CN113564629B - Bismuth-based material and preparation method and application thereof - Google Patents
Bismuth-based material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a bismuth-based material and a preparation method and application thereof. The preparation method of the bismuth-based material comprises the following steps: preparing the bismuth phosphate into the nano bismuth-based material by an electrochemical reduction method. The bismuth-based material prepared by the preparation method has higher oxygen atom embedding amount and can be used for reducing CO in electrocatalysis 2 The process of (2) can ensure the Faraday efficiency of formic acid, and has high energy utilization rate and good catalytic stability.
Description
Technical Field
The invention relates to a bismuth-based material and a preparation method and application thereof.
Background
With the progress of times and the development of science and technology, the demand of human beings on energy sources is more and more increased. The continuous combustion of fossil fuels in human life and industrial production leads to CO in the air 2 The content of the compound is greatly increased, and the global warming is accelerated, so that a series of environmental problems such as acid rain, sea level rise and the like are caused. How to remove CO in the atmosphere 2 Recovery and conversion to various organic chemical fuels is one of the great challenges facing sustainable development. Electrocatalytic reduction of CO 2 The reaction is well recognized to convert CO 2 Conversion into high added valueAn effective way of producing the product.
In electrocatalytic reduction of CO 2 In the reaction, liquid-phase formic acid is used for electrochemically reducing CO 2 The liquid phase formic acid is more convenient to store and transport than the gaseous product; but also has high hydrogen storage capacity, and is widely applied to a plurality of industrial processes as an important chemical intermediate.
Metals such as bismuth, tin, lead, mercury, indium and cobalt have been shown to convert CO in aqueous electrolytes 2 An efficient catalyst for reduction to formic acid. Among them, bismuth has become CO due to its low toxicity and environmental friendliness, and its excellent activity and selectivity 2 A baseline catalyst for the reduction of formic acid. Bismuth as catalyst is derived from a variety of precatalysts, e.g. BiOX (Cl, Br, I), Bi 2 O 2 CO 3 And bismuth-based metal organic frameworks, and the like. The existing document "Ultrathin biosheets from in situ copolymerization transformation for selective electrolytic CO 2 reduction to format; na Han, Yu wang.et.al, nat. commun, 2018(9)1320 "discloses a bismuth-based nanosheet made by reduction of a bisi nanosheet; the bismuth-based nanosheet is treated with 0.5M NaHCO 3 The faradaic efficiency of formic acid in the electrolyte of (2) is almost 100%, but it is required to be only 22mA cm at-1.41V (relative to a reversible hydrogen electrode) -2 (according to FIG. 3b at-1.65V SCE (i.e., -1.41V) RHE ) The Faraday efficiency was the highest, about 100%, corresponding to a current density of about 22mA cm in FIG. 3c -2 ) The energy utilization rate is low, and is only 54.5%.
Chinese patent document CN111604046A discloses a bismuth-based material, wherein nano-rod-shaped bismuth sulfide is used as a raw material for preparation, the content of subsurface solvent oxygen on the surface of the prepared bismuth-based nano-material is only 10% -15%, the faraday efficiency of formic acid is about 80%, and the energy utilization rate is only 51.7%.
Therefore, a bismuth-based nano material is urgently needed, which not only can ensure the faraday efficiency of formic acid, but also can improve the energy utilization rate, thereby further improving the electro-catalytic reduction of CO by the bismuth-based nano material 2 The efficiency of (c).
Disclosure of Invention
The invention aims to overcome the defect that the bismuth-based material in the prior art reduces CO in an electrocatalysis way 2 The middle cathode energy utilization efficiency needs to be further improved, and provides a bismuth-based material and a preparation method and application thereof. The bismuth-based material has higher oxygen atom insertion amount and can be used for reducing CO in electrocatalysis 2 Meanwhile, the method has better formic acid Faraday efficiency, excellent energy utilization rate and better catalytic stability.
Although those skilled in the art know that bismuth-based materials are used in electrocatalytic reduction of CO 2 The application finds that the bismuth-based material prepared by the bismuth phosphate through the electrochemical reduction method not only has better Faraday efficiency of formic acid, but also has higher energy utilization rate, thereby further improving the electrocatalytic reduction of CO 2 The efficiency of (c). The invention solves the technical problems by the following scheme:
the invention provides a preparation method of a bismuth-based material, which comprises the following steps: preparing the bismuth phosphate into the nano bismuth-based material by an electrochemical reduction method.
In the present invention, the bismuth phosphate may be various forms of bismuth phosphate prepared by a conventional method or commercially available bismuth phosphate. Preferably, the bismuth phosphate is columnar particles, and the length of the bismuth phosphate is in the range of 200nm to 2 μm, and the diameter of the bismuth phosphate is in the range of 100nm to 1 μm. Preferably, the crystal structure of the bismuth phosphate is a monoclinic crystal structure.
