is separated from the cathode flow chamber, an anion exchange membrane is arranged between the cathode flow chamber and the anode flow chamber, the cathode flow chamber and the anode flow chamber are separated by the anion exchange membrane and then sealed, an anode counter electrode is arranged in the anode flow chamber, a reference electrode is arranged in the cathode flow chamber, a cathode flow bottle is communicated with the cathode flow chamber through a guide pipe, an anode flow bottle is communicated with the anode flow chamber through a guide pipe, electrolyte subjected to pretreatment is poured into the cathode flow bottle and the anode flow bottle, CO is2The gas flow chamber is made of stainless steel, and finally the anode and the cathode of the power supply are respectively connected with the anode counter electrode and the CO2The outer surfaces of the gas flow chambers are connected;
thirdly, reduction:
injecting the pretreated electrolyte into the cathode flow chamber and the anode flow chamber respectively at a flow rate of 1 mL/min-100 mL/min, and controlling CO by using a gas flowmeter2Gas inflow of CO2The flow rate of the gas flow chamber is 1 mL/min-100 mL/min, a constant current mode or a constant voltage mode is used, and the current density is 50mA/cm2～1000mA/cm2Or electrocatalysis of CO under the condition that the voltage of the reversible hydrogen electrode is 0V-15V2Reducing, collecting the liquid flowing out of the cathode flow chamber and the liquid flowing out of the anode flow chamberAnd then separating and purifying a liquid phase product and electrolyte from the liquid flowing out of the cathode liquid flow chamber, separating and purifying a gas phase product and electrolyte from the liquid flowing out of the anode liquid flow chamber, circulating the separated electrolyte to the cathode liquid flow chamber and the anode liquid flow chamber at the flow speed of 1-100 mL/min, collecting a cathode gas product by a cathode gas storage tank, collecting an anode gas product by an anode gas storage tank, and collecting a liquid phase product by a cathode liquid storage tank, namely finishing the flow electrolysis method for stably realizing the high-efficiency electrocatalysis carbon dioxide reduction under the condition of large current.
The invention has the beneficial effects that:
1. the gas diffusion electrode is adopted to replace the traditional cathode electrode, and when the prepared CuFe catalyst is used, the Fe has stronger adsorption strength to the intermediate product CO, so that the CO is promoted2Initial activation rate of (A) and thus excellent electrocatalytic CO2Reducing power. Can realize the purpose of high current (more than 200 mA/cm) when using the alkaline electrolyte2) The selectivity to ethylene is over 50%.
2. The invention adopts the replacement of the ion exchange membrane and the gas diffusion layer and the change of the material of the reactor (the anode and the cathode of a power supply can be respectively connected with the anode counter electrode and the CO2The outer surfaces of the gas flow chambers are communicated), the catalyst loading mode is optimized, and the like, so that the problems of liquid leakage, gas leakage or catalyst poisoning easily occurring in the process of using the gas diffusion electrode are solved, the stability of the reaction system is improved, the reaction system can stably work for more than 10 hours, and the efficient and stable electrocatalytic reduction of CO is realized2。
The invention is used for a flow electrolysis method which is applied to stably realize efficient electrocatalysis carbon dioxide reduction under the condition of large current.
Drawings
FIG. 1 is a schematic diagram of a flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under a large current condition, wherein 1 is CO2A gas flow chamber, 2 is a cathode flow chamber, 3 is an anode flow chamber, 4 is a cathode flow bottle, 5 is an anode flow bottle, 6 is a cathode gas storage tank, 7 is a cathode liquid storage tank, 8 is an anode gas storage tank,9 is a gas diffusion electrode, 10 is an anion exchange membrane, and 11 is an anode counter electrode;
fig. 2 is a graph showing the surface morphology and the cross-sectional morphology of a catalytic layer prepared by different methods, wherein a is the surface morphology of the gas diffusion electrode prepared in the first example, b is the surface morphology of the gas diffusion electrode prepared in the first comparative experiment, c is the surface morphology of the gas diffusion electrode prepared in the second comparative experiment, d is the cross-sectional morphology of the gas diffusion electrode prepared in the first example, e is the cross-sectional morphology of the gas diffusion electrode prepared in the first comparative experiment, and f is the cross-sectional morphology of the gas diffusion electrode prepared in the second comparative experiment;
FIG. 3 shows the temperature at 200mA cm-2Gas diffusion electrode CO prepared by different CuFe catalyst loading modes under constant current2RR test results, 1 for example one electrocatalytic carbon dioxide reduction, 2 for comparative experiment one electrocatalytic carbon dioxide reduction, and 3 for comparative experiment two electrocatalytic carbon dioxide reduction;
FIG. 4 shows C under different electrolyte conditions2H4The selectivity changes along with the current density, wherein 1 is electrocatalytic carbon dioxide reduction of the first embodiment, and 2 is electrocatalytic carbon dioxide reduction of the second embodiment;
FIG. 5 shows the temperature at 200mA cm-2Electrocatalysis of CO when the second electrolyte of the example is KOH solution under constant current2The result of the stability test of (1) is a curve of the applied potential with time, and 2 is C2H4The selectivity of (a) over time.
