CN107342425A - The preparation of bifunctional catalyst diatomite confinement cobalt platinum based composites and its application in electrocatalytic oxidation reduction and oxygen evolution reaction - Google Patents

Abstract

The invention discloses the preparation of a diatomite (DTM) confined cobalt-platinum-based composite material (CoPt-x/DTM-C) prepared by a simple method and its electrocatalytic application. The advantages of this invention are: (1) The preparation method is simple: firstly, the pores of DTM are used to adsorb Pt ⁴⁺ and Co ²⁺ ions, and then the Pt ⁴⁺ and Co ²⁺ ions are reduced. (2) High catalytic activity: In the oxygen reduction reaction, the mass activity and specific activity of the composite are 2.5 and 1.5 times that of CoPt‑x/C, and 4.6 and 2.2 times that of platinum carbon. In the oxygen evolution reaction, the overpotential of CoPt‑x/DTM‑C is 30mV lower than that of CoPt‑x/C; (3) Low cost: the catalyst has a low Pt content and a wide range of sources of diatomite, which greatly reduces the The cost of the catalyst has good prospects for commercial application.

Description

Preparation of diatomite-confined cobalt-platinum-based composites as bifunctional catalysts and their application in electrocatalysis Applications in Oxygen Reduction and Oxygen Evolution Reactions

technical field

The confined cobalt-platinum alloy nanomaterial prepared by the invention is applied to electrocatalytic oxygen reduction and oxygen evolution reaction, and belongs to the field of new energy materials. It specifically relates to the preparation of nano-catalysts and their applications in metal-air batteries and proton exchange membrane fuel cells.

Background technique

New energy conversion and storage devices are an effective way to solve current energy and environmental problems. Fuel cells have attracted widespread attention from society for their high energy conversion efficiency, environmental friendliness, and portability. Proton exchange membrane fuel cells have the advantages of clean and pollution-free, low working temperature, fast start-up, simple structure and convenient operation. power supply. The oxidation of hydrogen fuel occurs at the anode, and the reduction of oxygen occurs at the cathode. Both electrodes contain catalysts that accelerate the electrochemical reaction of the electrodes. However, the low reaction rate of the cathode is the main bottleneck restricting the commercial development of fuel cells. At present, the cathodic oxygen reduction catalyst is mainly based on platinum-based noble metal materials, but its activity and stability cannot meet the needs of fuel cell development. In addition, platinum is a noble metal with limited earth crust content and high cost. Therefore, improving the activity and stability of platinum-based catalysts and reducing the amount of platinum used are the main directions of research on cathode oxygen reduction catalysts. A metal-air battery is a type of fuel cell, and its reaction equation is: Negative pole: M-xe ^- = M ^{x +} ; Positive pole: O ₂ -xe ^- = x/2O ^2- (equation 1)

It can be seen from the reaction equation (1) that the metal at the negative electrode of the metal-air battery loses electrons, and _O2 on the positive electrode gains electrons. Anode materials are generally elements with high crustal content such as metal Zn and Al. As we all know, the preparation technology of Zn and Al metal elements is mature, and metals such as Zn and Al are easy to lose electrons in the electrolyte, so the anode material is not a constraint for metal-air batteries. main factor of development. On the contrary, the reduction of _O2 at the positive end is much more difficult than the oxidation of Zn and Al metals, and requires the assistance of a catalyst, and the higher the concentration of _O2 in the electrolyte, the better the performance of the battery. This requires the anode material to have two basic properties: (1) the performance of catalyzing the reduction of oxygen; (2) the performance of catalyzing the oxygen production of the electrolyte. The current metal-air battery cathode materials are expensive, the manufacturing process is cumbersome, and the catalytic stability is poor, which restricts the commercial development of metal-air batteries. Therefore, cheap, efficient and simple preparation process of bifunctional catalysts is the key to promote the further development of metal-air batteries.