In the present invention, the bismuth phosphate can be prepared according to a conventional method in the art, and is preferably prepared by a hydrothermal method. The hydrothermal method is to perform hydrothermal reaction on a bismuth source precursor and a phosphorus source precursor in a hydrothermal solution. The hydrothermal solution (including bismuth source precursor, phosphorus source precursor and solvent), hydrothermal temperature, hydrothermal time and other operating conditions used in the hydrothermal method can be conventional in the art.
Wherein the hydrothermal solution contains the bismuth source precursor, the phosphorus source precursor and a solvent.
The bismuth source precursor may be selected from one or more of ethylenediaminetetraacetic acid bismuth, bismuth nitrate and bismuth chloride, preferably bismuth nitrate and/or bismuth chloride, more preferably bismuth nitrate, such as bismuth nitrate pentahydrate. The phosphorus source precursor may be sodium phosphate dodecahydrate. The molar ratio of the bismuth source precursor to the phosphorus source precursor is preferably 1: 1 to 1: 5; more preferably 1: 1 to 1: 4, e.g. 1: 2.
the solvent may be ethylene glycol and/or water.
The hydrothermal solution can be prepared by mixing the solution of the bismuth source precursor and the solution of the phosphorus source precursor, or by mixing the solution of the bismuth source precursor and the phosphorus source precursor, preferably by dropwise adding the solution of the phosphorus source precursor into the solution of the bismuth source precursor.
The concentration of the bismuth source precursor solution is preferably 0.5 to 1mol/L, for example, 0.67 mol/L. The concentration of the solution of the phosphorus source precursor is preferably 0.02-0.12 mol/L, more preferably 0.02-0.05 mol/L, such as 0.022mol/L or 0.044 mol/L.
The mixing is preferably carried out at room temperature (e.g., 25 ℃ C.) with stirring. The stirring time may be from 5 minutes to 2 hours, such as 30 minutes, 1 hour, or 2 hours.
Wherein the hydrothermal temperature is preferably in the range of 120 to 180 ℃, e.g. 140 ℃ or 160 ℃. The hydrothermal time is preferably in the range of 4 to 24 hours, for example 8 hours or 12 hours.
In a preferred embodiment, the hydrothermal temperature is 160 ℃ and the hydrothermal time is 4 hours.
In a preferred embodiment, the hydrothermal temperature is 140 ℃ and the hydrothermal time is 8 hours.
In a preferred embodiment, the hydrothermal temperature is 180 ℃ and the hydrothermal time is 12-24 hours.
In a preferred embodiment, the hydrothermal temperature is 120 ℃ and the hydrothermal time is 24 hours.
In a preferred embodiment of the present invention, the hydrothermal method is performed as follows: mixing the bismuth source precursor solution and the phosphorus source precursor solution, and carrying out hydrothermal reaction at 160 ℃ for 4 hours; wherein the molar ratio of the bismuth source precursor to the phosphorus source precursor is 1: 1.
in the present invention, the electrochemical reduction method is to electrochemically reduce bismuth phosphate to bismuth or bismuth oxide. The steps and conditions of the electrochemical reduction method can be carried out according to the conventional operation mode in the field, and specifically, the bismuth phosphate is prepared into a working electrode, and the reference electrode and a counter electrode are utilized to carry out in-situ electrochemical reduction.
The way of making the working electrode from the bismuth phosphate can be conventional in the art, and can be, for example: dispersing bismuth phosphate and perfluorinated sulfonic acid-polytetrafluoroethylene copolymer solution in ethanol, and performing ultrasonic treatment to prepare the working electrode. The mass concentration of the perfluorosulfonic acid-polytetrafluoroethylene copolymer solution is preferably 5 wt%. The perfluorosulfonic acid-polytetrafluoroethylene copolymer solution is also called Nafion solution and is generally commercially available.
The mass-volume ratio of the bismuth phosphate to the perfluorinated sulfonic acid-polytetrafluoroethylene copolymer solution can be 0.1-2 mg/mu L; preferably 0.25 mg/. mu.L.
The mass-to-volume ratio of the bismuth phosphate to the ethanol may be 1 to 50mg/mL, for example, 1 to 40mg/L, preferably 10 mg/mL.
The ultrasonic frequency of the ultrasonic wave can be 10-50 KHz. The ultrasonic time of the ultrasonic treatment can be 20-60 minutes. Preferably, the ultrasonic frequency is 40KHz, and the ultrasonic time is 30 minutes.
