A method for preparing a hydrogen energy catalyst with a high-efficiency mass transfer three-phase interface

Abstract

The application relates to a preparation method of a hydrogen energy catalyst with a high-efficiency mass transfer three-phase interface, which comprises the following steps: (1) taking a commercial Pt / C, PtM / C (M is an excessive metal) catalyst as the basis, mixing the catalyst with concentrated H2SO4 and concentrated HNO3 solutions through sufficient stirring, achieving carboxyl treatment on the surface of the carbon carrier of the catalyst, and thus forming DNA grafting sites; (2) stirring the customized DNA and the catalyst subjected to the carboxyl treatment in step (1) at a selected temperature, so that the end groups of the DNA are stably combined with the carboxyl groups on the surface of the carbon carrier; (3) mixing the catalyst grafted with the DNA with a metal ion solution of a selected element; and (4) removing the DNA residues through acid treatment, finally forming metal nanotube arrays with a self-supporting function on the surface of the carbon carrier of the catalyst, and completing the preparation of the catalyst. The method can solve the problems of the prior art, such as the limited material transmission at the Pt-ionomer interface, the activity reduction caused by the sulfonic acid group poisoning and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel cells, and particularly relates to a preparation method of a hydrogen energy catalyst with a high-efficiency mass transfer three-phase interface. BACKGROUND

[0002] Reduction of the cathode Pt loading is the key to realize cost reduction and commercialization of the proton exchange membrane fuel cell system; however, it is found that reduction of the cathode Pt loading will cause an increase in the oxygen transmission flux per unit Pt surface area at a large current, an increase in the transmission impedance of oxygen at the Pt-ionomer interface, and a decrease in the performance of the battery. Therefore, improvement of the oxygen transmission at the Pt-ionomer interface is the key to improve the performance output of the low-Pt cathode catalyst layer fuel cell at a large current condition.

[0003] At present, in the preparation of the membrane electrode, direct mixing of the catalyst and the ionomer inevitably causes coating of the ionomer on the Pt. This not only causes a decrease in the oxygen transmission efficiency of the Pt surface, but also causes densification of the fluorine skeleton in the ionomer film on the Pt surface, blockage of the water transmission channel in the ionomer film, and a decrease in the proton transmission efficiency; in addition, the sulfonic acid group in the coating state is easy to be adsorbed on the Pt, causing a decrease in the ORR active site. Therefore, under the condition of guaranteeing efficient proton transmission, controllable separation of the Pt and the ionomer and elimination of the coating of the ionomer on the Pt are the fundamental way to improve the oxygen transmission capacity of the Pt surface, reduce the poisoning effect of the sulfonic acid group on the Pt, and improve the utilization rate of the Pt metal. However, there is no related report. Similar to the proton exchange membrane fuel cell, the supported catalyst in the proton exchange membrane water electrolysis also has the problem of coating of the ionomer on the catalyst in the preparation process of the membrane electrode, and a series of problems caused by the coating. Therefore, under the condition of guaranteeing efficient proton transmission, controllable separation of the catalyst particles (such as IrO 2, SnO2, etc.) and the ionomer is also the fundamental way to improve the utilization efficiency of the catalyst in the proton exchange membrane water electrolysis. SUMMARY

[0004] Based on the above technical problems, the application provides a preparation technology of a hydrogen energy catalyst with a high-efficiency mass transfer three-phase interface. The technology can realize controllable separation of the catalyst particle-ionomer interface structure, thereby improving the oxygen transmission efficiency of the catalyst particle surface, reducing the poisoning effect of the sulfonic acid group on the catalyst particle, improving the water transmission and proton transmission between the catalyst particle and the ionomer film, reducing the poisoning effect of the sulfonic acid group on the catalyst particle, and improving the electrochemical activity of the catalyst; meanwhile, the high reducibility and low oxidation potential of the formed metal nanotube can adsorb and reduce the dissolved Pt ions, restore the Pt activity, inhibit the oxidation and dissolution of the Pt under a high potential and a potential cycle condition, enhance the durability of the catalyst, and finally realize double improvement of the performance and the service life of the catalyst.

