CN100464841C - A kind of noble metal electrocatalyst based on nano carbon fiber and preparation method thereof - Google Patents

Abstract

The invention discloses a nano-carbon fiber-based noble metal electrocatalyst and a preparation method thereof. Based on the unique physical and chemical properties of nano-carbon fibers, the present invention utilizes the advantages of electrochemical deposition and chemical deposition methods, abandons the shortcomings of electrochemical deposition and chemical deposition methods, and achieves the characteristics of small particles of precious metals, uniform dispersion, and strong interaction with the carrier. . The nano-carbon fiber-based noble metal dot catalyst prepared by the invention has the characteristics of high noble metal loading capacity, small particles, uniform dispersion, high electrocatalyst activity, and the like.

Description

A kind of noble metal electrocatalyst based on nano carbon fiber and preparation method thereof

technical field

The invention relates to a noble metal electrocatalyst based on nano-carbon fiber and a preparation method thereof. The electrocatalyst can be applied to a fuel cell, especially to a proton exchange membrane fuel cell (PEMFC), and belongs to the technical field of electrocatalysis and energy conversion.

Background technique

A fuel cell is a device that directly converts the chemical energy of fuel (such as hydrogen, methanol, ethanol) and oxidant (such as oxygen, air) into electrical energy. Due to the advantages of energy conversion not limited by the Carnot cycle and environmental friendliness, fuel cells have become the focus of attention in academia and industry. Proton exchange membrane fuel cells have the advantages of high energy conversion efficiency, clean and pollution-free, and have become the focus of mobile power research. However, despite nearly half a century of research, proton exchange membrane fuel cells are still at the stage of laboratory research. The main reason for this is the limitation of electrocatalyst performance. Generally speaking, Pt and other noble metal catalysts are generally used as electrocatalysts for proton exchange membrane fuel cells. Due to the high price of Pt group metals, the price of electrocatalysts is relatively high. Meanwhile, the utilization rate of electrocatalysts is low, usually only 10–30 wt%. In order to improve the overall performance of electrocatalysts, it is common practice to support noble metals such as Pt on activated carbon supports to increase the metal dispersion, thereby reducing the amount of electrocatalysts used. For example, by loading Pt on activated carbon, the amount of Pt can be reduced from the initial 9 mg/cm ² to 0.4 mg/cm ² . At the same time, many researchers are also trying to reduce the cost of fuel cells by synthesizing new non-precious metal catalysts (Holze R, Vielstich WJ Electrochem Soc 131(10): 2298-2303; Arai H, Muller S, Haas O. J Electrochem Soc 147(16):3584-91.), but little progress has been made in this area, and the purpose of replacing noble metal catalysts cannot be achieved. In recent years, the research focus of fuel cell electrocatalysts has shifted to the improvement of support materials and preparation methods. USP4054687 reported a method for obtaining a high specific surface area Pt/C electrocatalyst by high temperature graphitization treatment of carrier carbon black. At the same time, many researchers pay attention to carbon nanotubes with excellent physical and chemical properties as electrocatalyst supports, and the electrocatalysis based on carbon nanotubes also shows good electrochemical performance (J.Wang, M.Musameh, Y.Lin, J. .Am.Chem.Soc.125(2003)2408; Y.Lin, W.Yantasee, J.Wang, Front.Biosci.10(2005)492; Y.Lin, F.Lu, Y.Tu, Z.Ren , Nano Lett.4(2004) 191; Y.Lin, F.Lu, J.Wang, Electroanalysis 16(2004) 145; M.Musameh, J.Wang, A.Merkoci, Y.Lin, Electrochem.Commun.4 (2002) 743.). However, as an electrocatalyst carrier, carbon nanotubes also have their own shortcomings. For example, the specific surface area of carbon nanotubes is small, generally only tens of m ³ /g. At the same time, the structure of carbon nanotubes is relatively regular, and the interaction with the loaded metal is weak, which is not conducive to the loading and dispersion of the noble metal, and is also not conducive to the electron exchange between the loaded noble metal and the carrier.