After the sonication, the resulting dispersion may be applied by drop coating uniformly onto a hydrophobic carbon paper, e.g., 1X 1cm 2 Thus, the working electrode can be manufactured.
Wherein the reference electrode can be an Ag/AgCl reference electrode. Preferably, the solution in the Ag/AgCl reference electrode is a 3M KCl solution. Wherein the counter electrode may be a platinum electrode.
Wherein the reduction potential of the electrochemical reduction may be conventional in the art, e.g. may be-0.6 to-1.2V relative to the reversible hydrogen electrode, further e.g. -0.7 to-1.1V relative to the reversible hydrogen electrode, preferably-0.9V relative to the reversible hydrogen electrode.
The time of the electrochemical reduction may be conventional in the art, and may be, for example, 20 to 60 minutes, preferably 30 minutes.
In a preferred embodiment: dispersing the bismuth phosphate and perfluorinated sulfonic acid-polytetrafluoroethylene copolymer solution in ethanol, performing ultrasonic treatment to prepare a working electrode, and performing in-situ electrochemical reduction by using Ag/AgCl as a reference electrode and a platinum electrode as a counter electrode.
The invention also provides the bismuth-based material prepared by the preparation method.
In the invention, the bismuth-based material is generally nano-sheet or nano-particle in shape.
Wherein, when the morphology of the bismuth-based material is a nano-sheet, the length and width of the nano-sheet are preferably 1-10 μm, and the thickness is preferably 5-15 nm.
Wherein, when the morphology of the bismuth-based material is nanoparticles, the particle size of the nanoparticles is preferably 50-150 nm.
The oxygen atom insertion amount on the surface of the bismuth-based material is preferably 35% to 60%, for example, 57.1%, 42.4%, and 38.6%, and more preferably 50% to 60%.
The invention also provides the application of the bismuth-based material in the electrocatalytic reduction of CO 2 As a catalyst.
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The reagents and starting materials used in the present invention are commercially available.
The invention has the beneficial effects that:
(1) the bismuth-based material of the invention is used for electrocatalytic reduction of CO 2 In the process, the Faraday efficiency of formic acid can be ensured, and meanwhile, the energy utilization rate is higher; in a preferred embodiment of the invention, up to 200mA cm in current density -2 In the process, the Faraday efficiency of the formic acid can reach more than 90 percent, and the energy utilization efficiency can reach 73 percent;
(2) the bismuth-based material has higher oxygen atom embedding amount which can reach 35 to 60 percent;
(3) the bismuth substrate of the present inventionElectrocatalytic reduction of CO from feedstock 2 Has good catalytic stability.
Drawings
FIG. 1 is Bi 4f and SEM images of PD-Bi1, PD-Bi2, and PD-Bi3 electrocatalyst XPS.
Figure 2 is an XRD and SEM, TEM, HRTEM image of PD-Bi1 electrocatalyst.
FIG. 3 is an electrochemical performance test of PD-Bi1, PD-Bi2, and PD-Bi3 electrocatalysts.
FIG. 4 is an electrocatalytic reduction of CO by PD-Bi1 electrocatalyst in H-type cells and flow cells 2 And (4) performance.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the invention thereto. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.
Example 1
Step (1): dropwise adding a precursor solution containing 1mmol of sodium phosphate dodecahydrate into a precursor solution containing 1mmol of bismuth nitrate pentahydrate, wherein the volumes of the two solutions are 45mL and 15mL respectively (namely the concentrations of the two precursors are 0.022mol/L and 0.067mol/L respectively), and stirring at room temperature for 30 minutes to obtain a mixed solution required by hydrothermal treatment.
Step (2): heating the mixed solution at 160 ℃ for 4 hours, washing and drying to obtain bismuth phosphate (marked as BiPO) 4 -1);
And (3): prepared BiPO 4 -1 powder 10mg and 40. mu.L Nafion solution (5 wt%) dispersed in 1mL ethanol, sonicated for 30 minutes, and uniformly drop-coated on a hydrophobic carbon paper as a working electrode (drop-coated area 1X 1 cm) 2 ). And (3) carrying out electrolytic reduction for 30 minutes under the reduction potential of-0.9V (relative to a reversible hydrogen electrode) by taking the electrode as a working electrode, Ag/AgCl (3M KCl) as a reference electrode and a platinum mesh electrode as a counter electrode to obtain the nano flaky bismuth-based material (recorded as PD-Bi 1).
The prepared bismuth-based nano material is in a nano sheet shape, the length and the width of the bismuth-based nano material are 1-10 mu m, and the thickness of the bismuth-based nano material is 5-15 nm.