Detailed Description
The first embodiment is as follows: specifically, referring to fig. 1, the flowing electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under a high current condition according to the present embodiment is completed according to the following steps:
firstly, preparing a gas diffusion electrode:
firstly, weighing: dissolving copper salt and iron salt in a solvent, adding a surfactant, and stirring and mixing for 10-120 min under the condition that the rotation speed is 500-1000 rpm to obtain a reaction solution;
the molar ratio of the copper salt to the iron salt is (1-999): 1; the volume ratio of the substance of the copper salt to the solvent in the first step is (0.5-2) mmol:100 mL; the volume ratio of the substance amount of the surfactant to the solvent in the first step is (0.5-2) mmol:100 mL;
secondly, reduction: introducing argon or nitrogen into the reaction solution for 10-60 min under the condition of ice-water bath, and then adding NaBH4Dissolving in solvent to obtain NaBH4The solution is prepared by adding NaBH in ice water bath at dropping speed of 0.1-1 mL/min and stirring speed of 1000-1300 rpm4Dripping the solution into the reaction solution, and reacting for 10-120 min to obtain a primary product solution;
the NaBH4NaBH in solution4The molar ratio of the copper salt to the copper salt in the first step is (10-100): 1;
thirdly, washing and separating: under the condition that the rotating speed is 7800 rpm-10000 rpm, separating the primary product solution for 5 min-10 min, then washing with absolute ethyl alcohol or normal hexane, and finally drying to obtain a primary product;
fourthly, removing the ligand: under the condition of argon or nitrogen atmosphere and the temperature of 473K-773K, treating the primary product for 1 h-4 h, and finally dispersing the primary product in n-hexane for later use to obtain a CuFe catalyst;
dispersing the CuFe catalyst in a solvent to obtain catalyst ink, spraying the catalyst ink on the gas diffusion layer by an air brush method, and finally drying to obtain a gas diffusion electrode;
the volume ratio of the mass of the CuFe catalyst to the solvent in the first step is (5-10) mg:1 mL;
secondly, equipment assembly:
using a graphite rod as an electrode, pretreating the electrolyte for 1-24 h under the condition of constant current of 0.1-1 mA to obtain the pretreated electrolyte, and utilizing a three-chamber flow electrolytic cell which is sequentially filled with CO2Gas flow cell, catholyte flow cell and anolyte flow cell, CO2A gas diffusion electrode is arranged between the gas flow chamber and the cathode liquid flow chamber, and CO is introduced by the gas diffusion electrode2The gas flow chamber is separated from the cathode flow chamber and between the cathode flow chamber and the anode flow chamberSetting anion exchange membrane, separating cathode flow chamber from anode flow chamber by anion exchange membrane, sealing, setting anode counter electrode in anode flow chamber, setting reference electrode in cathode flow chamber, communicating cathode flow bottle with cathode flow chamber via duct, communicating anode flow bottle with anode flow chamber via duct, pouring pretreated electrolyte into cathode flow bottle and anode flow bottle, CO2The gas flow chamber is made of stainless steel, and finally the anode and the cathode of the power supply are respectively connected with the anode counter electrode and the CO2The outer surfaces of the gas flow chambers are connected;
thirdly, reduction:
injecting the pretreated electrolyte into the cathode flow chamber and the anode flow chamber respectively at a flow rate of 1 mL/min-100 mL/min, and controlling CO by using a gas flowmeter2Gas inflow of CO2The flow rate of the gas flow chamber is 1 mL/min-100 mL/min, a constant current mode or a constant voltage mode is used, and the current density is 50mA/cm2～1000mA/cm2Or electrocatalysis of CO under the condition that the voltage of the reversible hydrogen electrode is 0V-15V2And (2) reducing, namely collecting liquid flowing out of the cathode liquid flow chamber and liquid flowing out of the anode liquid flow chamber, then separating and purifying liquid-phase products and electrolyte from the liquid flowing out of the cathode liquid flow chamber, separating and purifying gas-phase products and electrolyte from the liquid flowing out of the anode liquid flow chamber, circulating the separated electrolyte to the cathode liquid flow chamber and the anode liquid flow chamber at the flow speed of 1-100 mL/min, collecting cathode gas products by a cathode gas storage tank, collecting anode gas products by an anode gas storage tank, and collecting liquid-phase products by a cathode liquid storage tank, namely finishing the flow electrolysis method for stably realizing high-efficiency electrocatalysis carbon dioxide reduction under the condition of large current.
