CN110649274A - Porous microsphere nickel-based catalyst for enhancing direct oxidation of borohydride - Google Patents

Abstract

A porous microsphere nickel-based catalyst for enhancing direct oxidation of borohydride is characterized in that: (1) preparing 0.2mol dm under normal temperature and pressure^‑3Nickel chloride (NiCl)₂·6H₂O) and 4.5mol dm^‑3Ammonium chloride (NH)₄Cl); (2) a polished smooth 1cm multiplied by 2cm Ni sheet is used as a working electrode, a carbon strip is used as an auxiliary electrode, and a saturated calomel electrode is used as a reference electrode to assemble a three-electrode system; (3) preparing a nickel-based catalyst by adopting a pulse voltage deposition method under 298.15K, wherein the preparation conditions are as follows: high voltage of-0.3V to 0V, low voltage of-1.7V, duty ratio of 50 percent, frequency of 25mHz and deposition time of 750 s. The nickel-based catalyst prepared by the pulse voltage deposition method has the special structural appearance, and the specific surface area is obviously increased, so that the catalytic sites are increased, and the catalytic sites are reduced

The charge mass transfer resistance of direct oxidation enhances the reaction activity and improves the fuel utilization rate. Meanwhile, the special structural morphology also improves the stability of the catalyst, and obviously improves the performance of the direct borohydride fuel cell.

Description

Porous microsphere nickel-based catalyst for enhancing direct oxidation of borohydride

Technical Field

The invention belongs to the field of electrochemical application, and particularly relates to a method for preparing catalytic hydroboration radicals by a pulse voltage electrodeposition methodA direct oxidation nickel-based catalyst, and

is the negative active material of a Direct Borohydride Fuel Cell (DBFC), namely the fuel of the cell.

Background

DBFC is a group of compounds produced by direct oxidation

The chemical energy of the energy conversion device is directly converted into electric energy. Compared with the traditional hydrogen-oxygen fuel cell, the DBFC has higher cell voltage, higher specific capacity and energy conversion efficiency. In addition, the borohydride can stably exist in a solid or liquid form at normal temperature and normal pressure, so that the problems of inconvenient transportation and storage and the like of the traditional hydrogen source are avoided. Meanwhile, borohydride also belongs to a class of compounds with the highest hydrogen storage capacity, and is a good hydrogen source. However, the research in recent years finds that the method has the following problems: the catalyst is in catalysis

The hydrolysis reaction of the catalyst can be catalyzed while the catalyst is directly oxidized, so that the utilization rate of the fuel is reduced; ②

Easily penetrated septum or fixationThe body electrolyte layer and the oxidation and hydrolysis reaction occur on one side of the oxidant electrode, which not only reduces the fuel utilization rate, but also can cause the polarization on one side of the oxidant electrode to be greatly increased, thereby causing the cell voltage to be reduced and seriously affecting the performance of the DBFC. While

The direct oxidation reaction of (a) is the most important factor affecting the performance of the DBFC, which is inseparable from the anode catalyst. The current research shows that: noble metals, e.g. Pt, Pd, etc., for

Has high catalytic activity. However, the high price of noble metals severely limits the commercial development of DBFCs. In order to reduce the production cost, the same pair

The oxidation of non-noble metals Ni with catalytic capabilities has been increasingly studied. However, in the prior art, when Ni is used as the anode catalyst of DBFC, the catalytic activity is far lower than that of the noble metal catalyst, and

the hydrolysis reaction of (2) is more severe. In addition, metal Ni generates hydroxide on the surface under the alkaline condition for a long time, so that catalytic activity of catalytic sites is lost, charge mass transfer resistance of electrode reaction is increased, reaction rate is reduced, fuel utilization rate is low, and catalyst attenuation is caused. Although the non-noble metal Ni is inferior in catalytic performance to the noble metal, it has an absolute advantage in price. Therefore, the search for a non-noble metal Ni-based anode catalyst with excellent performance is an important problem to be solved urgently on the research and development path of DBFC.