Alloy nanomaterials composed of Pt-based noble metals and transition metals M (M=Fe, Co, Ni, Mn, Cu, etc.) have greatly improved oxygen reduction performance, but their performance decays too fast, which affects the performance of fuel cells. commercial use. The use of diatomite-confined alloy nanoparticles can inhibit the attenuation of catalyst activity to a certain extent and improve the long-term stability of the catalyst.

Oxygen evolution catalysts are currently dominated by noble metal oxides such as RuO ₂ and IrO ₂ , transition metal oxides such as Fe, Co, and Ni, transition metal hydroxides, and carbon materials, but RuO ₂ and IrO ₂ noble metal oxides are expensive and have poor stability Although transition metal oxides and hydroxides and carbon materials have reduced costs, their performance and stability still cannot meet the needs of the development of metal-air batteries. PtCo-x/DTM-C has good catalytic activity for oxygen reduction and oxygen evolution, and low Pt content, abundant DTM resources, low cost, and has good application prospects in the development of metal-air batteries.

Fuel cell cathode catalysts are generally platinum-based noble metal materials, which are expensive to manufacture and used in large quantities. Therefore, the cost of the cathode catalyst is a major factor in the high price of fuel cells. The PtCo-x/DTM-C catalyst has a low Pt content and uses diatomite to confine metal nanoparticles. Its activity and stability have been improved, and the synthesis conditions are mild and the method is simple, which has the prospect of industrial production.

The preparation of the diatomite-confined cobalt-platinum-based composite material used in the present invention and its application in electrocatalytic oxygen reduction and oxygen evolution reactions have not yet been published in literature or patent reports.

Contents of the invention

The preparation method of diatomite-confined cobalt-platinum-based composite material as a bifunctional catalyst is used in electrocatalytic oxygen reduction and oxygen evolution reactions.

The present invention is achieved through the following technical solutions, specifically comprising the following steps:

(1) Disperse diatomaceous earth into 40mL of 3mol L ^-1 HCl solution, stir well for 12h, then suction filter, wash with deionized water until the filtrate pH ~ 7, dry the filter cake in a vacuum oven at 50°C, the product Marked as DTM spare.

(2) Control the molar ratio of Co and Pt to be Co/Pt=1, Co/Pt=3 and Co/Pt=9, and the precursor salts of Co and Pt CoCl ₂ ·6H ₂ O and H ₂ PtCl ₆ ·6H ₂ O was added to 20mL EG solution, after the precursor salt was completely dissolved, 76mg DTM was added, and after magnetic stirring for 30min, it was heated from room temperature to 160°C for 6h.

(3) When the reaction temperature dropped to 40°C, 76 mg of carbon powder was added, magnetically stirred for 4 hours, washed by centrifugation, and dried at 50°C under vacuum for 12 hours.

(4) The prepared catalyst was coated on a glassy carbon working electrode with a loading capacity of 80.8ug cm ^-2 , and the oxygen reduction test condition was tested under rotating conditions in an oxygen-saturated 0.1mol L ^-1 KOH electrolyte, The oxygen evolution reaction is a 1molL ^-1 KOH solution saturated with N ₂ , and the test temperature is room temperature.

The DTM used in the step (1) is to confine the CoPt nanoparticles and inhibit the agglomeration of the nanoparticles during the reaction, thereby maintaining the activity of the catalyst.

The EG used in step (2) is a reducing agent and a solvent, which can reduce Pt ⁺⁴ and Co ⁺² at a temperature of 160°C, and can also diffuse Pt ⁺⁴ and Co ⁺² into the pores of DTM.

The carbon powder added in step (3) is to protect the diatomite so that it is not easy to be etched by the electrolyte during the reaction. The carbon powder can also promote the transfer rate of the charge on the catalyst material, and strengthen the catalyst CoPt and the catalytic substrate. charge transfer between them.

The purpose of using the rotating disk electrode in step (4) is to speed up the diffusion of _O2 on the electrode and to characterize the catalytic performance of the material itself more truly.

