阅读说明：本技术 铂碳纳米纤维电极及其制备方法 (Platinum carbon nanofiber electrode and preparation method thereof ) 是由 洪绍景 许永亮 李目武 秦千惠 李剑铮 蒋伟 于 2018-09-03 设计创作，主要内容包括：本发明涉及一种铂碳纳米纤维电极及其制备方法,该制备方法包括以下步骤：将碳载体、Nafion溶液及粘结剂混合,制得纺丝浆料；将所述纺丝浆料进行纺丝,得到纳米纤维催化层；将所述纳米纤维催化层转印到气体扩散层上涂有碳粉和聚四氟乙烯的表面,得到气体扩散电极；以所述气体扩散电极为工作电极,含有氯铂酸和硫酸的溶液作为电解质,采用脉冲电沉积技术,在三电极体系中在所述气体扩散电极上沉积铂纳米粒子,制得铂碳纳米纤维电极。该铂碳纳米纤维电极及其制备方法,可提高催化剂Pt的利用率和电池性能稳定性。(The invention relates to a platinum carbon nanofiber electrode and a preparation method thereof, wherein the preparation method comprises the following steps: mixing a carbon carrier, a Nafion solution and a binder to prepare spinning slurry; spinning the spinning slurry to obtain a nanofiber catalyst layer; transferring the nanofiber catalyst layer to the surface of a gas diffusion layer coated with carbon powder and polytetrafluoroethylene to obtain a gas diffusion electrode; and depositing platinum nano particles on the gas diffusion electrode in a three-electrode system by using the gas diffusion electrode as a working electrode and a solution containing chloroplatinic acid and sulfuric acid as an electrolyte by adopting a pulse electrodeposition technology to prepare the platinum-carbon nanofiber electrode. The platinum carbon nanofiber electrode and the preparation method thereof can improve the utilization rate of the catalyst Pt and the performance stability of the battery.)

1. A preparation method of a platinum carbon nanofiber electrode is characterized by comprising the following steps:

mixing a carbon carrier, a Nafion solution and a binder to prepare spinning slurry;

spinning the spinning slurry to obtain a nanofiber catalyst layer;

transferring the nanofiber catalyst layer to the surface of a gas diffusion layer coated with carbon powder and polytetrafluoroethylene to obtain a gas diffusion electrode;

and depositing platinum nano particles on the gas diffusion electrode in a three-electrode system by using the gas diffusion electrode as a working electrode and a solution containing chloroplatinic acid and sulfuric acid as an electrolyte by adopting a pulse electrodeposition technology to prepare the platinum-carbon nanofiber electrode.

2. The method according to claim 1, wherein the pulse electrodeposition current is (25 to 300) mA-cm^-2The current supply time is 0.1-2 ms, the current off time is 1.5-16 ms, and the pulse electrodeposition time is 200-3600 s.

3. The method according to claim 2, wherein the pulse electrodeposition current is (115 to 235) mA-cm^-2The current supply time is 0.8-1.2 ms, the current off time is 1.8-4 ms, and the pulse electrodeposition time is 400-1200 s.

4. The method according to claim 1, wherein the mass ratio of the carbon carrier to the solid content of the Nafion solution to the binder is 20 (6-20) to (5-10).

5. The method according to any one of claims 1 to 4, wherein the raw material of the spinning dope further comprises polytetrafluoroethylene, and the spinning dope is prepared by mixing the polytetrafluoroethylene, the carbon support, the Nafion solution, and the binder.

6. The preparation method according to claim 5, wherein the mass ratio of the polytetrafluoroethylene to the carbon carrier in the spinning slurry is (1-5): 20.

7. The method according to any one of claims 1 to 4, wherein the amount of the carbon carrier supported is (0.2 to 2.0) mg-cm^-2。

8. The method according to any one of claims 1 to 4, further comprising a step of preparing the gas diffusion layer coated with carbon powder and polytetrafluoroethylene on the surface: mixing carbon powder and 4-22 wt% of polytetrafluoroethylene slurry according to the mass ratio of 10 (0.1-5) to obtain coating slurry, blade-coating the coating slurry on the surface of carbon paper, and controlling the blade-coating thickness to be 35-250 microns to obtain the carbon paper.