Disclosure of Invention

In order to overcome a series of disadvantages mentioned above, the present invention relates to an enhancement

A porous microsphere nickel-based catalyst which is directly oxidized and has good stability. Utensil for cleaning buttockThe preparation method of the preparation is as follows:

(1) under normal temperature and pressure, 0.2mol dm is prepared^-3Nickel chloride (NiCl)₂·6H₂O) and 4.5mol dm^-3Ammonium chloride (NH)₄Cl);

(2) assembling a three-electrode system: placing a smooth Ni sheet of 1cm multiplied by 2cm as a working electrode in the solution, taking a carbon strip as a counter electrode and a saturated calomel electrode as a reference electrode;

(3) the nickel-based catalyst is prepared by adopting a pulse voltage deposition method under 298.15K, wherein the high voltage is-0.3V-0V, the low voltage is-1.7V, the duty ratio is 50%, the frequency is 25mHz, and the deposition time is 750 s.

The nickel-based catalyst prepared by adopting the pulse voltage deposition method is formed by stacking microspheres with small holes on the surface, so that the specific surface area of the catalyst is obviously increased, the catalytic active sites are greatly increased, and the number of the catalytic active sites is obviously reduced

The charge mass transfer resistance of the direct oxidation reaction is improved, thereby effectively promoting the catalysis

Activity of direct oxidation and fuel utilization; meanwhile, the stability of the catalyst is enhanced, and when the catalyst is used as a DBFC (double-walled carbon fiber) anode catalyst, the open-circuit potential, the limiting current density, the maximum power density and the like of a cell are greatly improved.

Drawings

FIG. 1 shows different nickel-based catalysts

Cyclic voltammograms of direct oxidation;

FIG. 2 XRD patterns of different nickel-based catalysts;

FIG. 3 SEM of Ni plate catalyst;

FIG. 4 PVE_0.20SEM image of catalyst;

FIG. 5 PVE_0.15SEM image of catalyst;

FIG. 6 PVE_0.10SEM image of catalyst;

FIG. 7 Ni plate catalyst action

Electrochemical impedance spectroscopy of direct oxidation;

FIG. 8 shows different nickel-based catalysts

Electrochemical impedance spectroscopy of direct oxidation;

FIG. 9 is a graph of chronoamperometry under the action of Ni pellets and different nickel-based catalysts;

FIG. 10 Ni plate and PVE_0.15Under the action of catalyst

Discharge curve of direct oxidation;

FIG. 11 is a schematic diagram of a DBFC device;

FIG. 12 polarization curves of DBFC with different catalysts;

FIG. 13 Power density curves for DBFC with different catalysts.

Detailed Description

The invention is further illustrated with reference to the following figures and examples:

example 1:

preparing 0.2mol dm under normal temperature and pressure^-3NiCl of (5)₂·6H₂O and 4.5mol dm^-3NH of (2)₄Electrodeposition bath of Cl. A polished smooth 1cm multiplied by 2cm Ni sheet is used as a working electrode, a carbon strip is used as a counter electrode, and a Saturated Calomel Electrode (SCE) is used as a reference electrode. Performing pulse voltage deposition at 298.15K, fixing low potential of-1.7V, duty ratio of 50%, frequency of 25mHz, and deposition time of 750s, and respectively preparing PVE when high potential is-0.25, -0.20, -0.15, -0.10, -0.05V_0.25、PVE_0.20、PVE_0.15、PVE_0.10、PVE_0.05And Ni flakes, totaling 6 catalysts, numbered 1 in sequence^#～6^#A catalyst.

Weighing appropriate amount of sodium borohydride (NaBH)₄) Dissolving it in 2mol dm^-3To 0.27mol dm in sodium hydroxide (NaOH) solution^-3NaBH₄The electrolyte solution of (1). The prepared nickel-based catalyst and the Ni sheet catalyst are respectively used as working electrodes, carbon strips are used as counter electrodes, Hg/HgO is used as a reference electrode, and a performance test is carried out by adopting a Cyclic Voltammetry (CV).

FIG. 1 shows the effect of 6 catalysts prepared as described above

CV curve of direct oxidation. In 1^#～6^#Under the catalysis of the catalyst, the catalyst is added,

the peak current densities of the direct oxidation are 69.7, 83.0, 195.6, 127.2, 119.6 and 20.3mAcm^-2. The oxidation peak current increases with the pulse high voltage and shows a trend of increasing and then decreasing. And, when the high voltage is-0.15V, the oxidation peak current density reaches the maximum, indicating that the catalytic activity of the nickel-based catalyst prepared at the high voltage of-0.15V is the highest. At the same time, the user can select the desired position,

the oxidation peak current density under the action of different nickel-based catalysts is far higher than that of Ni sheets, and

in PVE_0.15The oxidation peak current density under the action is nearly ten times that of the Ni plate, which shows that the pulse voltage deposition can greatly improve the metal Ni pairCatalytic activity of direct oxidation.