Example 2
Step (1): dropwise adding a precursor solution containing 2mmol of sodium phosphate dodecahydrate into a precursor solution containing 1mmol of bismuth chloride, wherein the volumes of the two solutions are 45mL and 15mL respectively (namely the concentrations of the two precursors are 0.044mol/L and 0.067mol/L respectively), and stirring at room temperature for 1 hour to obtain a mixed solution required by hydrothermal treatment.
Step (2): the mixed solution is hydrothermally treated for 8 hours at the temperature of 140 ℃, washed and dried to obtain bismuth phosphate (marked as BiPO) 4 -1a);
And (3): prepared BiPO 4 -1a powder 10mg and 100. mu.L Nafion solution (5 wt%) were dispersed in 10mL of ethanol, sonicated for 20 minutes, and uniformly drop-coated on hydrophobic carbon paper as a working electrode (drop-coated area 1X 1 cm) 2 ). And (3) carrying out electrolytic reduction for 30 minutes under the reduction potential of-0.7V (relative to a reversible hydrogen electrode) by taking the electrode as a working electrode, Ag/AgCl (3M KCl) as a reference electrode and a platinum mesh electrode as a counter electrode to obtain the nano flaky bismuth-based material.
Example 3
Step (1): dropwise adding a precursor solution containing 4mmol of sodium phosphate dodecahydrate into a precursor solution containing 1mmol of bismuth nitrate pentahydrate, wherein the volumes of the two solutions are 45mL and 15mL respectively (namely the concentrations of the two precursors are 0.089mol/L and 0.067mol/L respectively), and stirring at room temperature for 2 hours to obtain a mixed solution required by hydrothermal treatment.
Step (2): heating the mixed solution at 180 ℃ for 12 hours, washing and drying to obtain bismuth phosphate (marked as BiPO) 4 -1b);
And (3): prepared BiPO 4 -1b powder 20mg and 10. mu.L Nafion solution (5 wt%) were dispersed in 0.5mL of ethanol, and after ultrasonication for 60 minutes, uniformly dropped on a hydrophobic carbon paper as a working electrode (drop area 1X 1 cm) 2 ). And (3) carrying out electrolytic reduction for 60 minutes under the reduction potential of-1.1V (relative to a reversible hydrogen electrode) by taking the electrode as a working electrode, Ag/AgCl (3M KCl) as a reference electrode and a platinum mesh electrode as a counter electrode to obtain the nano flaky bismuth-based material.
Example 4
Step (1): dropwise adding a precursor solution containing 5mmol of sodium phosphate dodecahydrate into a precursor solution containing 1mmol of bismuth nitrate pentahydrate, wherein the volumes of the two solutions are 45mL and 15mL respectively (namely the concentrations of the two precursors are 0.11mol/L and 0.067mol/L respectively), and stirring at room temperature for 2 hours to obtain a mixed solution required by hydrothermal reaction.
Step (2): heating the mixed solution at 120 ℃ for 24 hours, washing and drying to obtain bismuth phosphate (marked as BiPO) 4 -1c);
And (3): prepared BiPO 4 -1c powder 50mg and 100. mu.L Nafion solution (5 wt%) dispersed in 1mL ethanol, sonicated for 60 minutes, and uniformly drop-coated on hydrophobic carbon paper as a working electrode (drop-coated area 1X 1 cm) 2 ). And (3) carrying out electrolytic reduction for 60 minutes under the reduction potential of-1.2V (relative to a reversible hydrogen electrode) by taking the electrode as a working electrode, Ag/AgCl (3M KCl) as a reference electrode and a platinum mesh electrode as a counter electrode to obtain the nano flaky bismuth-based material.
Example 5
Step (1): adding 1mmol of bismuth nitrate pentahydrate and 1mmol of ethylenediamine tetraacetic acid into 40mL of water, stirring and dissolving at 60 ℃ in water bath until the solution is clear, and obtaining a bismuth source precursor solution.
Step (2): adding 1mmol of sodium phosphate dodecahydrate into the bismuth source precursor solution, stirring for 5 minutes, then performing hydrothermal treatment at 180 ℃ for 24 hours, washing and drying to obtain bismuth phosphate (marked as BiPO) 4 -2)。
And (3): BiPO of the step (2) 4 -2 powder 10mg and 40. mu.L Nafion solution (5 wt%) dispersed in 1mL ethanol, sonicated for 30 minutes, and uniformly drop-coated on hydrophobic carbon paper as a working electrode (drop-coated area 1X 1 cm) 2 ). And (3) carrying out electrolytic reduction for 30 minutes under the reduction potential of-0.9V (relative to a reversible hydrogen electrode) by taking the electrode as a working electrode, Ag/AgCl (3M KCl) as a reference electrode and a platinum mesh electrode as a counter electrode to obtain the nano granular bismuth-based material (marked as PD-Bi2), wherein the grain diameter of the granular bismuth-based material is 50-150 nm.