In the first step of the present embodiment, Ar or N is introduced into the solution under the condition of ice-water bath2Gas to remove dissolved oxygen.
In the first embodiment, the surfactant is removed.
The anion exchange membrane is used in the embodiment, so that the phenomenon that the anode counter electrode is dissolved under the action of an electric field, migrates to the cathode through the cation exchange membrane and deposits on the cathode catalyst and is poisoned by the catalyst is avoided.
The electrolyte pretreated by the embodiment removes trace heavy metal impurities in the electrolyte.
The beneficial effects of the embodiment are as follows:
1. the gas diffusion electrode is adopted to replace the traditional cathode electrode, and when the prepared CuFe catalyst is used, the Fe has stronger adsorption strength to the intermediate product CO, so that the CO is promoted2Initial activation rate of (A) and thus excellent electrocatalytic CO2Reducing power. Can realize the purpose of high current (more than 200 mA/cm) when using the alkaline electrolyte2) The selectivity to ethylene is over 50%.
2. The embodiment adopts the replacement of the ion exchange membrane and the gas diffusion layer and the change of the material of the reactor (the anode and the cathode of the power supply can be respectively connected with the anode counter electrode and the CO2The outer surfaces of the gas flow chambers are communicated), the catalyst loading mode is optimized, and the like, so that the problems of liquid leakage, gas leakage or catalyst poisoning easily occurring in the process of using the gas diffusion electrode are solved, the stability of the reaction system is improved, the reaction system can stably work for more than 10 hours, and the efficient and stable electrocatalytic reduction of CO is realized2。
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the solvent in the first step and the second step is organic solvent containing alcohol or water; the alcohol-containing organic solvent is triethylene glycol, glycol or glycerol; the solvent in the first step is mixed solution of isopropanol and Nafion or ethanol; the volume ratio of the isopropanol to the Nafion in the mixed solution of the isopropanol and the Nafion is (10-100): 1. The rest is the same as the first embodiment.
The third concrete implementation mode: this embodiment is different from the first or second embodiment in that: the copper salt in the first step is cupric nitrate, cupric acetate, copper acetylacetonate, cupric chloride, cupric sulfate or cuprous acetate. The other is the same as in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: the ferric salt in the first step is ferric triacetylacetonate, ferric chloride, ferric nitrate, ferric sulfate or ferrous sulfate. The others are the same as the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: the surfactant in the first step is polyvinylpyrrolidone, N-methylpyrrolidone, octadecylamine hydrochloride or secondary alkyl sodium sulfonate. The rest is the same as the first to fourth embodiments.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: the gas diffusion layer in the first step is carbon paper or a polytetrafluoroethylene film. The rest is the same as the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: when the gas diffusion layer is carbon paper, spraying catalyst ink on the gas diffusion layer by an air brush method under the condition that the temperature of the gas diffusion layer is 20-100 ℃ in the first step, and finally drying to obtain the gas diffusion electrode, wherein the loading amount of CuFe catalyst in the catalyst ink is 0.5mg/cm2～3mg/cm2(ii) a When the gas diffusion layer is a polytetrafluoroethylene film, in the first step, under the condition that the temperature of the gas diffusion layer is room temperature, the catalyst ink, the carbon black and the graphite are sequentially sprayed on the gas diffusion layer by an air brush method, and finally, the gas diffusion electrode is obtained by drying, wherein the loading amounts of the CuFe catalyst, the carbon black and the graphite in the catalyst ink are all 0.5mg/cm2～3mg/cm2. The others are the same as the first to sixth embodiments.