In conclusion, the nickel-based catalyst prepared when the pulse high voltage is-0.15V has obviously improved catalysis

Peak current density of direct oxidation and has the highestAnd (3) catalytic activity.

Example 2:

preparing 0.2mol dm under normal temperature and pressure^-3NiCl of (5)₂·6H₂O and 4.5mol dm^-3NH of (2)₄Electrodeposition bath of Cl. A polished smooth 1cm multiplied by 2cm Ni sheet is used as a working electrode, a carbon strip is used as a counter electrode, and SCE is used as a reference electrode. Performing pulse voltage deposition at 298.15K, fixing low potential of-1.7V, duty ratio of 50%, frequency of 25mHz, and deposition time of 750s, and respectively preparing PVE when high potential is-0.20, -0.15, -0.10V_0.20、PVE_0.15、PVE_0.10And Ni plate catalyst, and the 4 catalysts prepared above were subjected to X-ray diffraction test (XRD).

PVE prepared by the method when the pulse high voltage is-0.20V, -0.15V and-0.10V respectively_0.20、PVE_0.15、PVE_0.10And pure Ni pellets, for a total of 4 catalysts, were analyzed by Scanning Electron Microscopy (SEM).

FIG. 2 is X-ray diffraction spectra of different nickel-based catalysts and Ni plate catalysts, and it can be seen from the figure that XRD spectra of the catalysts are consistent with peak positions of standard diffraction card PDF #04-0850 of metallic nickel powder, which shows that the prepared nickel-based catalysts all have face-centered cubic structures. Table 1 statistics of the texture coefficients and grain sizes of the individual catalysts. As a result, it was found that when the (220) crystal plane orientation was enhanced, the oxidation peak current in CV was increased, and when the high voltage was-0.15V, the nickel-based catalyst was prepared in which the intensity of the (220) crystal plane was the strongest, the oxidation peak current corresponded the highest, and the catalytic activity was the best. In addition, the grain size of the nickel-based catalyst shows a trend that the grain size is sharply reduced at first and then gradually and slowly changed along with the increase of the pulse high voltage. When the pulse high voltage is-0.15V, the obtained grain size is far smaller than that of the Ni plate, and the catalytic activity is highest.

TABLE 1 Crystal Structure parameters of different catalysts

FIG. 3 is an SEM image of a Ni plate catalyst, from which it can be seenThe surface of the Ni sheet is relatively flat and smooth, scratches are generated by polishing, and no obvious morphological characteristics exist. This is also the reason that the specific surface area of the pure Ni sheet catalyst is small, the catalytic sites are few, and further the catalytic activity is not high. FIG. 4 is a PVE_0.20SEM image of (d). PVE_0.20The surface was uneven and a spheroidal morphology was observed after magnification. PVE compared to Ni plate catalyst_0.20Completely different surface morphologies, improves the specific surface area, increases the active sites, thereby improving the catalysis

Catalytic activity of direct oxidation. FIG. 5 is a PVE_0.15SEM image of (d). It can be seen that PVE_0.15The surface is a spherical shape which is stacked and grown, and a plurality of small holes are also arranged on each nickel microsphere. The special morphology structure greatly improves the surface area of the catalyst, increases the catalytic sites and obviously improves the catalytic activity. FIG. 6 is a PVE_0.10SEM picture of (g) shows that the surface and PVE_0.15Similarly, the porous nickel microspheres are also formed by nickel microspheres with holes on the surfaces. But the holes on the surface of the nickel microspheres are larger, and the nickel microspheres are not uniformly distributed. This is due to excessive dissolution of the deposited nickel at-0.10V, resulting in PVE_0.10Specific surface area ratio PVE_0.15And smaller, so that the catalytic activity is decreased.

In summary, PVE_0.15The catalyst, namely the nickel-based catalyst prepared when the pulse high voltage is-0.15V, has the highest diffraction peak of a (220) crystal face, smaller grain size and maximum specific surface area. Thus, to catalyze

The catalytic activity of the direct oxidation of (2) is highest.