Carbon Nanofiber (Carbon Nanofiber) can better overcome the shortcomings of traditional carrier materials. Carbon nanofibers include plate carbon nanofibers, herringbone carbon nanofibers and tubular carbon nanofibers. Carbon nanofibers have the advantages of large specific surface area, unique mesopore size distribution, good mechanical properties and excellent electrical conductivity (H.Dai, Surf.Sci.500 (2002) 218.M.Ledoux, R.Vieira, C. Pham-Huu, N.Keller, J.Catal.216(2003)33; K.P.De Jong, J.W.Geus, Catal.Rev.-Sci.Eng.42(2000)481; N.M.Rodriguez, J.Mater.Res.8 (1993)3233.), becoming the focus of research on electrocatalyst supports. Most importantly, carbon nanofibers have microstructure controllability, and the microstructure of carbon nanofibers can be adjusted by controlling the preparation parameters, thereby achieving the ability to control the surface properties of carbon nanofibers and the ability to position, disperse and interact with carriers.

At present, the loading methods of noble metal electrocatalysts mainly include chemical methods represented by deposition-precipitation method and gel-sol method, and electrochemical deposition methods represented by potentiostatic deposition and underpotential deposition. The deposition precipitation method is mainly to disperse the carrier uniformly in the solvent, select a certain precious metal precursor, impregnate it into the carrier (such as carbon black), then adjust it to a suitable pH value, and drop a reducing agent at a certain temperature to obtain the required load. type metal electrocatalysts. There are many studies on this method, but because the deposition precipitation method has the characteristics of complex preparation process, long cycle, poor control of the particle size and poor dispersion of the prepared noble metal, many researchers are trying to use other loading methods.

The sol-gel method is a better choice. The sol-gel method mainly includes two steps (Joel Le Bars, Ullrich Specht, John S. Bradley, Donna G. Blackmond, Langmuir 1999, 15, 7621-7625; Jason A. Widegren, John D. Aiken, III, Saim O Zkar, Richard G. Finke, Chem. Mater. 2001, 13, 312-324; Arnim Henglein, J. Phys. Chem. B, Vol. 104, No. 29, 2000.). First of all, using precious metal catalyst metal compound as raw material, adding a certain stabilizer such as polyethylene glycol, orthosilicate, polyvinylpyridine, polyvinyl alcohol, sodium citrate, trioctyl phosphine, etc. and reducing agent such as hydrogen , ethanol, acetaldehyde, hydrazine, carbon monoxide, hydroxylamine, silane, borohydride, etc., followed by a hydrolysis reaction to transform the metal compound in the solution into a stable colloid containing the metal or the metal oxide. Then the sol is prepared into a catalyst by gel sintering, hydrothermal, microwave treatment and other methods. Compared with the traditional deposition-precipitation method, the sol-gel method has the characteristics of simple process, small particle size and high dispersion of the prepared noble metal catalyst. However, due to the extremely uncontrollable sol process, the prepared noble metal particles grow up, which affects the catalytic performance of the electrocatalyst.

Electrochemical deposition has also attracted the attention of many researchers. Electrochemical deposition is to place the noble metal precursor in the electrolyte, use the prepared catalyst carrier electrode as the working electrode, and directly deposit the noble metal catalyst by electrochemical method. The method has the characteristics of simplicity, convenience and high utilization rate of precious metals. However, due to the existence of a certain overpotential in the deposition process, and because the traditional electrochemical deposition process will make the particle size of the loaded metal grow all the time, the obtained noble metal particles are generally large, which is not conducive to obtaining high loading capacity, high dispersion and small particle size. the goal of.