9. The method according to any one of claims 1 to 4, wherein the spinning step is electrospinning at a liquid flow rate of (0.4 to 1.2) mL-h^-1The distance between the needle point and the receiving plate is (5-25) cm, the voltage is (8-22) KV, and the receiving time is (1.5-6.5) h.

10. The platinum-carbon nanofiber electrode prepared by the preparation method as set forth in any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of fuel cells, in particular to a platinum carbon nanofiber electrode and a preparation method thereof.

Background

Proton Exchange Membrane Fuel Cells (PEMFCs) have the advantages of high power density, high energy conversion efficiency, low-temperature starting, environmental friendliness, and the like, and are considered as ideal power sources for stationary power stations, electric vehicles, and portable power sources. However, successful commercialization is mainly faced with both cost and lifetime issues. In a fuel cell assembly, the cost of the catalyst accounts for nearly half, reducing the catalyst loading is the most direct way to reduce the cost of the fuel cell, and the stability of the catalyst also has an extremely important effect on the fuel cell. Therefore, the preparation process of the electrode is optimized, the utilization rate and the stability of the catalyst in the electrode are improved, and the fuel cell still has higher activity and longer service life when the Pt (platinum) loading is lower, so that the method is a preoccupation in the current low-temperature fuel cell research, and has very important practical significance for reducing the cost of the PEMFC and accelerating the commercialization process of the PEMFC. The traditional method for preparing the electrode mainly sprays or coats catalyst slurry on a proton exchange membrane or a gas diffusion layer, and has the main defects of low Pt utilization rate and unstable battery performance. Researchers adopt an electrostatic spinning technology to prepare a Pd/C nanofiber layer and then prepare an electrode in a Pt deposition mode, the utilization rate of Pt is improved, but the situation that noble metal Pd particles are coated by macromolecules and Pt cannot be deposited exists, and the utilization rate of Pd is reduced; meanwhile, the Pd nanoparticles are difficult to be completely coated by the electro-deposited Pt, the exposed Pd nanoparticles are easy to dissolve in the operating environment of the fuel cell, and the dissolved Pd has a poisoning effect on the proton exchange membrane and is not beneficial to further prolonging the service life of the fuel cell.

Disclosure of Invention

Based on the above, it is necessary to provide a platinum carbon nanofiber electrode capable of improving the utilization rate of noble metals and the stability of a battery, and a preparation method thereof.

A preparation method of a platinum carbon nanofiber electrode comprises the following steps:

mixing a carbon carrier, a Nafion solution and a binder to prepare spinning slurry;

spinning the spinning slurry to obtain a nanofiber catalyst layer;

transferring the nanofiber catalyst layer to the surface of a gas diffusion layer coated with carbon powder and polytetrafluoroethylene to obtain a gas diffusion electrode;

and depositing platinum nano particles on the gas diffusion electrode in a three-electrode system by using the gas diffusion electrode as a working electrode and a solution containing chloroplatinic acid and sulfuric acid as an electrolyte by adopting a pulse electrodeposition technology to prepare a platinum-carbon nanofiber electrode (marked as Pt @ C nanofiber electrode).

In one embodiment, the pulse electrodeposition current is (25-300) mA-cm^-2The current supply time is 0.1-2 ms, the current off time is 1.5-16 ms, and the pulse electrodeposition time is 200-3600 s.

In one embodiment, the pulse electrodeposition current is (115-235) mA-cm^-2The current supply time is 0.8-1.2 ms, the current off time is 1.8-4 ms, and the pulse electrodeposition time is 400-1200 s.

In one embodiment, the mass ratio of the carbon carrier to the solid content of the Nafion solution to the binder is 20 (6-20) to (5-10).