Example 3:

preparing 0.2mol dm under normal temperature and pressure^-3NiCl of (5)₂·6H₂O and 4.5mol dm^-3NH of (2)₄Electrodeposition bath of Cl. A polished smooth 1cm multiplied by 2cm Ni sheet is used as a working electrode, a carbon strip is used as a counter electrode, and SCE is used as a reference electrode. At 298.15K, pulsed voltage deposition is carried out, wherein the low potential is fixedThe PVE is prepared respectively when the high potential is respectively-0.25, -0.20, -0.15, -0.10 and-0.05V, the duty ratio is 50 percent, the frequency is 25mHz, the deposition time is 750s_0.25、PVE_0.20、PVE_0.15、PVE_0.10、PVE_0.05And Ni pellets, for a total of 6 catalysts.

Weighing appropriate amount of NaBH₄Dissolving it in 2mol dm^-3To 0.27mol dm in NaOH solution^-3NaBH₄The electrolyte solution of (1). And (3) respectively taking the prepared nickel-based catalyst and the Ni sheet as working electrodes, taking the carbon strips as counter electrodes and taking Hg/HgO as reference electrodes to perform Electrochemical Impedance Spectroscopy (EIS) test.

FIG. 7 is

FIG. 8 is a diagram of electrochemical impedance of direct oxidation reaction under catalysis of Ni plate, and different Ni-based catalystsElectrochemical impedance spectroscopy of direct oxidation. The impedance spectrum is approximately presented as a semi-arc, the size of the diameter of the semi-arc reflects the electrode reaction charge mass transfer impedance (R)_ct) The size of (d) further reflects the ease of progress of the electrode reaction. R of each catalyst_ctRecorded in table 2. It can be seen from table 2 that the nickel-based catalysts prepared by the pulse method all have much lower resistance than the Ni sheet catalyst. This is probably because the pulse voltage deposition changes the surface morphology of the nickel coating and greatly increases the specific surface area of the catalyst, thereby significantly reducing the charge-mass transfer impedance and enabling

The direct oxidation reaction proceeds more easily. At the same time, R_ctWith the increase of the high voltage, the change rule of decreasing first and increasing second is presented, and the change rule is in PVE_0.15Under the action of R_ctAt a minimum, a 15-fold reduction compared to Ni flakes, indicating PVE_0.15Is most advantageous to

The occurrence of direct oxidation reaction effectively improves the catalysis of metallic Ni

Direct oxidation performance.

Table 2 under the action of different catalysts,

oxidized Rct and decay Rate of catalyst

Example 4:

preparing 0.2mol dm under normal temperature and pressure^-3NiCl of (5)₂·6H₂O and 4.5mol dm^-3NH of (2)₄Electrodeposition bath of Cl. A polished smooth 1cm multiplied by 2cm Ni sheet is used as a working electrode, a carbon strip is used as a counter electrode, and SCE is used as a reference electrode. Performing pulse voltage deposition at 298.15K, fixing low potential of-1.7V, duty ratio of 50%, frequency of 25mHz, and deposition time of 750s, and respectively preparing PVE when high potential is-0.25, -0.20, -0.15, -0.10, -0.05V_0.25、PVE_0.20、PVE_0.15、PVE_0.10、PVE_0.05And Ni pellet catalyst, for a total of 6 catalysts.

Weighing appropriate amount of NaBH₄Dissolving it in 2mol dm^-3To 0.27mol dm in NaOH solution^-3NaBH₄The electrolyte solution of (1). The nickel-based catalyst and the Ni sheet catalyst prepared in the above were used, 6 catalysts in total were used as working electrodes, carbon strips were used as counter electrodes, and Hg/HgO was used as a reference electrode, respectively, to perform a Chronoamperometry (CA) test.