[0005] Specifically, the technical solutions adopted by the present application are as follows:

[0006] A hydrogen energy catalyst preparation method with a high-efficiency mass transfer three-phase interface, comprising the following steps:

[0007] (1) Based on a commercial catalyst, the catalyst is fully stirred and mixed with concentrated H2SO4 and concentrated HNO3 solution to realize carboxylation treatment of the carbon carrier surface of the catalyst, so that carboxyl functional groups are evenly attached to the carbon carrier surface to form DNA grafting sites;

[0008] (2) The customized DNA is fully stirred with the catalyst subjected to the carboxylation treatment in step (1) at a selected temperature, so that the end groups of the DNA are stably combined with the carboxyl groups on the carbon carrier surface to realize directional grafting of the DNA on the carbon carrier;

[0009] (3) The catalyst grafted with the DNA is fully mixed with a metal ion solution of a selected element to complete metallization of the DNA;

[0010] (4) Through acid treatment, the DNA residues are removed, and finally a metal nanotube array with a self-supporting function is formed on the carbon carrier surface of the catalyst, and the catalyst preparation with a self-supporting catalyst-metal nanotube array-ionomer interface structure is completed.

[0011] Preferably, in step (1), the commercial catalyst particles include but are not limited to Pt / C, PtM / C (M is an excessive metal) catalyst, non-noble metal catalyst and supported water electrolysis catalyst such as IrO2, SnO2, RuIrO x , etc.

[0012] Preferably, in step (1), the carbon carrier of the Pt / C catalyst or PtM / C catalyst includes but is not limited to solid carbon, porous carbon, mesoporous carbon and other fuel cell catalyst carriers and tin dioxide, titanium dioxide and other supported water electrolysis catalyst carriers.

[0013] Preferably, in step (1), the carboxylation is not limited to the existing catalyst, but also includes the process of integrating step (1) into the preparation process of the catalyst from a precursor solution; in this process, the precursor solution includes but is not limited to chloroplatinic acid, chloroiridic acid, etc.; the preparation process includes but is not limited to the polyol reduction method, the impregnation method, etc.

[0014] Preferably, in step (1), the catalyst carbon carrier or other carrier treatment includes but is not limited to carboxylation treatment, epoxy modification treatment, carbonyl modification treatment, hydroxylation modification treatment, etc.; the formed surface functional groups include but are not limited to carboxyl, epoxy, carbonyl, hydroxyl, etc.; the reagents used for the acid treatment of the carbon carrier or other carrier surface include but are not limited to H2SO4, HNO3, aldehyde, ketone, acid anhydride, etc.

[0015] Preferably, in step (2), the DNA includes but is not limited to single-stranded DNA, double-stranded DNA, and related templates obtained by DNA origami technology.

[0016] Preferably, in step (2), the DNA end group is combined with the carbon carrier surface related group in the form of, but not limited to, covalent bond, chemical absorption, etc.

[0017] Preferably, in step (2), the DNA combined with the carbon carrier in the form of site includes but is not limited to the combination of DNA end base with the carbon carrier or other carrier surface functional group, the combination of DNA skeleton (with negative charge) with the carbon carrier surface or catalytic particle surface through electrostatic adsorption, etc.

[0018] Preferably, in step (3), the metal ion solution of the selected element includes but is not limited to Au, Ti, etc. The metal ion solution that can exist stably in the electrocatalytic reaction environment after reduction to form metal nanotubes, and also includes organic or inorganic matter with certain supporting stiffness and conductive properties, etc.

[0019] Preferably, in step (4), the method for removing DNA residues includes but is not limited to acid treatment, high temperature treatment, etc. Treatment methods; or no treatment process measures.

[0020] Preferably, in step (4), the supporting structure finally formed on the surface of the carbon carrier or other carrier includes but is not limited to microstructures such as metal nanotube array, nanowire array, whisker, etc. With or without self-supporting function, vertical or non-vertical to the surface of the carbon carrier to realize the controllable separation of Pt-ionomer interface structure.