In summary, compared with the prior art, the present invention is superior in that:

(1) The preparation method of the present invention is simple, does not require calcination, avoids pollution and energy consumption caused by calcination, is environmentally friendly and energy-saving, and simplifies the synthesis process.

(2) The synthesized CoPt-x/DTM-C catalyst, the CoPt nano-catalyst is confined in the DTM channel, has greater catalytic activity in the process of oxygen reduction and oxygen generation, and the tolerance has also been significantly improved.

( ₃ ) The onset potential and half _- wave potential of the catalyst synthesized by this method are superior to commercial Pt/C in the oxygen reduction reaction, and the limiting current density, electron transfer number and H2O2 yield are also comparable to commercial Pt/C , and the stability is far superior to that of commercial Pt/C, which provides an efficient dual-function catalyst for fuel cells and metal-air batteries, and has good application prospects.

Description of drawings

Figure 1a, b, and c are the transmission electron microscopy (TEM) analyzes of the CoPt-9/DTM-C catalyst at different magnifications, respectively.

Figure 2 is the X-ray diffraction patterns of CoPt-9/DTM-C and CoPt-9/C.

Figure 3 and Figure 4 are the nitrogen adsorption-desorption isotherm profiles of DTM and CoPt-9/DTM-C, respectively, and the inserts are the corresponding pore size distributions.

Figure 5 is the X-ray photoelectron diffraction patterns of CoPt-9/DTM-C and CoPt-9/C.

Figure 6 shows the polarization curves of CoPt-1/DTM-C, CoPt-3/DTM-C, CoPt-9/DTM-C and Pt/DTM-C in _O2 saturated 0.1mol L ^-1 KOH solution .

Figure 7 shows the polarization curves of CoPt-1/DTM-C, CoPt-1/C and Pt/C in O ₂ saturated 0.1mol L ^-1 KOH solution.

Figure 8 shows the polarization curves of the CoPt-1/DTM-C electrode in _O2 -saturated 0.1mol L ^-1 KOH solution at different rotation speeds.

Figure 9 shows the number of electrons transferred and the yield of hydrogen peroxide when CoPt-1/DTM-C catalyzes oxygen reduction in O ₂ -saturated 0.1 mol L ^-1 KOH solution.

Figure 10 shows the polarization curves of CoPt-9/DTM-C and CoPt-9/C in nitrogen-saturated 1mol L ^-1 KOH solution.

Fig. 11 shows the Tafel curves and their slopes of CoPt-9/DTM-C, CoPt-9/C, Co/DTM-C and Co/C.

Figure 12 is a comparison of the oxygen reduction stability of CoPt-1/DTM-C and CoPt-1/C.

Figure 13 is a comparison of the oxygen evolution stability of CoPt-9/DTM-C and CoPt-9/-C.

detailed description

Below in conjunction with example the present invention is further described, but the present invention is not limited to following examples.

Example 1.

(1) Disperse diatomaceous earth into 40 mL of 3 mol L ^-1 HCl solution, stir magnetically for 12 h, then suction filter, wash with deionized water until the filtrate pH ~ 7, and dry the filter cake in a vacuum oven at 50 ° C for 12 h, The product is marked as DTM for future use.

(2) Control the molar ratio of Co and Pt to Co/Pt=1, add the precursor salt of Co and Pt 0.25mmol CoCl ₂ ·6H ₂ O and 0.25mol H ₂ PtCl ₆ ·6H ₂ O to 20mL EG solution After the precursor salt is completely dissolved, add 76mg of DTM, stir for 30min, then start heating from room temperature to 160°C for 6h.

(3) When the reaction temperature drops to 40°C, add 76 mg of carbon powder, stir for 4 hours, and wash by centrifugation. CoPt-1/DTM-C catalyst can be obtained by drying at 50℃ for 12h under vacuum condition.