FIG. 9 shows Ni plates and different Ni-based catalysts

Chronoamperometric profile of direct oxidation. As can be seen, all currents decay rapidly during the initial phase, and then reach a stable plateau. To compare the stability of each catalyst more quantitatively, the decay rate of each catalyst is given by the formula:

delta, attenuation rate; i is₀: an initial current value; Δ I: a current change value; Δ t: the time variation values were all 1000 s. The results of the calculations are reported in table 2. The attenuation rate of the nickel-based catalyst prepared under different high potentials is in the same level and is far smaller than that of the Ni sheet catalyst, which shows that the pulse voltage deposition can improve the corrosion resistance of metal nickel in alkali liquor, and the nickel-based catalyst prepared by the pulse voltage deposition method has better stability. In addition, it can be seen that the discharge current of each nickel-based catalyst is much larger than that of the Ni plate catalyst, and PVE_0.15The highest discharge current. At 1000s, the discharge current of the Ni plate was 4.8mA, PVE_0.15The discharge current of (A) was 157.4mA, which was about 33 times that of the Ni plate, which also indicates that the PVE_0.15The catalytic activity of the catalyst is greatly improved compared with that of the Ni sheet.

In conclusion, the stability of the nickel-based catalyst prepared by the pulse voltage deposition is far better than that of the Ni sheet catalyst, wherein the PVE_0.15In each catalyst, the discharge current was the largest and the catalytic activity was the highest.

Example 5:

preparing 0.2mol dm under normal temperature and pressure^-3NiCl of (5)₂·6H₂O and 4.5mol dm^-3NH of (2)₄Electrodeposition bath of Cl. A polished smooth 1cm multiplied by 2cm Ni sheet is used as a working electrode, a carbon strip is used as a counter electrode, and SCE is used as a reference electrode. Performing pulse voltage deposition at 298.15K, wherein the low potential of-1.7V, duty ratio of 50%, frequency of 25mHz, deposition time of 750s, and high potential of-0.15V are fixed to obtain PVE_0.15And Ni pellets amounting to 2 catalysts.

Weighing appropriate amount of NaBH₄Dissolving it in 2mol dm^-3To 0.27mol dm in NaOH solution^-3NaBH₄The electrolyte solution of (1). PVEs prepared separately as described above_0.15And Ni sheet catalyst, 2 catalysts in total are used as working electrodes, carbon strips are used as counter electrodes, Hg/HgO is used as reference electrodes, and constant current discharge (CP) test is carried out.

FIG. 10 shows that under the action of Ni plate and Ni-based catalyst,

discharge curve of direct oxidation with current density of 10mAcm^-2The volume of electrolyte was 10 mL. As can be seen from fig. 10, the Ni sheet was catalyzed by the catalyst,

the initial potential of oxidation is-0.713V and in PVE_0.15Under the catalysis of the catalyst, the catalyst is added,

the initial potential for oxidation was-1.192V, a 479mV drop over Ni plates, indicating PVE when assembled into a cell_0.15When the anode is used, higher working voltage can be obtained. In addition, in Ni flakes and PVEs_0.15Under the catalytic action of the catalyst,the discharge time of the direct oxidation reaction was 1510s and 39200s, respectively. The discharge efficiency can be calculated from the formula Q ═ It ═ nZF and η ═ t '/t, where I represents the discharge current (20mA), n represents the number of transferred electrons, 4, Z represents the amount of sodium borohydride in the electrolyte, F is the faraday constant, t represents the theoretical discharge time period, and t' represents the actual discharge time period. The discharge efficiencies of the two were calculated to be 2.90% and 75.3%, respectively. PVE_0.15The discharge efficiency is improved by 26 times compared with that of Ni plate catalyst. This is due to PVE_0.15(111) The co-preferential growth orientation of (220) and (c) promotes

The direct oxidation and the structural morphology of the nickel microspheres with pores on the surface greatly improve the surface area, increase the catalytic active sites and strengthen theThe catalytic activity improves the discharge efficiency.

In conclusion, the discharge potential and the discharge efficiency of the catalyst prepared by the pulse with the high potential of-0.15V are far better than those of the Ni sheet catalyst, and the fuel utilization rate is obviously improved.

Example 6:

preparing 0.2mol dm under normal temperature and pressure^-3NiCl of (5)₂·6H₂O and 4.5mol dm^-3NH of (2)₄Electrodeposition bath of Cl. A polished smooth 1cm multiplied by 2cm Ni sheet is used as a working electrode, a carbon strip is used as a counter electrode, and SCE is used as a reference electrode. Performing pulse voltage deposition at 298.15K, wherein the low potential of-1.7V, duty ratio of 50%, frequency of 25mHz, deposition time of 750s, and high potential of-0.15V are fixed to obtain PVE_0.15And Ni pellets amounting to 2 catalysts.