[0021] Compared with the prior art, the beneficial technical effects of the present application are as follows:

[0022] In the prior art, the direct mixing of catalyst and ionomer in the process of preparing membrane electrode inevitably causes the coating of ionomer on Pt. This not only causes the reduction of oxygen transmission efficiency on the surface of Pt, but also causes the densification of fluorine skeleton in the ionomer film on the surface of Pt, the water transmission channel in the film is blocked, and the proton transmission efficiency is reduced; in addition, the sulfonic acid group in the coated state is easy to be adsorbed with the catalytic particles, causing the reduction of active sites. In order to optimize the interface structure of the catalytic particle-ionomer, the prior art improves the oxygen transmission at the interface by modifying the ionomer and the carbon carrier, but in this method, the Pt particles are still coated in the ionomer, and the influence of Pt on the densification of the microstructure in the ionomer film and the poisoning effect of the sulfonic acid group of the ionomer on the Pt particles are still not fundamentally solved. The use of mesoporous carbon effectively protects the Pt catalytic particles loaded in the mesoporous carbon, but the Pt particles loaded on the surface of carbon still have the problem of ionomer coating; in addition, considering the durability, mesoporous carbon is mainly used in passenger cars, while commercial vehicles mainly use solid carbon carriers with higher structural stability, so the strategy of improving the Pt-ionomer interface material transmission by using mesoporous structure has certain limitations for commercial vehicle catalysts. Compared with the above, the present application constructs a catalytic particle-ionomer interface structure with self-supporting function, adjustable control of isolated space, and long-term stable existence under the condition of guaranteeing efficient proton transmission channel, which not only improves the material transmission at the interface of fuel cell or proton exchange membrane water electrolysis catalyst particles and ionomer, but also eliminates the poisoning effect of ionomer on catalytic particles, improves the catalytic activity and utilization efficiency; at the same time, the high reducibility and low oxidation potential of the metal nanotube formed can adsorb and reduce the dissolved Pt ions on one hand, restore the Pt activity; on the other hand, it can also inhibit the oxidation and dissolution of Pt under high potential and potential cycle conditions, enhance the durability of the catalyst, and finally realize the dual improvement of catalyst performance and service life.

[0023] In order to optimize the interface structure of the catalytic particle-ionomer, the prior art introduces the sulfonated organic metal framework (SDT-COFs) after sulfonation, which not only ensures the rapid proton conduction in the channel, but also better solves the problem of microstructure densification in the Nafion film caused by coating and the problem of sulfonic acid group poisoning, but the sheet structure of the COFs used is relatively small compared with the size of the Pt particles and does not have a self-supporting function, and the space regulation ability of the Pt-ionomer interface is weak. In addition, the space isolation structure between the Pt particles and the COFs has the risk of being coated by the ionomer as a whole. At the same time, the random distribution of the COFs in the catalyst / ionomer solution may also exist in the case that part of the Pt particles are not coated and supported by the COFs. In addition, the COFs also have the problems of hydrolysis and temperature stability, which may affect the long-term effectiveness of the structure. Compared with the prior art, the metal elements with good chemical stability, such as gold (Au) and titanium (Ti), which have higher reduction than Pt, are selected as the metalized ions of DNA, which not only ensures the stability of the metal nanotube array structure, but also can adsorb and reduce the aged and dissolved Pt ions, and restore the Pt activity. In addition, the nanotubes after acid treatment have strong hydrophilicity, which can well adsorb the product water on the Pt surface or the water in the ionomer film to form water injection metal nanotubes; by using the electrostatic effect between the electric charge on the metal surface of the nanotube and the protons in the water, the structure not only can ensure the efficient proton transmission efficiency at the interface to be constructed, but also can improve the water transmission efficiency between the catalyst surface and the ionomer under the effects of electroosmosis and reverse diffusion.

[0024] In addition, the present application also has the advantages of simple process, good repeatability, controllable preparation process conditions, controllable interface structure, significantly reduced raw material cost, and suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The cyclic voltammetry test curve of the catalyst prepared in Example 1.