In the conventional preparation process of supported noble metal electrocatalysts, the noble metals are generally supported on the support material to obtain the electrocatalyst, and then the required electrocatalyst electrode is obtained by bonding and bonding the electrocatalyst and the binder through a certain method. In practical applications, only half of the noble metal electrocatalysts are in contact with the reactants, which severely reduces the utilization of the electrocatalysts.

Contents of the invention

The invention provides a brand-new noble metal electrocatalyst based on nano-carbon fiber and a preparation method. The invention has the characteristics of simple method, short electrocatalyst preparation period, simple route and the like. At the same time, the electrocatalyst prepared by this method has the advantages of small noble metal particle size, uniform dispersion and high utilization rate.

The present invention is achieved through the following technical solutions:

A noble metal electrocatalyst based on carbon nanofibers, characterized in that: noble metals are uniformly dispersed on the carbon nanofiber carrier, the content of noble metals in the electrocatalyst is 5-30wt%, and the particle size of noble metals is between 2-6nm.

Wherein, the carbon nanofibers are plate-type carbon nanofibers, herringbone-type carbon nanofibers and tube-type carbon nanofibers with a diameter of 1-200nm,

Said precious metals include one or more of Pt, Pd and Ru metals.

A preparation of a noble metal electrocatalyst based on carbon nanofibers comprises the following steps:

(1) Purification and activation of carbon nanofibers

a) Wash the carbon nanofibers with 4M NaOH at 80°C for 2 hours, filter and wash again until the pH value is equal to 7.0, and then dry them in a drying oven at 120°C; step a) is repeated 4 times;

b) The carbon nanofibers obtained after repeating step a) 4 times were placed in a 2M HCl solution at 60°C for 4 hours, then filtered and washed until the pH value was equal to 7.0, and then dried in a drying oven at 120°C, Step b) repeat 3 times;

c) oxidize the carbon nanofibers obtained after repeating step b) 3 times in an air atmosphere at 250° C. for 6 hours, extract with absolute ethanol for 12 hours after the treatment, and then vacuum-dry and set aside for use;

(2) Preparation of carbon nanofiber electrodes

Mix the purified and activated carbon nanofibers with the bonding material at normal temperature to prepare carbon nanofiber electrodes, the content of the bonding material accounts for 1-99% of the total mass of the carbon nanofibers and the bonding material, preferably 5-50wt%, especially 10-30wt%,

Wherein: said bonding material is selected from the polytetrafluoroethylene solution of 1-80% by mass percentage, the polyethylene glycol of 100% purity, epoxy resin and the Nafion solution of 2-30% by mass percentage A sort of,

Said Nafion solution is produced by Dupont Corp., serial number: CASReg.No.31175-20-9;

(3) Preparation of noble metal catalyst sol

Take the noble metal precursor, form a noble metal solution with a mass percentage of 0.1% to 25% by adding HCl, NH ₃ , NaOH or absolute ethanol with a mass percentage of 1% to 30%, and then add an appropriate amount of The mass percentage is the stabilizer solution of 0.1%-10%, and NaOH solution is added simultaneously, until the pH of gained solution is greater than 12; After that, at a heating rate of 10°C/10min, raise the temperature to 110°C and keep it for 3 hours; then, cool down to 80°C and keep it stable for 30 minutes, then slowly add 1M HCl dropwise to adjust the pH of the solution to 3, and keep it stable for 10 minutes; finally , add a small amount of reducing agent and keep it at 80°C for 2 hours to obtain the required precious metal sol;

Wherein, said stabilizer comprises: one in the solution of polyethylene glycol, orthosilicate, polyvinylpyridine, polyvinyl alcohol, sodium citrate, trioctyl phosphine,

Said reducing agent includes: one of hydrogen, ethanol, acetaldehyde, hydrazine, carbon monoxide, polyethylene glycol, and PVP (polyvinylpyrrolidone) with a mass percentage of 10% to 100%;