Electrochemical performance test:

The electrochemical test and characterization was performed on the CHI 750E electrochemical workstation produced by Shanghai Chenhua Company. The three-electrode system was used for testing. The platinum sheet was used as the counter electrode, the Ag/AgCl electrode was used as the reference electrode, and the glassy carbon electrode loaded with catalyst was used as the working electrode. . Weigh 2 mg of the catalyst into 1.0 mL of ethanol solution, add 10 μL of Nafion dropwise to prepare a standard solution, and sonicate the mixture for 30 minutes to obtain a catalyst suspension with a concentration of 2 mg/mL. 10 μL of the catalyst suspension was evenly spread on the glassy carbon electrode and dried naturally in the air to obtain a catalyst loading of 80.8 μg/cm ² . During the oxygen reduction performance test, the working electrode was placed in an oxygen-saturated 0.1M KOH solution for the voltammetric cycle characteristic test, and the oxygen evolution performance test was carried out in a N ₂ saturated 1M KOH solution. The structure and performance characterization are shown in the figure.

Figure 1 Transmission electron microscope shows that CoPt alloy nanoparticles are attached to diatomaceous earth and carbon support. The high magnification image (c) shows that there are two different lattice fringes in the nanoparticles, and the distances are with Represent the (111) crystal plane and (200) crystal plane of the PtCo alloy, respectively, which correspond to the X-ray diffraction pattern in Figure 2. It can be observed in Figure 2 that the crystal form of the CoPt alloy does not change before and after adding diatomite, and the (111), (200) and (220) crystals of CoPt appear at 2theta of 40.1°, 46.2° and 68.2° respectively. On the surface, it shows that the CoPt alloy nanoparticles have a face cubic (FCC) structure. At the same time, the amorphous diffraction peak of diatomite also appeared at 21.9°.

The _N2 -adsorption-desorption isotherm graphs in Fig. 3 and Fig. 4 show that the curves of DTM and CoPt-9/DTM-C belong to the typical IV-type curves, and it can be seen from the insert that the pore size distribution of diatomite is between 10- Between 30nm and within 10nm, the pore size also has a distribution, and after adding CoPt and carbon powder, the pore size is mainly distributed around 6nm and 13nm, so CoPt nanoparticles and carbon powder reduce the pore size of diatomite. It is proved that nanoparticles can be synthesized in diatomaceous earth, and XC-72 particles can also be well filled into the pores, thereby increasing the electron transport ability of CoPt alloy and catalytic substrate.

Figure 5 X-ray photoelectron diffraction shows that the addition of diatomaceous earth changes the binding energy of CoPt. It can be seen from the figure that the binding energy of Pt 4f _7/2 shifts positively by 14eV when diatomite is added. Studies have shown that the Fermi level With the reduction of binding energy, the reduction of Fermi energy level will weaken the chemical adsorption bond energy, so that the oxygen-containing species adsorbed on the surface of CoPt will be more easily broken under the catalysis of CoPt, thus promoting the material to oxygen. catalytic performance.

Figure 6 is the polarization curve of the oxygen reduction reaction. With the catalyst prepared in this example, the initial potential gradually shifts negatively with the increase of Co content. It can be seen from the figure that the initial potential of CoPt-1 is about 1.0V, while that of CoPt- 9 at around 0.95V.

Figure 7 shows that the onset potential of CoPt-1/C catalyst is 0.94V, which is about 40mV higher than that of CoPt-1/DTM-C, and the overpotential of CoPt-1/DTM-C is about 10mV lower than that of Pt/C. The current density of Pt/C at 0.4V (vs.RHE) is 4.8mA cm ^-2 , while the current density of CoPt-1/DTM-C reaches 5.4mA cm ^-2 at the same voltage, and CoPt-1/C is 4.7mA cm ^-2 . It shows that the addition of diatomite not only promotes the initial potential of the material but also increases the limiting diffusion current.

Figure 8 is the K-L curve corresponding to the oxygen reduction performance of CoPt-1/DTM-C. It can be seen from the figure that the current at different rotation rates shows a good linear relationship, indicating that the reaction is an ideal first-order reaction process.