[0026] Figure 2 The cycle life curve of the catalyst prepared in Example 1.

[0027] Figure 3 The polarization performance test of the catalyst membrane electrode prepared in Example 1.

[0028] Figure 4 The cyclic voltammetry test curve of the catalyst prepared in Example 2.

[0029] Figure 5 The cycle life curve of the catalyst prepared in Example 2.

[0030] Figure 6 The polarization performance test of the catalyst membrane electrode prepared in Example 2. DETAILED DESCRIPTION

[0031] The following describes one embodiment of the present disclosure in detail, but the present disclosure is not limited thereto.

[0032] Example 1

[0033] (1) Mix 50 mg of Pt / C catalyst with 45 mL of concentrated H2SO4 and 15 mL of concentrated HNO3. Then heat the mixture to 50 °C and stir continuously for 5 hours to complete the carboxylation treatment of the carbon support surface of Pt / C catalyst, so that the carboxyl functional groups are sufficiently and uniformly attached to the carbon support surface, thereby forming DNA grafting sites;

[0034] (2) Mix 8.75 μL of DNA fragment with a length of 3-5 nm with 10.0 mL of biological grade ultrapure water without any buffer, add 1.00 g of carboxylated Pt / C catalyst prepared in step (1), stir continuously for 1 hour, and then freeze overnight at -20°C. The next morning, thaw the frozen suspension and wash it with a large amount of ultrapure water.

[0035] (3) The Pt / C solution with DNA anchored on its surface obtained in step (2) was mixed with 20 mL of deionized water containing 92 mg AuCl4. The mixture was vigorously mixed overnight with stirring, and then the mixture was freeze-dried to remove moisture to obtain Pt / C-metal nanotube array catalyst powder.

[0036] (4) The Pt / C-metal nanotube array catalyst powder obtained in step (3) was stirred and washed with H2SO4 solution at pH=1 for 5h, and then dried. The resulting solid powder was washed three times with deionized water and dried in an oven at 80 degrees for 12h to obtain the Pt / C-metal nanotube array catalyst (Pt / C-MNTs).

[0037] Example 2

[0038] 60 mg of PtCo / C catalyst was mixed with 45 mL of concentrated H2SO4 and 15 mL of concentrated HNO3. The mixture was then heated to 50 °C and stirred continuously for 5 hours to complete the carboxylation treatment of the PtCo / C catalyst carbon support surface, so that the carboxyl functional groups were sufficiently and uniformly attached to the carbon support surface, thereby forming DNA grafting sites.

[0039] (1) Mix 8.75 μL of DNA fragment with a length of 3-5 nm with 10.0 mL of biological grade ultrapure water without any buffer, add 1.00 g of carboxylated PtCo / C catalyst prepared in step (1), stir continuously for 1 hour, and then freeze overnight at -20 °C. The next morning, thaw the frozen suspension and wash it with a large amount of ultrapure water.

[0040] (2) The PtCo / C solution with DNA anchored on the surface prepared in step (2) was mixed with 20 mL of deionized water solution containing 92 mg of AuCl4under stirring overnight. The mixture solution was then freeze-dried to remove water to obtain PtCo / C-metal nanotube array catalyst powder.

[0041] (3) The PtCo / C-metal nanotube array catalyst powder prepared in step (3) was washed with a H2SO4solution with pH = 1 under stirring for 5 h, and then dried. The obtained solid powder was washed with deionized water for three times and dried in an 80-degree oven for 12 h to obtain PtCo / C-metal nanotube array catalyst (PtCo / C-MNTs).

[0042] Figure 1 is the cyclic voltammetry test curve of the catalyst prepared in Example 1. The electrochemical active area (ECSA) of the catalyst prepared in Example 1 is 73.4 m2 / g, which is 21.1 m2 / g higher than that of the original commercial Pt / C catalyst (ECSA = 52.3 m2 / g). This is because the self-supported metal nanotube array on the surface of the catalyst prepared in Example 1 separates Pt from the ionomer, eliminates the poisoning effect of the ionomer on Pt, increases the number of active sites of the catalyst, and thus makes the electrochemical area of the catalyst higher. On the other hand, the presence of the self-supported metal nanotube array on the surface of the catalyst particles can also alleviate the problem of Pt coverage and reduction of available Pt caused by agglomeration of Pt / C particles during slurry preparation, so as to increase the ECSA of the catalyst clusters. Therefore, the catalyst as a whole has a higher active area.