(4) Preparation of noble metal electrocatalysts based on carbon nanofibers

At room temperature, place the prepared carbon nanofiber electrode in the noble metal catalyst sol prepared in step (3), and use the corresponding noble metal electrode as a counter electrode to perform electrochemical deposition within the range of ±0.50V relative to the equilibrium potential. The temperature is 0-80°C, preferably 10-60°C, preferably 20-50°C, the deposition time is related to the required load and overpotential, generally 0-60min, preferably 5-30min, and then the obtained nano The carbon fiber noble metal electrocatalyst electrode is washed with ultrapure water until the pH value is 7.0, and then dried in an Ar atmosphere at 40-50°C to obtain the nano-carbon fiber-based electrocatalyst prepared by the present invention;

Wherein, said electrochemical deposition includes chronogalvanic deposition, chronopotential deposition, cyclic voltammetry deposition and pulse current deposition.

Beneficial effect

The present invention utilizes the unique physical and chemical properties of the nano-carbon fiber carrier, including special microstructure, surface properties and unique mesopore size distribution, combines the advantages of the gel method and the electrochemical deposition method in the preparation of noble metal catalysts, and simultaneously abandons the gel method and electrodeposition method. The shortcomings of the chemical deposition method in the preparation process make the prepared noble metal catalysts have the characteristics of high dispersion, high load and high utilization rate.

The particle size and dispersion of the electrocatalyst obtained in the present invention can be characterized by a high-resolution transmission electron microscope (HRTEM) (see Figure 2), and the electrochemical performance can be measured by a polarization experiment of an oxygen electrode. The preparation method of the oxygen electrode: a certain amount of electrocatalyst, Nafion solution, PTFE emulsion and dispersant (a mixture of absolute ethanol and water, the volume ratio is 1:1) are mixed under supersonic vibration to prepare ink-like slurry, Then it was evenly transferred to water-repellent treated carbon paper for drying. Under the pressure of 6-9MPa, the oxygen electrode for testing is obtained. The electrochemical test is carried out in a three-electrode two-loop system, the oxygen electrode and the auxiliary electrode form a loop, and the reference electrode is a saturated calomel electrode.

Description of drawings

Fig. 1 is the polarization curve diagram of the noble metal electrocatalyst electrode based on carbon nanofiber prepared in implementation 1-7.

Figure 2 is a TEM image of carbon nanofiber supported Pd metal electrocatalysts.

Detailed ways

Example 1

5 grams of tubular carbon nanofibers were added to 50ml of 4M NaOH solution for washing for 2 hours, then filtered and washed until the pH value was equal to 7.0. Then put the filtered carbon nanofibers into a drying oven at 120° C. for drying. Tubular carbon nanofibers were treated with NaOH followed by HCl. First put the NaOH-treated tubular carbon nanofibers into 60ml of 2M HCl solution and wash at 60°C for 4 hours. It was then filtered and dried overnight in a 120°C drying oven. The washed tubular carbon nanofibers were oxidized in an air atmosphere at 250° C. for 6 hours, extracted with ethanol for 12 hours after treatment, and then vacuum-dried before use.

Get 1 gram of purified and activated tubular carbon nanofibers, add 9 grams of water, make the carbon nanofiber mass percentage obtained through ultrasonic dispersion be 10% A solution, get 2.5 grams of polytetrafluoroethylene containing 60% polytetrafluoroethylene Add 22.5 grams of water to the emulsion, and dilute it into a polytetrafluoroethylene solution B with a mass percentage of 6%. In a water bath at 80°C, put the mixed liquid A in a beaker, and gradually add the solution B under vigorous stirring. Continue to stir until a gel forms. Afterwards, the obtained jelly was evenly coated on the nickel foam, and pressed into a tablet at 250° C. under a pressure of 5 MPa to obtain a tubular carbon nanofiber electrode.