The polytetrafluoroethylene of the embodiment has stable chemical property and hydrophobicity, and can improve the stability of the reactor. Carbon black and graphite are coated to enhance the electrical conductivity of the gas diffusion electrode.
The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: the concentration of the electrolyte in the second step is 0.01-10 mol/L; the electrolyte in the second step is LiOH solution, NaOH solution, KOH solution, RbOH solution, CsOH solution or LiHCO solution3Solutions of、NaHCO3Solution, KHCO3Solution, RbHCO3Solution and CsHCO3And (3) solution. The rest is the same as the first to seventh embodiments.
The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: when the electrolyte is neutral electrolyte, the reference electrode is an Ag/AgCl electrode or a saturated calomel electrode; when the electrolyte is an alkaline electrolyte, the reference electrode is an Hg/HgO electrode. The other points are the same as those in the first to eighth embodiments.
The detailed implementation mode is ten: the present embodiment differs from one of the first to ninth embodiments in that: the anode counter electrode In the second step is a Pt sheet, a Pt net, a Ni net, foam Ni or In2O3. The other points are the same as those in the first to ninth embodiments.
The following examples were used to demonstrate the beneficial effects of the present invention:
the first embodiment is as follows:
a flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the condition of large current is completed according to the following steps:
firstly, preparing a gas diffusion electrode:
firstly, weighing: dissolving copper salt and iron salt in a solvent, adding a surfactant, and stirring and mixing for 3min under the condition that the rotation speed is 1000rpm to obtain a reaction solution;
the molar ratio of the copper salt to the iron salt is 99: 1; the volume ratio of the substance of the copper salt to the solvent in the first step is 1mmol:100 mL; the volume ratio of the substance amount of the surfactant to the solvent in the first step (i) is 1mmol:100 mL;
secondly, reduction: introducing argon into the reaction solution for 30min under the condition of ice-water bath, and then introducing NaBH4Dissolving in solvent to obtain NaBH4The solution is prepared by adding NaBH in ice water bath at dropping speed of 0.1mL/min and stirring speed of 1300rpm4Dripping the solution into the reaction solution, and reacting for 30min to obtain a primary product solution;
the NaBH4NaBH in solution4The molar ratio of the copper salt to the copper salt in the first step is 20: 1;
thirdly, washing and separating: separating the primary product solution for 5min under the condition that the rotation speed is 10000rpm, then washing the primary product solution for five times by using absolute ethyl alcohol, and finally drying the primary product solution to obtain a primary product;
fourthly, removing the ligand: under the condition of argon atmosphere and temperature of 673K, treating the primary product for 3h, and finally dispersing the primary product in n-hexane for later use to obtain a CuFe catalyst;
dispersing CuFe catalyst in solvent to obtain catalyst ink, spraying the catalyst ink on the gas diffusion layer by an air brush method under the condition that the temperature of the gas diffusion layer is 80 ℃, and finally drying to obtain a gas diffusion electrode;
the volume ratio of the mass of the CuFe catalyst to the solvent in the first step is 8mg:1 mL; the loading amount of the CuFe catalyst in the catalyst ink is 1mg/cm2；
Secondly, equipment assembly:
using a graphite rod as an electrode, pretreating the electrolyte for 24 hours under the condition of constant current of 1mA to obtain a pretreated electrolyte, and utilizing a three-chamber flow electrolytic cell which is sequentially provided with CO2Gas flow cell, catholyte flow cell and anolyte flow cell, CO2A gas diffusion electrode is arranged between the gas flow chamber and the cathode liquid flow chamber, and CO is introduced by the gas diffusion electrode2The gas flow chamber is separated from the cathode flow chamber, an anion exchange membrane is arranged between the cathode flow chamber and the anode flow chamber, the cathode flow chamber and the anode flow chamber are separated by the anion exchange membrane and then sealed, an anode counter electrode is arranged in the anode flow chamber, a reference electrode is arranged in the cathode flow chamber, a cathode flow bottle is communicated with the cathode flow chamber through a guide pipe, an anode flow bottle is communicated with the anode flow chamber through a guide pipe, electrolyte subjected to pretreatment is poured into the cathode flow bottle and the anode flow bottle, CO is2The gas flow chamber is made of stainless steel, and finally the anode and the cathode of the power supply are respectively connected with the anode counter electrode and the CO2The outer surfaces of the gas flow chambers are connected;