[0043] Figure 2 is the cyclic voltammetry test curve of the catalyst prepared in Example 1 after 15000 cycles, and the ECSA is 65.8 m2 / g, which is 10.4% lower than the initial performance. The ECSA of the commercial Pt / C after 15000 cycles is 41.8 m2 / g, which is 20.1% lower than the initial performance, which is higher than that of the catalyst prepared in Example 1. This is mainly because the self-supported metal nanotube array on the surface of the catalyst prepared in Example 1 has a higher reduction and a lower oxidation potential relative to Pt. On the one hand, it can adsorb and reduce dissolved Pt ions to restore Pt activity. On the other hand, it can also inhibit the oxidation and dissolution of Pt at high potential and potential cycling conditions. At the same time, the metal nanotube array also has a certain confinement effect on Pt particles, so it exhibits higher durability.

[0044] Figure 3The polarization curve of the catalyst prepared in Example 1 is compared with the polarization curve of the original commercial Pt / C catalyst. The catalyst prepared in Example 1 has higher voltage in the large current area, which reflects better mass transfer characteristics. This is mainly due to the separation of the Pt and ionomer interface, which improves the oxygen transfer efficiency on the surface of the catalytic particles, improves the water transfer and proton transfer between the Pt-ionomer membrane, and thus reduces the concentration polarization caused by mass transfer, thereby improving the performance of the membrane electrode at a large current. At the same time, the catalyst prepared in Example 1 also shows higher voltage in the lower current range, which is mainly due to the separation of the Pt and ionomer interface, which eliminates the poisoning of the ionomer to Pt and alleviates the problem of Pt coverage and reduction of available Pt caused by agglomeration, thereby making the catalyst prepared in Example 1 have higher electrochemical activity, lower electrochemical polarization voltage, and improved performance of the membrane electrode.

[0045] Figure 4 The cyclic voltammetry test curve of the catalyst prepared in Example 1 is shown. The electrochemical active area (ECSA) of the catalyst prepared in Example 2 is 81.3 m2 / g, which is 19.9 m2 / g higher than that of the original commercial PtCo / C catalyst (ECSA = 61.4 m2 / g). This is due to the separation of Pt and ionomer on the surface of the self-supported metal nanotube array of the catalyst prepared in Example 2, which eliminates the poisoning of the ionomer to PtCo, increases the number of active sites of the catalyst, and thus makes the electrochemical area of the catalyst higher. On the other hand, the presence of the self-supported metal nanotube array on the surface of the catalyst particles can also alleviate the problem of PtCo coverage and reduction of available PtCo caused by agglomeration during slurry preparation, which increases the ECSA of the catalyst clusters. Thus, the catalyst as a whole has a higher active area.

[0046] Figure 5 The cyclic voltammetry test curve of the catalyst prepared in Example 2 after 15000 cycles is shown. The ECSA is 73.7 m2 / g, which is 9.3% lower than the initial performance. The ECSA of the commercial PtCo / C after 15000 cycles is 48.8 m2 / g, which is 20.5% lower than the initial performance, which is higher than that of the catalyst prepared in Example 2. This is mainly due to the self-supported metal nanotube array on the surface of the catalyst prepared in Example 2, which has higher reducibility and lower oxidation potential than PtCo. This can adsorb and reduce dissolved Pt ions, restore Pt activity, and inhibit the oxidation and dissolution of Pt at high potential and potential cycling conditions. At the same time, the metal nanotube array has a certain confinement effect on the PtCo particles, so it has higher durability.