Figure 9 shows the number of electron transfers and the yield of by-product hydrogen peroxide when CoPt-1/DTM-C catalyzes the oxygen reduction reaction. It can be seen from the figure that the number of electron transfers increases from 3.85 to 3.92 after adding diatomaceous earth, and the yield of hydrogen peroxide It also dropped from an average of 5.5% to around 4.5%.

The performance curve of the catalyst prepared in this example in the oxygen evolution reaction is shown in Figure 10, the overpotential of CoPt-9/DTM-C at a current density of 10mA cm ^-2 is 380mV and that of CoPt-9/C is 410mV, The addition of diatomaceous earth reduces the overpotential of CoPt-9 catalyst by about 30mV, and the overpotential of Co/DTM-C is also reduced by about 25mV compared with Co/C, so diatomite also improves the oxygen evolution performance of the catalyst. The Tafel curves characterize the kinetic properties of CoPt-9/DTM-C, CoPt-9/C, Co/DTM-C and Co/C. It can be seen from Figure 11 that the corresponding slopes are 120mV dec ^-1 , 136mV dec ^-1 , 132mV dec ^-1 and 137mVdec ^-1 , where the slope of CoPt-1/DTM-C is 16mV dec ^-1 lower than that of CoPt-1/C, Co/DTM-C is also 5mV dec ^-1 lower than that of Co/C , indicating that the addition of diatomite promotes the catalytic performance of the material dynamically.

Figure 12 and Figure 13 are the corresponding stability tests. It can be seen from the figure that the oxygen reduction stability of the material increases from 81% of CoPt-1/C to 95% of CoPt-1/DTM-C after adding diatomaceous earth. The oxygen stability increased from 81.6% of CoPt-9/C to 93.4% of CoPt-9/DTM-C. These results prove that diatomaceous earth does protect the CoPt nanoparticles during the catalytic reaction and enhance the long-term stability of the catalyst.

Example 2.

(1) Disperse diatomaceous earth into 40 mL of 3 mol L ^-1 HCl solution, stir magnetically for 12 h, then suction filter, wash with deionized water until the filtrate pH ~ 7, and dry the filter cake in a vacuum oven at 50 ° C for 12 h, The product is marked as DTM for future use.

(2) Control the molar ratio of Co and Pt to Co/Pt=3, add Co and Pt precursor salts 0.75mmol CoCl ₂ ·6H ₂ O and 0.25mol H ₂ PtCl ₆ ·6H ₂ O to 20mL EG solution After the precursor salt is completely dissolved, add 76mg of DTM, stir for 30min, then start heating from room temperature to 160°C for 6h.

(3) When the reaction temperature dropped to 40°C, 76 mg of carbon powder was added, stirred for 4 hours, and washed by centrifugation. CoPt-3/DTM-C catalyst can be obtained by drying at 50℃ for 12h under vacuum condition.

Example 3.

(1) Disperse diatomaceous earth into 40 mL of 3 mol L ^-1 HCl solution, stir magnetically for 12 h, then suction filter, wash with deionized water until the filtrate pH ~ 7, and dry the filter cake in a vacuum oven at 50 ° C for 12 h, The product is marked as DTM for future use.

(2) Control the molar ratio of Co and Pt to Co/Pt=9, add the precursor salt of Co and Pt 2.25mmol CoCl ₂ ·6H ₂ O and 0.25mol H ₂ PtCl ₆ ·6H ₂ O to 20mL EG solution After the precursor salt is completely dissolved, add 76mg of DTM, stir for 30min, then start heating from room temperature to 160°C for 6h.

(3) When the reaction temperature dropped to 40°C, 76 mg of carbon powder was added, stirred for 4 hours, and washed by centrifugation. CoPt-9/DTM-C catalyst can be obtained by drying at 50℃ for 12h under vacuum condition.