thirdly, reduction:
injecting the pretreated electrolyte into the cathode flow chamber and the anode flow chamber at a flow rate of 5mL/min, respectively, and controlling CO with a gas flow meter2Gas inflow of CO2The flow rate of the gas flow cell was 30mL/min, a constant current mode was used, and the current density was 50mA/cm2～250mA/cm2Under the conditions of (1), electrocatalysis of CO2Reducing, namely collecting liquid flowing out of a cathode liquid flow chamber and liquid flowing out of an anode liquid flow chamber, then separating and purifying liquid-phase products and electrolyte from the liquid flowing out of the cathode liquid flow chamber, separating and purifying gas-phase products and the electrolyte from the liquid flowing out of the anode liquid flow chamber, circulating the separated electrolyte to the cathode liquid flow chamber and the anode liquid flow chamber at the flow rate of 5mL/min, collecting cathode gas products by a cathode gas storage tank, collecting anode gas products by an anode gas storage tank, and collecting the liquid-phase products by the cathode liquid storage tank, namely finishing the flow electrolysis method for stably realizing the high-efficiency electrocatalysis carbon dioxide reduction under the condition of large current;
the solvents in the first step and the second step are all ethylene glycol; the solvent in the first step is mixed solution of isopropanol and Nafion; the volume ratio of the isopropanol to the Nafion in the mixed solution of the isopropanol and the Nafion is 30: 1.
The copper salt in the first step is copper nitrate.
The ferric salt in the first step is ferric nitrate.
The surfactant in the first step is polyvinylpyrrolidone.
The gas diffusion layer in the first-fifth step is carbon paper.
The concentration of the electrolyte in the second step is 0.5mol/L or 1 mol/L; the electrolyte in the second step is KHCO3And (3) solution.
The electrolyte is alkaline electrolyte, and the reference electrode is an Hg/HgO electrode.
And the anode pair electrode in the second step is a Ni net.
And in the first step, performing air brush spraying by using a Master Airbrush VC16-B22 spray gun system.
Example two: the difference between the present embodiment and the first embodiment is: and the electrolyte in the second step is NaOH solution. The rest is the same as the first embodiment.
Example three: the difference between the present embodiment and the first embodiment is: when the gas diffusion layer is the polytetrafluoroethylene film in the first step, spraying catalyst ink, carbon black and graphite on the gas diffusion layer in sequence by an air brush method in the first step and the fifth step under the condition that the temperature of the gas diffusion layer is room temperature, and finally drying to obtain the gas diffusion electrode, wherein the loading amounts of CuFe catalyst, carbon black and graphite in the catalyst ink are all 1mg/cm2. The rest is the same as the first embodiment.
Comparison experiment one: the comparative experiment differs from the first example in that: in the first step, the loading amount is 1mg/cm2Coating the catalyst ink on the gas diffusion layer by a blade coating method, specifically comprising the following steps: the catalyst ink is uniformly coated on the surface of the carbon paper by using an KTQ-II adjustable coating device to move at a constant speed under the action of a certain pressure. The rest is the same as the first embodiment.
Comparative experiment two: the comparative experiment differs from the first example in that: in the first step, the loading amount is 1mg/cm2Coating catalyst ink on a gas diffusion layer by a drop casting method, specifically, the method comprises the following steps: and uniformly dripping the catalyst ink on the surface of the carbon paper by using a dropper or a pipette. The rest is the same as the first embodiment.