Example 6
Step (1): 1mmol of bismuth nitrate pentahydrate and 1mmol of ethylenediaminetetraacetic acid were added to 40mL of nitric acid solution (275. mu.L of 65 wt% HNO 3 +40ml H 2 O) at temperatureStirring and dissolving the bismuth source precursor solution under the water bath condition of 60 ℃ until the bismuth source precursor solution is clear, thereby obtaining the bismuth source precursor solution.
Step (2): adding 1mmol sodium phosphate dodecahydrate into bismuth source precursor solution, stirring for 5 min, heating at 180 deg.C for 24 hr, washing, and drying to obtain bismuth phosphate (BiPO) 4 -3)。
And (3): BiPO of step (2) 4 -3 powders 10mg and 40. mu.L Nafion solution (5 wt%) dispersed in 1mL of ethanol, sonicated for 30 minutes, and uniformly drop-coated on hydrophobic carbon paper as a working electrode (drop-coated area 1X 1 cm) 2 ). And (3) carrying out electrolytic reduction for 30 minutes under the reduction potential of-0.9V (relative to a reversible hydrogen electrode) by taking the electrode as a working electrode, Ag/AgCl (3M KCl) as a reference electrode and a platinum mesh electrode as a counter electrode to obtain the nano flaky bismuth-based material (recorded as PD-Bi 3).
Effect example 1 oxygen atom insertion amount and microstructure characterization of bismuth-based Material
The PD-Bi electrocatalysts prepared in examples 1 and 5-6 were individually subjected to XPS testing, and the chemical states of the elements in the catalysts were investigated by XPS (ESCALAB 250Xi), and with the binding energy of the C1s peak set to 284.8eV as a reference, fig. 1a-C are the XPS spectra of the prepared PD-Bi1, PD-Bi2 and PD-Bi3 electrocatalysts, respectively, for Bi 4 f. The peak of Bi-O bond of PD-Bi1 is more intense than the peaks of PD-Bi1 and PD-Bi 2. By comparing Bi-O bonds (A) Bi-O ) Bonded to total Bi (A) Bi ) Peak area ratio (R) of (1) Bi ) To quantify the amount of O. R for PD-Bi1, PD-Bi2 and PD-Bi3 assuming that Bi is 100% bound Bi 57.1.0%, 42.4% and 38.6%, respectively, indicating that the surface of PD-Bi1 has more oxygen atoms embedded.
From the SEM images, it can be seen that PD-Bi1 and PD-Bi3 were converted into a nano-platelet structure (FIGS. 1d and 1f), while PD-Bi2 consisted of a large number of particles having an average particle diameter of 150nm dispersed on the carbon fiber (FIG. 1 e).
Effect example 2 XRD and microstructure characterization of bismuth-based Material
The XRD test (D/MAX 2550VB/PC) was performed on the PD-Bi1 electrocatalyst prepared in example 1 to determine the crystal structure. XRD pattern shows that Bi and Bi are combined 2 O 3 Corresponding diffraction peak, confirm the guaranteeBi remaining on the material 2 O 3 Presence of (figure 2 a).
The structure of the catalyst was characterized by SEM (S-3400N) and TEM (TECNAI F-30, 300 kV). Fig. 2b, 2c and 2d are SEM, TEM and HRTEM images, respectively, of PD-Bi1 prepared in example 1. BiPO can be seen from SEM and TEM 4 -1 is transformed into a nano-sheet structure (length and width of 1-10 μm, thickness of 5-15 nm) after electro-reduction. High resolution TEM showed ordered lattice fringes with pitches of 0.32nm and 0.27nm, with (012) and Bi of Bi 2 O 3 The (321) crystal plane of (A) corresponds to (B).
Effect example 3 electrocatalytic reduction of CO 2 Detection of Performance
In an H-shaped electrolytic cell separated by a Nafion115 exchange membrane, a standard three-electrode system is adopted, PD-Bi1, PD-Bi2 and PD-Bi3 are respectively used as working electrodes, Ag/AgCl (3M KCl) is used as a reference electrode, a platinum mesh electrode is used as a counter electrode, and a cathode tank is fed with 0.5M KHCO 3 Introducing CO into the electrolyte 2 To saturation, the reduction potential was then controlled to-0.8 to-1.2V (relative to the reversible hydrogen electrode) for current density testing, faradaic efficiency of formic acid, formic acid current density, impedance, Tafel curves, and double layer capacitance testing.