In one embodiment, the raw material of the spinning slurry further comprises polytetrafluoroethylene, and the polytetrafluoroethylene, the carbon carrier, the Nafion solution and the binder are mixed to obtain the spinning slurry.

In one embodiment, the mass ratio of the polytetrafluoroethylene to the carbon carrier in the spinning slurry is (1-5): 20.

In one embodiment, the carbon carrier is supported in an amount of (0.2 to 2.0) mg-cm^-2。

In one embodiment, the method further comprises a step of preparing the gas diffusion layer coated with carbon powder and polytetrafluoroethylene: mixing carbon powder and 4-22 wt% of polytetrafluoroethylene slurry according to the mass ratio of 10 (0.1-5) to obtain coating slurry, blade-coating the coating slurry on the surface of carbon paper, and controlling the blade-coating thickness to be 35-250 microns.

In one embodiment, the spinning step adopts electrostatic spinning, and the liquid flow rate of the electrostatic spinning is (0.4-1.2) mL-h^-1The distance between the needle point and the receiving plate is (5-25) cm, the voltage is (8-22) KV, and the receiving time is (1.5-6.5) h.

The platinum carbon nanofiber electrode prepared by the preparation method.

According to the platinum carbon nanofiber electrode and the preparation method thereof, the nanofiber catalyst layer is formed by adopting a spinning technology, and the network with the nanofiber structure is beneficial to improving the H proton conductivity. The C and the Nafion are uniformly dispersed on the surface of the nanofiber of the binder, so that the Pt is favorably deposited on the contact interface of the carbon carrier and the Nafion, the condition that the catalyst Pt is not in contact with the Nafion or is completely coated by the Nafion is avoided, the three-phase reaction interface of proton, electron and gas is optimized, and the utilization rate of the catalyst Pt is improved. In addition, the Pt nano particles deposited by the pulse deposition technology are irregular spheres, the average diameter is about 15nm, and the activity of the Pt catalyst is improved; meanwhile, the deposited Pt has larger grain size, which is beneficial to mass transfer, and further can improve the stability of the Pt catalyst and the battery performance.

Drawings

Fig. 1 is a scanning electron microscope image of a nanofiber catalyst layer prepared in example 1 of the present invention;

FIG. 2 is a transmission electron micrograph of a Pt @ C nanofiber electrode prepared in example 1 of the present invention;

FIG. 3 is a graph of the discharge performance of a Pt @ C nanofiber electrode made in accordance with example 1 of the present invention and a conventional electrode made in accordance with comparative example 1;

FIG. 4 is a graph of stability testing curves for Pt @ C nanofiber electrodes made according to example 1 of the present invention and for conventional electrodes made according to comparative example 1.

Detailed Description

In order that the invention may be more fully understood, a more particular description of the invention will now be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The inventor researches and discovers that the traditional electrode preparation method is mainly to spray or coat catalyst slurry on a proton exchange membrane or a gas diffusion layer, and because the uniformity of components of a carbon-supported Pt catalyst and an electrolyte in the catalyst slurry is poor, the problem that part of the carbon-supported Pt catalyst is not contacted with a Nafion membrane or part of the carbon-supported Pt catalyst is completely coated by Nafion exists after the catalyst slurry is coated, a three-phase reaction interface of proton, electron and gas cannot be effectively constructed, and the improvement of the utilization rate of Pt is not facilitated; and the electrode formed by coating is compact and not beneficial to mass transfer, so that the battery performance is not high when the Pt loading is low. The Pt @ Pd/C nanofiber electrode is prepared by scientific researchers in a mode of depositing Pt behind Pd/C nanofibers, the utilization rate of Pt is improved, but the cost of Pd is high, the utilization rate of Pd needs to be improved, and meanwhile, the risk that Pd poisons a proton exchange membrane exists.

Based on this, the invention provides a platinum carbon nanofiber electrode of an embodiment and a preparation method thereof. The preparation method comprises the following steps of S1-S4.

Step S1: and mixing the carbon carrier, the Nafion solution and the binder to prepare spinning slurry.