The electrochemical testing method of example 2,3 is identical with example 1. The test results are shown in the figure. The catalyst prepared in Example 1 has the best performance as an oxygen reduction catalyst, with an initial potential of 1.1 V, a half-wave potential of 0.88 V, a limiting current density of 5.5 mA cm ^-2 , and an electron transfer number n of 3.8 to 3.9, the yield of H ₂ O ₂ is 2.2%~10%; the onset potential of Pt/C is 0.98V, the half-wave potential is 0.75V, the limiting current density is 5.8mA cm ^-2 , and the electron transfer number n is 3.88~ 3.94, and the yield of H ₂ O ₂ was 4.8%-5.5%. Its onset potential and half-wave potential are higher than those of commercial Pt/C, and its limit power density, electron transfer number and H ₂ O ₂ yield are also comparable to those of commercial Pt/C, and its stability is also very good. CoPt-9/DTM-C has the best oxygen evolution performance, and its overpotential at 10mAcm ^-2 current density is 380mV. Compared with CoPt-9/C, it can be explained that the addition of diatomite greatly promotes the Oxygen evolution catalyst performance.

The above-mentioned embodiment is a preferred specific implementation of the present invention, but the scope of protection of the present invention is not limited thereto, and any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention, All should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (5)

1. the preparation of bifunctional catalyst diatomite confinement cobalt platinum based composites and its electrocatalytic oxidation reduction and oxygen evolution reaction In application, it is characterised in that：Comprise the following steps：

(1) diatomite is distributed in HCl solution, is sufficiently stirred certain time, then filters, be washed with deionized to filtrate PH~7, filter cake is dried in vacuum drying oven, Product Labeling is that DTM is standby.

(2) Co and Pt mol ratio is controlled, Co and Pt precursor salt is added in EG solution, treats that precursor salt is completely dissolved After add DTM, after stirring certain time, begin to warm up.

(3) carbon dust, stirring a period of time, centrifuge washing, vacuum drying are added after dropping at the reaction temperatures.

(4) prepared catalyst series are applied in electrocatalytic oxidation reduction and oxygen evolution reaction.

2. the preparation of the bifunctional catalyst diatomite confinement cobalt platinum based composites described in claim 1 and its in electrocatalytic oxidation Application in reduction and oxygen evolution reaction, it is characterised in that：HCl concentration used in step (1) is 3mol L^-1, volume 40mL, It is to remove the impurity in diatomite with the HCl purposes handled.

3. the preparation of the bifunctional catalyst diatomite confinement cobalt platinum based composites described in claim 1 and its in electrocatalytic oxidation Application in reduction and oxygen evolution reaction, it is characterised in that：Co and Pt mol ratio is Co/Pt=1, Co/Pt=3 in step (2) And Co/Pt=9, the precursor salt in step (2) is H₂PtCl₆·6H₂O and CoCl₂·6H₂O, the EG volumes added are 20mL, DTM quality are 76mg, and the heating-up temperature described in step (2) is 160 DEG C, mixing time 6h.

4. the preparation of the bifunctional catalyst diatomite confinement cobalt platinum based composites described in claim 1 and its in electrocatalytic oxidation Application in reduction and oxygen evolution reaction, it is characterised in that：Step (3) temperature drops to 40 DEG C, and the quality of added carbon dust is 76mg, Mixing time is 4h.

5. the preparation of the bifunctional catalyst diatomite confinement cobalt platinum based composites described in claim 1 and its in electrocatalytic oxidation Application in reduction and oxygen evolution reaction, it is characterised in that：Step (4) test condition is：Prepared catalyst coated is taken in glass On carbon working electrode, its carrying capacity is 80.8 μ g cm^-2, hydrogen reduction test environment is the 0.1mol L of oxygen saturation^-1KOH electrolyte Tested under middle rotating condition, oxygen evolution reaction is in N₂The 1mol L of saturation^-1In KOH solution.All tests are all carried out at room temperature.