And (3) current density testing: in CO 2 Saturated 0.5M KHCO 3 Linear sweep voltammograms of PD-Bi1, PD-Bi2, and PD-Bi3, respectively, and 0.5M KHCO saturated in argon (Ar) were measured in solution 3 The linear sweep voltammogram of PD-Bi1 was measured in solution (FIG. 3 a). For PD-Bi1, in CO 2 The current density measured in the saturated electrolyte is greater than the current density measured in an argon (Ar) saturated electrolyte. In CO 2 In the saturated electrolyte, PD-Bi1 has a greater current density, indicating that PD-Bi1 is coupled with CO 2 The electroreduction activity of (2) is higher.
Faradaic efficiency of formic acid: as shown in FIG. 3b, a potentiostatic test was performed in the potential range of-0.8 to-1.2V, and among the three catalysts, PD-Bi1, PD-Bi2 and PD-Bi3, PD-Bi1 exhibited the most excellent Faraday efficiency of formic acid (91.4% at-0.9V); at all applied potentials, PD-Bi2 and PD-Bi3 were found to be 85% at-1.0V.
Formic acid current densityDegree: as shown in FIG. 3c, the formic acid partial current density at-1.2V of PD-Bi1 reached-17 mA cm -2 Above, it was larger than PD-Bi2 and PD-Bi3 at each potential, which indicates that CO of PD-Bi1 2 The reduction activity is higher.
Impedance, Tafel curves and double layer capacitance test: electrochemical impedance spectroscopy was performed by applying a voltage of-0.9V as shown in figure 3 d. PD-Bi1 exhibited less resistance to charge transfer, further reflecting its faster charge transfer kinetics. As shown in FIG. 3e, the slope of PD-Bi1 is lower, indicating a faster reaction rate for PD-Bi 1. FIG. 3f shows the electrochemical double layer capacitance values (C) for three catalysts, PD-Bi1, PD-Bi2 and PD-Bi3 dl ). C of PD-Bi1 catalyst dl Is 0.059mF cm -2 C of PD-Bi2 catalyst dl Is 0.052mF cm -2 And C of PD-Bi3 catalyst dl Is 0.037mF cm -2 . Thus, the larger electrochemically active area of PD-Bi1 may be electrocatalytic CO 2 Reduction provides more active sites.
Effect example 4 electrocatalytic reduction of CO 2 Performance verification of
The prepared PD-Bi1 electrocatalyst is subjected to electrochemical reduction of CO in an H-shaped electrolytic cell and a flow electrolytic cell respectively 2 And (5) testing the performance.
(1) Testing in an H-cell
Firstly, in an H-shaped electrolytic cell separated by a Nafion115 exchange membrane, a standard three-electrode system is adopted, PD-Bi1 is taken as a working electrode, Ag/AgCl (3M KCl) is taken as a reference electrode, a platinum mesh electrode is taken as a counter electrode, and the counter electrode is arranged towards a cathode groove for 0.5M KHCO 3 Introducing CO into the electrolyte 2 To saturation, and then CO is carried out by controlling the reduction potential to-0.8 to-1.2V (relative to a reversible hydrogen electrode) 2 And (4) testing reduction performance. Figure 4a is the Faradaic Efficiency (FE) and current density of different products at various potentials. The formic acid being CO 2 The only liquid phase product in the reduction is accompanied by a small amount of gas phase H 2 And CO. The faradaic efficiencies were all greater than 70% between-0.8V and-1.2V, and reached a maximum of 91.4% at-0.9V.
Next, by continuously CO at-0.9V 2 The stability of PD-Bi1 was evaluated by electroreduction for 15 hours. Followed byThe time-varying formic acid partial current density, which stabilizes approximately at-8 mA cm, is shown in FIG. 4b -2 And no obvious attenuation is generated in the test process, which indicates that PD-Bi1 has good stability.