[0047] Figure 6The polarization curve prepared in Example 2 is compared with the polarization curve of the original commercial PtCo / C catalyst, and the catalyst prepared in Example 2 has higher voltage in the large current area, which reflects better mass transfer characteristics. This is mainly due to the separation of the PtCo and ionomer interface, which improves the oxygen transfer efficiency on the surface of the catalytic particles, improves the water transfer and proton transfer between the PtCo-ionomer membrane, and thus reduces the concentration polarization caused by mass transfer, thereby improving the performance of the membrane electrode under large current. At the same time, in the lower current range, the catalyst prepared in Example 1 also shows higher voltage, which is mainly due to the separation of the PtCo and ionomer interface, which eliminates the poisoning of the ionomer to PtCo, and alleviates the problem of PtCo coverage and reduction of available PtCo caused by agglomeration, thereby making the catalyst prepared in Example 2 have higher electrochemical activity, lower electrochemical polarization voltage, and improved performance of the membrane electrode.

[0048] The catalyst of the present application has good mass transfer characteristics, higher catalytic activity and good durability, and is mainly applied to fuel cells, water electrolysis catalysts and other new energy fields.

[0049] This embodiment is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims of the present application.

Claims

1. A method for preparing a hydrogen energy catalyst with a highly efficient mass transfer three-phase interface, comprising the following steps: (1) Based on commercial catalysts, the catalyst is thoroughly mixed with concentrated H2SO4 and concentrated HNO3 solutions to achieve carboxylation treatment on the surface of the catalyst carbon support, so that the carboxyl functional groups are sufficiently and uniformly attached to the surface of the carbon support, thereby forming DNA grafting sites. (2) Mix the customized DNA with biological-grade ultrapure water, and then stir it thoroughly with the catalyst after carboxylation treatment in step (1) at the selected temperature. After freezing overnight, thaw it to make the DNA terminal groups and the carboxyl groups on the carbon support surface stably bonded, so as to realize the directional grafting of DNA on the carbon support. (3) The DNA-grafted catalyst is thoroughly mixed with a metal ion solution of a selected element and freeze-dried to complete the metallization of DNA. The metal ion solution is an aqueous solution of AuCl4. (4) DNA residue is removed by acid treatment, and a self-supporting metal nanotube array is finally formed on the surface of the catalyst carbon support, thus completing the preparation of a catalyst with a self-supporting catalyst-metal nanotube array-ionomer interface structure.

2. The preparation method according to claim 1, wherein in step (1): the commercial catalyst comprises: Pt / C catalyst, PtM / C catalyst: M is a transition metal, non-noble metal catalyst, IrO2 supported water electrolysis catalyst, or RuIrO x Supported water electrolysis catalyst.

3. The preparation method according to claim 2, wherein in step (1): the carbon support of the Pt / C catalyst or PtM / C catalyst comprises: Supports for solid carbon and porous carbon fuel cell catalysts.

4. The preparation method according to claim 1, wherein in step (1): the surface treatment of the catalyst carbon support, in addition to carboxylation treatment, further includes: Epoxy modification, carbonyl modification, or hydroxylation modification; The surface functional groups formed include: carboxyl, epoxy, carbonyl, or hydroxyl groups.

5. The preparation method according to claim 1, in step (2): the DNA comprises: Single-stranded DNA, double-stranded DNA, and related templates obtained through DNA origami technology, wherein the DNA terminal groups bind to related groups on the carbon support surface in the form of covalent bonds.

6. The preparation method according to claim 1, wherein in step (2): the DNA-carbon carrier binding form includes: DNA terminal bases bind to functional groups on the carbon support surface, while negatively charged DNA backbones bind to the carbon support surface or catalytic particle surface through electrostatic adsorption.

7. The preparation method according to claim 1, wherein in step (4), the method for removing DNA residue includes: Acid treatment, high temperature treatment.

8. The preparation method according to claim 1, wherein in step (4), the final formation on the surface of the catalyst carbon support comprises: Metal nanotube arrays, nanowire arrays, or whisker microstructures that are self-supporting and perpendicular or non-perpendicular to the carbon support surface.

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