Fig. 2 is a graph showing the surface morphology and the cross-sectional morphology of a catalytic layer prepared by different methods, wherein a is the surface morphology of the gas diffusion electrode prepared in the first example, b is the surface morphology of the gas diffusion electrode prepared in the first comparative experiment, c is the surface morphology of the gas diffusion electrode prepared in the second comparative experiment, d is the cross-sectional morphology of the gas diffusion electrode prepared in the first example, e is the cross-sectional morphology of the gas diffusion electrode prepared in the first comparative experiment, and f is the cross-sectional morphology of the gas diffusion electrode prepared in the second comparative experiment; as can be seen from the graphs a to c, CuFe nanoparticles are obviously agglomerated in different catalyst loading modes, and the surface uniformity of the catalyst layer loaded by the air brush method is relatively high. As can be seen from the d-f graphs, the catalyst loading amounts are all 1mg/cm2In the case of (2), the catalytic layer of the sample was prepared by the air brush methodThe thickness is maximum and can reach 25.1 mu m, which means that the internal porosity of the catalyst layer is higher, and the catalyst layer is beneficial to gas-phase and liquid-phase mass transfer; the thickness of the catalytic layer of the gas diffusion electrode loaded by the drop casting method is the minimum, and is only 7.68 mu m, and the internal porosity of the catalytic layer is low.
KHCO of 0.5mol/L for gas diffusion electrodes obtained by different loading methods3Electrocatalytic test under medium constant current condition at 200mA/cm2Electrocatalysis of CO on gas diffusion electrode prepared by contrast experiment one-blade coating method and gas diffusion electrode prepared by contrast experiment two-drop casting method under constant current2All of which exhibit blow-by, some of the gas phase products and CO2The gas flows out along with the catholyte after being desorbed on the surface of the gas diffusion electrode in the form of bubbles, so that the applied potential of the cathode obviously fluctuates. However, the gas diffusion electrode prepared by the gas brush method in the embodiment still has no overflow phenomenon after 1h stability test, and the cathode potential is relatively stable.
The resulting gas phase product was analyzed by gas chromatography, and FIG. 3 shows that the concentration was 200mA cm-2Gas diffusion electrode CO prepared by different CuFe catalyst loading modes under constant current2RR test results, 1 for example one electrocatalytic carbon dioxide reduction, 2 for comparative experiment one electrocatalytic carbon dioxide reduction, and 3 for comparative experiment two electrocatalytic carbon dioxide reduction. Wherein the gas diffusion electrode pair H is prepared by a blade coating method and a drop casting method2The selectivity of CO and the electrolyte is obviously higher than that of a gas brush method sample, and the main reason is that the electrolyte fills the pores in the gas diffusion layer and blocks CO2The catalyst layer is partially submerged, a three-phase reaction interface is damaged, and the further reduction of the adsorbed CO intermediate product is prevented while HER side reactions are promoted. Gas diffusion electrode pair C prepared by gas brush method2H4The selectivity is the highest and reaches 23.24 percent. While the gas diffusion electrode prepared in the first example was carried out at 100mA/cm2Lower pair C2H4The selectivity of (2) was tested and found to be 44%, with only a very small amount of CH present4And (3) obtaining the product. It was thus demonstrated that a stable three-phase reaction interface favours further reduction of the adsorbed CO intermediate.
ExamplesTwo pairs of CuFe nano-particle catalyst loaded gas diffusion electrodes are used for making CO under the condition of constant current in KOH of 1mol/L2RR test, and KHCO at 1mol/L as in example one3Comparing the test results in the electrolyte, and measuring the obtained C2H4The selectivity as a function of current density is shown in fig. 4. FIG. 4 shows C under different electrolyte conditions2H4The selectivity changes along with the current density, wherein 1 is electrocatalytic carbon dioxide reduction of the first embodiment, and 2 is electrocatalytic carbon dioxide reduction of the second embodiment; as can be seen, the reaction temperature is higher than that of KOH and KHCO3In the electrolyte C2H4The selectivity has similar trend along with the change of current density, and is all at 100mA/cm2The current density reaches a maximum value, wherein C in KOH2H4The selectivity reaches 60.16 percent and is obviously higher than KHCO344.93% of (1). C at different current densities when KOH is used as the electrolyte2H4The selectivity of (A) is generally higher than that of (B) in KHCO3The test result in (1) proves that the alkaline electrolyte selectively reduces CO for the CuFe catalyst2Is C2H4The promotion of (1).
200mA/cm gas diffusion electrode loaded with CuFe nano-particle catalyst2The stability test was carried out at a constant current, and the results are shown in FIG. 5, where FIG. 5 shows the stability test at 200mA · cm-2Electrocatalysis of CO when the second electrolyte of the example is KOH solution under constant current2The result of the stability test of (1) is a curve of the applied potential with time, and 2 is C2H4The selectivity of (a) over time. C2H4The selectivity of (A) is increased with time and is increased first, and the maximum value of 61.97 percent is reached at 1 h; subsequent decrease in hydrophobicity of the carbon paper results in C2H4The selectivity of (a) gradually decreases, and decreases to 46.16% at 5h, and the catalyst gradually deactivates. At the same time H2The selectivity is increased and the cathode reduction potential is gradually increased. But can maintain more than 50% of C as a whole2H4The selective reaction of (2) is more than 4h, and has obvious advantages compared with most experiments at present.