(2) Testing in flow electrolyzers
To satisfy CO 2 The practical application of electrochemical conversion into formic acid requires that the current density is more than 200mA cm -2 . Use of flow cells to overcome CO in aqueous electrolyte in H-cell 2 Mass transfer limitations, further evaluation of electrocatalytic CO of PD-Bi1 2 Reduction performance. Loaded BiPO 4 The gas diffusion electrode of-1, porous nickel foam and saturated Ag/AgCl electrode were used as cathode, anode and reference electrode, respectively. At 50 to 200mA cm -2 The excellent performance of the PD-Bi1 electrocatalyst was demonstrated by the obtained formic acid FE over a wide range of current densities (fig. 4c and 4 d). At 200mA cm -2 At a high current density of 1.0M KHCO, the FE formate of PD-Bi1 3 And 90.5% and 90.7% in 1.0M KOH electrolyte, respectively, calculated to give the highest energy utilization efficiency of 73.0%: CO was calculated using the following formula 2 Cathode Energy Efficiency (EE) for reduction to formic acid ca ):
Wherein, E formate =-0.21V RHE Which means that CO is introduced 2 Thermodynamic potential (relative to reversible hydrogen electrode) for reduction to formic acid, FE formate Is the Faraday efficiency of formic acid, E applied Is actually applied potential (relative to a reversible hydrogen electrode) at 1M KHCO 3 And 200mA/cm in 1M KOH 2 The voltages at time were-1.26V and-0.56V (relative to the reversible hydrogen electrode), respectively, and the calculated energy use efficiencies were 52.33% and 73%, respectively. Those skilled in the art will recognize that the higher the current density, the less likely it is to maintain the energy efficiency at a higher level, whereas the current density of the present invention is at 200mA/cm 2 And the energy utilization efficiency can still reach 52.33% and 73%.
Claims (30)
1. The preparation method of the bismuth-based material is characterized by comprising the following steps: preparing bismuth phosphate into a nano bismuth-based material by an electrochemical reduction method;
the electrochemical reduction method is to prepare the bismuth phosphate into a working electrode and carry out in-situ electrochemical reduction by using a reference electrode and a counter electrode; wherein the reduction potential of the electrochemical reduction method is-0.9V to-1.2V relative to the reversible hydrogen electrode;
the mode of preparing the bismuth phosphate into the working electrode is as follows: and dispersing the bismuth phosphate and perfluorinated sulfonic acid-polytetrafluoroethylene copolymer solution in ethanol, and performing ultrasonic treatment to prepare the working electrode.
2. The method for preparing a bismuth-based material according to claim 1, wherein the bismuth phosphate is prepared by a hydrothermal method; the hydrothermal method is that a bismuth source precursor and a phosphorus source precursor are subjected to hydrothermal reaction in a hydrothermal solution;
and/or the bismuth phosphate is columnar particles, the length range of the bismuth phosphate is 200nm-2 μm, and the diameter range of the bismuth phosphate is 100nm-1 μm;
and/or the crystal structure of the bismuth phosphate is a monoclinic crystal structure.
3. The method for preparing a bismuth-based material according to claim 2, wherein the hydrothermal solution is prepared by mixing a solution of the bismuth-source precursor and a solution of the phosphorus-source precursor, or by mixing a solution of the bismuth-source precursor and the phosphorus-source precursor.
4. The method for preparing the bismuth-based material according to claim 3, wherein the hydrothermal solution is prepared by dropping the solution of the phosphorus source precursor into the solution of the bismuth source precursor and mixing.
5. The method for preparing the bismuth-based material according to any one of claims 2 to 4, wherein the bismuth-source precursor is one or more selected from the group consisting of bismuth ethylenediaminetetraacetate, bismuth nitrate and bismuth chloride;
and/or the phosphorus source precursor is sodium phosphate dodecahydrate;
and/or in the hydrothermal solution, the molar ratio of the bismuth source precursor to the phosphorus source precursor is 1: 1 to 1: 5;
and/or the concentration of the bismuth source precursor solution is 0.5-1 mol/L;
and/or the concentration of the solution of the phosphorus source precursor is 0.02-0.12 mol/L;
and/or the solvent in the hydrothermal solution is glycol and/or water.
6. The method for preparing a bismuth-based material according to claim 5, wherein the hydrothermal method is carried out according to the following steps: directly mixing the bismuth source precursor solution and the phosphorus source precursor solution to obtain the hydrothermal solution; carrying out hydrothermal reaction on the hydrothermal solution at the temperature of 160 ℃ for 4 hours; wherein the molar ratio of the bismuth source precursor to the phosphorus source precursor is 1: 1.
7. the method for producing a bismuth-based material as claimed in claim 5, wherein the bismuth source precursor is bismuth nitrate and/or bismuth chloride;
and/or in the hydrothermal solution, the molar ratio of the bismuth source precursor to the phosphorus source precursor is 1: 1 to 1: 4;
and/or the concentration of the bismuth source precursor solution is 0.67 mol/L;
and/or the concentration of the solution of the phosphorus source precursor is 0.02-0.05 mol/L.
8. The method for producing a bismuth-based material according to claim 7, wherein the bismuth source precursor is bismuth nitrate;
and/or in the hydrothermal solution, the molar ratio of the bismuth source precursor to the phosphorus source precursor is 1: 2;
and/or the concentration of the solution of the phosphorus source precursor is 0.022mol/L or 0.044 mol/L.