At room temperature, take 0.5 g of Pd(Cl) ₂ and add 10 ml of 1M HCl to dissolve it. Then, 10 ml of polyethylene glycol solution was added to the prepared H ₂ PdCl ₄ solution, and at the same time, 4M NaOH solution was added dropwise until the pH was greater than 12. Afterwards, the obtained solution was transferred to a three-necked flask, stirred vigorously in a constant temperature water bath at 33°C and kept for 3 h. Then, the temperature was raised to 110°C at a heating rate of 10°C/min and kept for 3h. After the above treatment, the solution was cooled to 80°C and stabilized for 30 minutes, then slowly added dropwise 1M HCl solution to adjust the pH to 3, and then stabilized for 10 minutes. After the solution stabilized, 10 ml of PVP was added.

The obtained carbon nanofiber electrode was placed in the metal Pd sol prepared above, and was stabilized for 30 min under the protection of Ar. Using the Pd electrode as the anode and the saturated calomel electrode as the cathode (SCE), electrodeposition was carried out at a temperature of 50°C and a voltage of -0.10V relative to the equilibrium potential. The deposition time was 10min, and the Pd loading was 10wt%. Electrocatalyst electrodes based on tubular carbon nanofibers. It can be seen from the TEM photographs that the electrocatalyst is uniformly distributed with an average particle size of 3 nm. The electrochemical characterization of the oxygen electrode is shown in Figure 1.

Example 2:

Take 1 gram of the purified and activated tubular carbon nanofibers in Example 1, and prepare the required tubular carbon nanofiber electrodes according to the method in Example 1. The metal sol was prepared according to the method for preparing the Pd metal sol in Example 1, and the difference from Example 1 was that the concentration of Pd(Cl) was _doubled .

Similar to Example 1, the obtained tubular carbon nanofiber electrode was placed in the Pd metal sol prepared above, and was stabilized for 30 min under the protection of Ar. The Pd electrode was used as the anode, the saturated calomel electrode was used as the cathode, the temperature was 40°C, the electrodeposition was carried out at -0.05V relative to the equilibrium potential, and the deposition time was 25min. catalyst electrodes. It can be seen from the TEM photographs that the electrocatalyst is uniformly distributed and the average particle size is 4nm. The electrochemical characterization of the oxygen electrode is shown in Figure 1.

Example 3:

Take 5 grams of plate-type carbon nanofibers, and perform pretreatment according to the purification and activation process of tube-type carbon nanofibers in Example 1. Take 1 gram of plate-type carbon nanofibers and add 5ml of 2wt% Nafion solution. After ultrasonic dispersion, the mixed solution was taken out with a pipette gun and dropped on the glassy carbon electrode, and then dried naturally under air atmosphere for 1 h. The required plate-type carbon nanofiber electrocatalyst is obtained.

According to the method described in Example 1, Pd metal sol was prepared. Similar to Example 1, the obtained plate-type carbon nanofiber electrode was placed in Pd metal sol and stabilized for 30 min under the protection of Ar atmosphere. Using the Pd electrode as the anode and the saturated calomel electrode as the cathode, electrodeposition was carried out at -0.10V relative to the equilibrium potential, and the deposition time was 9min to obtain a tubular carbon nanofiber-based electrocatalyst electrode with a Pd loading of 10wt%. It can be seen from the TEM photographs that the electrocatalyst is uniformly distributed with an average particle size of 3 nm. The electrochemical characterization of the oxygen electrode is shown in Figure 1.

Example 4:

Take 5 grams of herringbone carbon nanofibers, and perform pretreatment according to the purification and activation process of tubular carbon nanofibers in Example 1. Take 1 gram of treated herringbone carbon nanofibers and take 0.5 gram of polyethylene glycol in a ratio of 2:1. Fully mix the carbon nanofibers and polyethylene glycol, and press into tablets at room temperature and under a pressure of 5 MPa to obtain a fishbone carbon fiber electrocatalyst.