The carbon carrier is used as a carrier of Pt, and the Nafion solution is a perfluorosulfonic acid type polymer solution and is used for supporting an electrode; nafion and a binder are mixed, a nanofiber structure is formed through subsequent spinning, and the network of the nanofiber structure is beneficial to improving the H proton conductivity. And the C and the Nafion are uniformly dispersed on the surface of the nanofiber of the binder, so that the subsequent deposition of Pt on the contact interface of the carbon carrier and the Nafion is facilitated, the condition that the catalyst Pt is not in contact with the Nafion or is completely coated by the Nafion is avoided, the three-phase reaction interface of proton, electron and gas is optimized, and the utilization rate of the catalyst Pt is improved.

In one embodiment, the loading amount of the carbon carrier is (0.2-2.0) mg-cm^-2。

Preferably, the binder is at least one of polyacrylic acid, polyacrylonitrile and polyvinylpyrrolidone. These binders are soluble in at least one of isopropanol and water, and the binders may be dissolved in at least one of isopropanol and water to form a solution, which is added to the spinning dope in the form of a binder solution. Specifically, the mass content of the binder solution is 8-15%.

In one embodiment, the mass content of the Nafion solution is 3% -9%, and the mass ratio of the carbon carrier, the Nafion solution and the binder is 20 (6-20) to 5-10. Preferably, the mass ratio of the carbon carrier, the Nafion solution and the binder is 20 (15-20) to (5-10).

In one embodiment, the raw material of the spinning slurry also comprises polytetrafluoroethylene, and the spinning slurry is prepared by mixing the polytetrafluoroethylene, a carbon carrier, a Nafion solution and a binder. The inventor finds that the polytetrafluoroethylene is added into the spinning slurry, so that the hydrophobicity of the prepared nanofiber catalyst layer is favorably improved. Preferably, the mass ratio of the polytetrafluoroethylene to the carbon carrier in the spinning slurry is (1-5): 20.

Preferably, in the step S1, ultrasonic treatment is adopted for 2 to 4 hours, and then stirring is carried out for 18 to 40 hours.

Step S2: and spinning the spinning slurry to obtain the nanofiber catalyst layer.

The nanofiber catalyst layer prepared in step S2 has a nanofiber structure, and the average diameter of the fibers is 250 μm. C and Nafion are uniformly dispersed on the surface of the nano-fiber of the binder, so that the utilization rate of the catalyst Pt is improved.

In one embodiment, the spinning step adopts electrostatic spinning, and the liquid flow rate of the electrostatic spinning is (0.4-1.2) mL.h^-1The distance between the needle point and the receiving plate is (5-25) cm, the voltage is (8-22) KV, and the receiving time is (1.5-6.5) h.

Step S3: and transferring the nanofiber catalyst layer to the surface of a Gas Diffusion Layer (GDL) coated with carbon powder and polytetrafluoroethylene to obtain the gas diffusion electrode.

The main function of the gas diffusion layer in the gas diffusion electrode is to allow the reactant gases to pass smoothly and to supply the reactive layer with the gases required for the corresponding reaction. The nanofiber catalyst layer is a place where a reduction reaction of oxygen occurs, and the gas delivered from the gas diffusion layer forms an electrochemical reaction activation point together with a catalyst and an electrolyte therein, thereby reducing the reaction gas.

In one embodiment, the method further comprises the step of preparing the gas diffusion layer coated with carbon powder and polytetrafluoroethylene: mixing carbon powder and 4-22 wt% of polytetrafluoroethylene slurry according to the mass ratio of 10 (0.1-5) to obtain coating slurry, blade-coating the coating slurry on the surface of the carbon paper, and controlling the blade-coating thickness to be 35-250 microns.

The transfer printing step can adopt a hot pressing method for transfer printing, the hot pressing pressure of the transfer printing is (0.25-1) MPa, the time is 1-5 min, and the hot pressing temperature is 135-142 ℃. Preferably, the hot pressing pressure of the transfer printing is (0.25-0.5) MPa, the time is 3-4 min, and the hot pressing temperature is 139-141 ℃.