Performing performance test of direct sodium borohydride fuel cell, activating the cathode Pt electrode and setting Nafion117 film in 2mol dm^-3H₂O₂+0.5mol dm^-3H₂SO₄Boiling the mixed solution for 1H, cooling the solution to room temperature, and adding H₂Soaking in O for 2h, and then adding 0.5mol dm^-3H₂SO₄And (4) activating treatment, and finally washing with deionized water for three times to remove organic and inorganic impurities on the surface of the membrane.

0.27mol dm is prepared^-3NaBH₄+2mol dm^-3Preparing 2mol dm of NaOH anolyte^-3H₂O₂+0.5mol dm^-3H₂SO₄The catholyte solution of (1). PVEs prepared separately as described above_0.15The Ni sheet is used as an anode catalyst, the Pt electrode is used as a cathode, a Nafion117 diaphragm is assembled into the DBFC (the specific device is shown in figure 11), and a Linear Sweep Voltammetry (LSV) method is adopted for testing. In FIG. 11, A is Hg/HgO electrode, B is nickel-based catalyst anode, C is Pt sheet cathode, D is separator, E represents

Ion, F representsIon, G represents H₂O₂Molecule, H represents a water molecule.

Fig. 12 and 13 are a polarization curve and a power density curve of a DBFC under different catalysts, respectively. The electrochemical performance parameters of both catalysts are shown in table 3. The initial potential in fig. 12 corresponds to the open circuit potential of the DBFC with different catalysts as anodes. It can be seen that when PVE is used_0.15In the case of the anode, the open circuit potential of the DBFC was increased by about 150mV compared to the case of the Ni plate catalyst as the anode. While higher cell open circuit voltages tend to result in higher power densities and better cell performance. In addition, PVE is used_0.15When the nickel-based composite anode is used as a DBFC anode, the limiting current density of the battery is higher than that of a battery using a Ni sheet as an anode, and is increased by 22mAcm^-2. This is also due to PVE_0.15Catalysis

The catalytic activity of the direct oxidation is higher than that of the Ni plate catalyst. In addition, in PVE_0.15Under the action of the anode, the maximum power density of the DBFC is improved by 46.7 percent compared with that of the anode taking a Ni sheet as the anode, and reaches 51.2mW cm^-2. This can also be attributed to PVE_0.15To pair

High catalytic activity of direct oxidation, and higher open circuit potential of the cell. Therefore, when using PVE_0.15When the catalyst is an anode, the open circuit potential, the limiting current density and the maximum power density of the DBFC are greatly improved compared with those of a Ni sheet catalyst.

TABLE 3 DBFC Performance parameters for different anode catalysts

In a word, the nickel-based catalyst formed by stacking microspheres with small holes on the surface has the special morphology structure and the grain size, so that the active sites of the catalyst are greatly increased, and the catalytic activity is improved; reduceThe charge mass transfer resistance of the direct oxidation reaction enables the electrode reaction to be easier to carry out; the corrosion resistance of metal Ni in alkali liquor is enhanced, and the stability of the catalyst is improved; reduce

The discharge potential of the fuel cell obviously improves the discharge efficiency and improves the fuel utilization rate; under the action of the nickel-based catalyst, the open circuit potential, the limiting current density and the maximum power density of the DBFC are all higher than those of a Ni sheet anode catalyst, and the performance of the DBFC is obviously improved.

Claims (1)

1. A porous microsphere nickel-based catalyst for enhancing direct oxidation of borohydride is characterized by being prepared by the following method:

(1) preparing 0.2mol dm under normal temperature and pressure^-3Nickel chloride (NiCl)₂·6H₂O) and 4.5mol dm^-3Ammonium chloride (NH)₄Cl);

(2) a smooth 1cm multiplied by 2cm Ni piece is taken as a working electrode, a carbon strip is taken as an auxiliary electrode, and a saturated calomel electrode is taken as a reference electrode to assemble a three-electrode system;

(3) preparing a nickel-based catalyst by adopting a pulse voltage deposition method under 298.15K, wherein the preparation conditions are as follows: high voltage of-0.3V to 0V, low voltage of-1.7V, duty ratio of 50 percent, frequency of 25mHz and deposition time of 750 s.

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