Example three gas diffusion layers were polytetrafluoroethylene membranes,the polytetrafluoroethylene has stable chemical properties and stronger hydrophobicity, and can keep long-acting hydrophobicity in electrocatalysis reaction when used as a gas diffusion layer so as to stably maintain a three-phase reaction interface and avoid the phenomena of liquid leakage and gas leakage. Gas diffusion electrode made of Teflon film at 200mA/cm2A constant current stability test was performed, C2H4The selectivity of (A) is kept at about 50 percent and can last for more than 10 hours.
Claims (10)
1. A flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the condition of large current is characterized by comprising the following steps:
firstly, preparing a gas diffusion electrode:
firstly, weighing: dissolving copper salt and iron salt in a solvent, adding a surfactant, and stirring and mixing for 10-120 min under the condition that the rotation speed is 500-1000 rpm to obtain a reaction solution;
the molar ratio of the copper salt to the iron salt is (1-999): 1; the volume ratio of the substance of the copper salt to the solvent in the first step is (0.5-2) mmol:100 mL; the volume ratio of the substance amount of the surfactant to the solvent in the first step is (0.5-2) mmol:100 mL;
secondly, reduction: introducing argon or nitrogen into the reaction solution for 10-60 min under the condition of ice-water bath, and then adding NaBH4Dissolving in solvent to obtain NaBH4The solution is prepared by adding NaBH in ice water bath at dropping speed of 0.1-1 mL/min and stirring speed of 1000-1300 rpm4Dripping the solution into the reaction solution, and reacting for 10-120 min to obtain a primary product solution;
the NaBH4NaBH in solution4The molar ratio of the copper salt to the copper salt in the first step is (10-100): 1;
thirdly, washing and separating: under the condition that the rotating speed is 7800 rpm-10000 rpm, separating the primary product solution for 5 min-10 min, then washing with absolute ethyl alcohol or normal hexane, and finally drying to obtain a primary product;
fourthly, removing the ligand: under the condition of argon or nitrogen atmosphere and the temperature of 473K-773K, treating the primary product for 1 h-4 h, and finally dispersing the primary product in n-hexane for later use to obtain a CuFe catalyst;
dispersing the CuFe catalyst in a solvent to obtain catalyst ink, spraying the catalyst ink on the gas diffusion layer by an air brush method, and finally drying to obtain a gas diffusion electrode;
the volume ratio of the mass of the CuFe catalyst to the solvent in the first step is (5-10) mg:1 mL;
secondly, equipment assembly:
using a graphite rod as an electrode, pretreating the electrolyte for 1-24 h under the condition of constant current of 0.1-1 mA to obtain the pretreated electrolyte, and utilizing a three-chamber flow electrolytic cell which is sequentially filled with CO2Gas flow cell, catholyte flow cell and anolyte flow cell, CO2A gas diffusion electrode is arranged between the gas flow chamber and the cathode liquid flow chamber, and CO is introduced by the gas diffusion electrode2The gas flow chamber is separated from the cathode flow chamber, an anion exchange membrane is arranged between the cathode flow chamber and the anode flow chamber, the cathode flow chamber and the anode flow chamber are separated by the anion exchange membrane and then sealed, an anode counter electrode is arranged in the anode flow chamber, a reference electrode is arranged in the cathode flow chamber, a cathode flow bottle is communicated with the cathode flow chamber through a guide pipe, an anode flow bottle is communicated with the anode flow chamber through a guide pipe, electrolyte subjected to pretreatment is poured into the cathode flow bottle and the anode flow bottle, CO is2The gas flow chamber is made of stainless steel, and finally the anode and the cathode of the power supply are respectively connected with the anode counter electrode and the CO2The outer surfaces of the gas flow chambers are connected;
thirdly, reduction:
injecting the pretreated electrolyte into the cathode flow chamber and the anode flow chamber respectively at a flow rate of 1 mL/min-100 mL/min, and controlling CO by using a gas flowmeter2Gas inflow of CO2The flow rate of the gas flow chamber is 1 mL/min-100 mL/min, a constant current mode or a constant voltage mode is used, and the current density is 50mA/cm2～1000mA/cm2Or a condition of 0V to 15V with respect to the reversible hydrogen electrode voltageBy electrocatalysis of CO2And (2) reducing, namely collecting liquid flowing out of the cathode liquid flow chamber and liquid flowing out of the anode liquid flow chamber, then separating and purifying liquid-phase products and electrolyte from the liquid flowing out of the cathode liquid flow chamber, separating and purifying gas-phase products and electrolyte from the liquid flowing out of the anode liquid flow chamber, circulating the separated electrolyte to the cathode liquid flow chamber and the anode liquid flow chamber at the flow speed of 1-100 mL/min, collecting cathode gas products by a cathode gas storage tank, collecting anode gas products by an anode gas storage tank, and collecting liquid-phase products by a cathode liquid storage tank, namely finishing the flow electrolysis method for stably realizing high-efficiency electrocatalysis carbon dioxide reduction under the condition of large current.