Step S4: the platinum carbon nanofiber electrode is prepared by depositing platinum nanoparticles on a gas diffusion electrode in a three-electrode system by using a pulse electrodeposition technology and taking the gas diffusion electrode as a working electrode and a solution containing chloroplatinic acid and sulfuric acid as an electrolyte.

Specifically, a saturated calomel electrode can be used as a reference electrode, a graphite electrode can be used as a counter electrode, and a solution of chloroplatinic acid and sulfuric acid can be used as an electrolyte.

Step S4 is to deposit Pt on the gas diffusion electrode by using a pulse electrodeposition technique, where the Pt is deposited at the interface where the carbon carrier and the proton conductor Nafion contact, so as to avoid the situation that the catalyst Pt is not in contact with Nafion or is completely coated by Nafion, optimize the three-phase reaction interface of proton, electron and gas, and improve the utilization rate of the catalyst Pt. In addition, the deposited Pt nano particles are in irregular spherical shapes, the average diameter is about 15nm, and the activity of the Pt catalyst is improved; meanwhile, the deposited Pt has larger grain size, which is beneficial to mass transfer and improves the stability of the Pt catalyst.

In one embodiment, the pulse electrodeposition current is (25-300) mA-cm^-2The current supply time is 0.1-2 ms, the current off time is 1.5-16 ms, and the pulse electrodeposition time is 200-3600 s.

Preferably, the current of the pulse electrodeposition is (115-235) mA-cm^-2The current supply time is 0.8-1.2 ms, the current off time is 1.8-4 ms, and the pulse electrodeposition time is 400-1200 s.

In the electrolyte, the concentration of chloroplatinic acid is (0.1-60) mmol/L, and the concentration of sulfuric acid is (0.1-2) mol/L.

According to the platinum-carbon nanofiber electrode and the preparation method thereof, the nanofiber catalyst layer is formed by adopting a spinning technology, the gas diffusion electrode is formed by transfer printing, and then the catalyst Pt is deposited by adopting a pulse deposition technology. Therefore, the condition that the catalyst Pt is not contacted with Nafion or is completely coated by Nafion is avoided, the three-phase reaction interface of proton, electron and gas is optimized, and the utilization rate of the catalyst Pt is improved; the deposited Pt nano particles are irregular spheres, the average diameter is about 15nm, and the activity of the Pt catalyst is improved; meanwhile, the deposited Pt has larger grain size, which is beneficial to mass transfer, and further can improve the stability of the Pt catalyst and the battery performance.

In addition, the carbon carrier without the metal catalyst is adopted, so that the problem of low utilization rate caused by coating of the catalyst by Nafion in the step S1 can be further avoided, and the problem of instability of the Nafion membrane caused by degradation of the Nafion membrane by adopting a Pd catalyst is avoided by adopting a pulse deposition technology to deposit the catalyst Pt in the step S4, so that the utilization rate of the catalyst and the stability of the performance of the battery are improved.

The structure of the prepared platinum carbon nanofiber electrode is as follows: a nanofiber catalyst layer is formed on the gas diffusion layer coated with carbon powder and polytetrafluoroethylene on the surface, and a catalyst Pt is deposited on the nanofiber catalyst layer. The nanofiber catalyst layer has a nanofiber structure, the average diameter of the fibers is 250 microns, and C and Nafion are uniformly dispersed on the surface of the nanofiber of the binder; pt is deposited at the contact interface of the carbon carrier and the proton conductor Nafion, and the deposited Pt nano particles are in an irregular spherical shape and have an average diameter of about 15 nm.

Furthermore, the Pt content of the prepared platinum-carbon nanofiber electrode is (0.03-0.4) mg-cm^-2. The Pt has larger grain size and is beneficial to mass transfer, so the battery performance is still excellent when the Pt loading is lower, and the stability of the Pt catalyst is improved.

The following are specific examples.