9. The method for preparing a bismuth-based material according to claim 8, wherein the bismuth source precursor is bismuth nitrate pentahydrate.
10. The method for producing the bismuth-based material according to any one of claims 3 to 4, wherein the mixing is stirring at room temperature; the stirring time is 5 minutes to 2 hours.
11. The method for producing a bismuth-based material according to claim 10, wherein the stirring time is 30 minutes, 1 hour or 2 hours.
12. The method for preparing the bismuth-based material according to any one of claims 2 to 4, wherein a hydrothermal temperature in the hydrothermal method is in a range of 120 to 180 ℃;
and/or the hydrothermal time in the hydrothermal process ranges from 4 to 24 hours.
13. The method for preparing a bismuth-based material according to claim 12, wherein the hydrothermal temperature in the hydrothermal method is in the range of 140 ℃ or 160 ℃;
and/or the hydrothermal time in the hydrothermal process ranges from 8 hours or 12 hours.
14. The method for producing a bismuth-based material according to claim 12, wherein the hydrothermal temperature is 160 ℃ and the hydrothermal time is 4 hours.
15. The method for producing a bismuth-based material according to claim 12, wherein the hydrothermal temperature is 140 ℃ and the hydrothermal time is 8 hours.
16. The method for producing a bismuth-based material as claimed in claim 12, wherein the hydrothermal temperature is 180 ℃ and the hydrothermal time is 12 to 24 hours.
17. The method for producing the bismuth-based material according to claim 12, wherein the hydrothermal temperature is 120 ℃ and the hydrothermal time is 24 hours.
18. The method for preparing the bismuth-based material according to claim 1, wherein the time of the electrochemical reduction method is 20 to 60 minutes.
19. The method for preparing the bismuth-based material according to claim 18, wherein the time of the electrochemical reduction method is 30 minutes.
20. The method for preparing the bismuth-based material according to claim 18 or 19, wherein the reference electrode is an Ag/AgCl reference electrode;
and/or the counter electrode is a platinum electrode.
21. The method of preparing a bismuth-based material of claim 20, wherein the solution in the Ag/AgCl reference electrode is a 3M KCl solution.
22. The method for preparing the bismuth-based material of claim 20, wherein the electrochemical reduction method comprises the steps of: dispersing the bismuth phosphate and the perfluorinated sulfonic acid-polytetrafluoroethylene copolymer solution in ethanol, performing ultrasonic treatment to prepare a working electrode, and performing in-situ electrochemical reduction by taking Ag/AgCl as a reference electrode and a platinum electrode as a counter electrode.
23. The method for preparing a bismuth-based material according to claim 20, wherein the mass concentration of the perfluorosulfonic acid-polytetrafluoroethylene copolymer solution is 5 wt%;
and/or the mass volume ratio of the bismuth phosphate to the perfluorosulfonic acid-polytetrafluoroethylene copolymer solution is 0.1-2 mg/mu L;
and/or the mass volume ratio of the bismuth phosphate to the ethanol is 1-50 mg/mL;
and/or the ultrasonic frequency of the ultrasonic is 10-50 KHz;
and/or the ultrasonic time of the ultrasonic is 20-60 minutes.
24. The method for preparing the bismuth-based material of claim 23, wherein the ultrasonic frequency is 40KHz and the ultrasonic time is 30 minutes.
25. The method for preparing a bismuth-based material according to claim 23, wherein the mass-to-volume ratio of the bismuth phosphate to the perfluorosulfonic acid-polytetrafluoroethylene copolymer solution is 0.25mg/μ L;
and/or the mass volume ratio of the bismuth phosphate to the ethanol is 1-40 mg/L.
26. The method of preparing a bismuth-based material of claim 25, wherein the mass to volume ratio of the bismuth phosphate to the ethanol is 10 mg/mL.
27. A bismuth-based material characterized by being produced by the method for producing a bismuth-based material according to any one of claims 1 to 26;
the bismuth-based material is nano-sheets or nano-particles; when the bismuth-based material is a nanosheet, the nanosheet has a length and width of 1-10 μm and a thickness of 5-15 nm; when the bismuth-based material is in the shape of nanoparticles, the particle size of the nanoparticles is 50-150 nm;
and/or the oxygen atom embedding amount of the surface of the bismuth-based material is 35-60%.
28. The bismuth-based material of claim 27, wherein the surface of the bismuth-based material has an oxygen atom insertion amount of 57.1%, 42.4%, and 38.6%.
29. The bismuth-based material of claim 28, wherein the oxygen atom insertion amount of the bismuth-based material surface is 50% to 60%.
30. The use of a bismuth-based material as claimed in any one of claims 27 to 29 for the electrocatalytic reduction of CO 2 As a catalyst.
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