The Pt metal sol was prepared according to the method described in Example 1. Similar to Example 1, the process of preparing the sol is just changing Pd(Cl) ₂ to Pt(Cl) ₂ .

According to the method described in Example 1, the fishbone carbon nanofiber electrode was placed in the Pt metal sol. The bulk Pt electrode was used as the counter electrode, and the electrochemical deposition was carried out at a relative equilibrium potential of 0.10V. The deposition time was 9 minutes, and a fishbone-based carbon nanofiber electrocatalytic electrode with a Pt loading of 30 wt% was obtained. It can be seen from the TEM photographs that the electrocatalyst is uniformly distributed with an average particle size of 5 nm. The electrochemical characterization of the oxygen electrode is shown in Figure 1.

Example 5:

Take 1 gram of herringbone carbon nanofibers purified and activated according to Example 4, and take 0.5 gram of phenolic resin in a ratio of 2:1. Fully mix the herringbone carbon nanofibers and phenolic resin, and press them into tablets at room temperature and under a pressure of 5 MPa to obtain a molded body of herringbone carbon nanofibers and phenolic resin. The obtained molded body was put into a muffle furnace, cured at 120°C for 12 hours under the protection of Ar atmosphere, and then carbonized and formed at 800°C for 8 hours under the protection of Ar atmosphere to obtain the desired fishbone carbon nanofiber electrode.

According to the method described in Example 1 and Example 4, Pt metal sol and Pd metal sol were prepared respectively.

According to Example 1, the prepared herringbone carbon nanofibers were placed in Pt metal sol. According to the description in Example 4, with a Pt electrode as a counter electrode and a saturated calomel electrode as a reference electrode, metals were electrochemically deposited by cyclic voltammetry scanning at room temperature. The scanning interval is at the equilibrium potential ±0.50V, and the scanning time is 20 minutes, and a fishbone carbon nanofiber-based electrocatalyst with a Pt loading of 5wt% is obtained.

On the basis of the above work, the prepared fishbone-based carbon nanofiber electrocatalyst electrode was placed in the prepared Pd colloid solution and stabilized for 30 min. Then, the Pd electrode was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode, and the metal was deposited by galvanostatic scanning at room temperature. The electric current is 0.15mA, and the deposition time is 5min, so that the electrocatalyst based on fishbone carbon nanofibers with Pt and Pd contents of 5wt% respectively is prepared. From the TEM photos, it can be seen that the electrocatalyst is uniformly distributed and the average particle size is 3.5nm. The electrochemical characterization of the oxygen electrode is shown in Figure 1.

Embodiment 6:

Take 1 gram of plate-type carbon nanofibers purified and activated according to Example 3, and prepare plate-type carbon nanofiber electrodes according to the method described in Example 1. Compared with Example 1, other conditions are the same except that plate-type carbon nanofibers are used.

According to the method described in Example 1 and Example 4, Pt metal sol and Ru metal sol were prepared respectively.

According to Example 1, the prepared plate-type carbon nanofibers were placed in Pt metal sol. According to the description in Example 4, with a Pt electrode as a counter electrode and a saturated calomel electrode as a reference electrode, metals were electrochemically deposited by cyclic voltammetry scanning at room temperature. The scanning interval is at the equilibrium potential ±0.50V, and the scanning time is 20 minutes, and a fishbone carbon nanofiber-based electrocatalyst with a Pt loading of 5wt% is obtained.

On the basis of the above work, the prepared plate-based carbon nanofiber electrocatalyst electrode was placed in the prepared Ru colloidal solution and stabilized for 30 min. Then, the Ru electrode was used as the counter electrode and the saturated calomel electrode was used as the reference electrode, and the metal was deposited by galvanostatic scanning at room temperature. The electric current is 0.05 mA, and the deposition time is 15 min, so that the plate-type carbon nanofiber-based electrocatalyst with Pt and Ru contents of 5 wt % respectively is prepared. It can be seen from the TEM photographs that the electrocatalyst is uniformly distributed and the average particle size is 4nm. The electrochemical characterization of the oxygen electrode is shown in Figure 1.