2. The flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the condition of large current according to claim 1, wherein the solvents in the first step I and the first step II are both alcohol-containing organic solvents or water; the alcohol-containing organic solvent is triethylene glycol, glycol or glycerol; the solvent in the first step is mixed solution of isopropanol and Nafion or ethanol; the volume ratio of the isopropanol to the Nafion in the mixed solution of the isopropanol and the Nafion is (10-100): 1.
3. The flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the large-current condition as claimed in claim 1, wherein the copper salt in the first step is cupric nitrate, cupric acetate, cupric acetylacetonate, cupric chloride, cupric sulfate or cuprous acetate.
4. The flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the large-current condition according to claim 1, wherein the ferric salt in the first step is ferric triacetylacetone, ferric chloride, ferric nitrate, ferric sulfate or ferrous sulfate.
5. The flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the large-current condition according to claim 1, wherein the surfactant in the first step is polyvinylpyrrolidone, N-methylpyrrolidone, octadecylamine hydrochloride or sodium secondary alkylsulfonate.
6. The flow electrolysis method for stably realizing high-efficiency electrocatalytic carbon dioxide reduction under high-current conditions according to claim 1, wherein the gas diffusion layer in the first step (c) is carbon paper or a polytetrafluoroethylene membrane.
7. The flow electrolysis method for stably realizing high-efficiency electrocatalytic carbon dioxide reduction under high-current conditions according to claim 6, wherein when the gas diffusion layer is carbon paper, in the first step, the catalyst ink is sprayed on the gas diffusion layer by an air brush method under the condition that the temperature of the gas diffusion layer is 20-100 ℃, and finally, the gas diffusion electrode is obtained by drying, wherein the loading amount of the CuFe catalyst in the catalyst ink is 0.5mg/cm2～3mg/cm2(ii) a When the gas diffusion layer is a polytetrafluoroethylene film, in the first step, under the condition that the temperature of the gas diffusion layer is room temperature, the catalyst ink, the carbon black and the graphite are sequentially sprayed on the gas diffusion layer by an air brush method, and finally, the gas diffusion electrode is obtained by drying, wherein the loading amounts of the CuFe catalyst, the carbon black and the graphite in the catalyst ink are all 0.5mg/cm2～3mg/cm2。
8. The flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the large current condition according to claim 1, wherein the concentration of the electrolyte in the second step is 0.01-10 mol/L; the electrolyte in the second step is LiOH solution, NaOH solution, KOH solution, RbOH solution, CsOH solution or LiHCO solution3Solution, NaHCO3Solution, KHCO3Solution, RbHCO3Solution and CsHCO3And (3) solution.
9. The flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under the large-current condition according to claim 8, wherein when the electrolyte is a neutral electrolyte, the reference electrode is an Ag/AgCl electrode or a saturated calomel electrode; when the electrolyte is an alkaline electrolyte, the reference electrode is an Hg/HgO electrode.
10. The flow electrolysis method for stably realizing efficient electrocatalytic carbon dioxide reduction under high current condition according to claim 1, wherein the anode counter electrode In the second step is Pt sheet, Pt net, Ni net, foam Ni or In2O3。
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