Embodiment 7:

Take 1 gram of plate-type carbon nanofibers purified and activated according to Example 3, and prepare plate-type carbon nanofiber electrodes according to the method described in Example 1. Compared with Example 1, other conditions are the same except that plate-type carbon nanofibers are used.

According to the method described in Example 1 and Example 4, Pt metal sol and Pd metal sol were prepared respectively.

According to Example 1, the prepared plate-type carbon nanofibers were placed in Pt metal sol. According to the description in Example 4, with a Pt electrode as a counter electrode and a saturated calomel electrode as a reference electrode, metals were electrochemically deposited by cyclic voltammetry scanning at room temperature. The scanning interval is at the equilibrium potential ±0.60V, and the scanning time is 25 minutes, and a fishbone carbon nanofiber-based electrocatalyst with a Pt loading of 10wt% is obtained.

On the basis of the above work, the prepared fishbone-based carbon nanofiber electrocatalyst electrode was placed in the Pd colloidal solution and stabilized for 30 min. Then, the Pd electrode was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode, and the metal was deposited by pulsed current scanning at room temperature. The current is 0.15±0.05mA, and the deposition time is 6min, so that a plate-type carbon nanofiber-based electrocatalyst with a Pt loading of 10wt% and a pd loading of 7wt% is prepared. It can be seen from the TEM photographs that the electrocatalyst is uniformly distributed and the average particle size is 4nm. The electrochemical characterization of the oxygen electrode is shown in Figure 1.

Claims (6)

1, a kind of preparation method of the noble metal electrocatalyst based on carbon nano-fiber, it is characterized in that, noble metal is dispersed on the nano-carbon fibre carrier, wherein, described carbon nano-fiber is that diameter is carbon nanofibers, the plshy bone open Nano carbon fibers peacekeeping tubular type carbon nano-fiber of 1-200nm, and said noble metal comprises Pt, Pd, in the Ru metal one or more, bullion content is 5-30wt% in the eelctro-catalyst, the noble metal particle diameter is between 2-6nm;

Described method comprises following concrete steps:

(1) purifying of carbon nano-fiber and activation:

A) with carbon nano-fiber under 80 ℃, with the NaOH of 4M washing 2 hours, filter, washing again, equal 7.0 up to the pH value, in 120 ℃ drying box, carry out drying then; Step a) repeats 4 times;

B) carbon nano-fiber that repeating step a) is obtained after 4 times places 2M HCl solution washing 4 hours under 60 ℃, refilters, washs, and equals 7.0 up to the pH value, carries out drying then in 120 ℃ drying box; Step b) repeats 3 times;

C) with repeating step b) carbon nano-fiber that obtains after 3 times carries out oxidation processes in 250 ℃ of air atmosphere, and the processing time is 6h, handles the back with absolute ethyl alcohol extracting 12h, and is stand-by after the vacuum drying afterwards;

(2) carbon nano-fiber electrode preparation

Nano carbon fibers peacekeeping binding material normal temperature through purifying and activation is mixed down, preparation carbon nano-fiber electrode, binding material content accounts for the 1-99% of Nano carbon fibers peacekeeping binding material gross mass,

Wherein: said binding material is that the polyethylene glycol, epoxy resin and the mass percent that are selected from polytetrafluoroethylsolution solution that mass percent is 1-80%, purity 100% is a kind of in the Nafion solution of 2-30%;

(3) noble metal catalyst colloidal sol preparation

Getting described noble metal precursor body, is 1%～30% HCl, NH by the adding mass percent ₃, NaOH or absolute ethyl alcohol, form mass percent and be 0.1%～25% precious metal solution, afterwards, adding an amount of mass percent in solution is the stabiliser solution of 0.1%-10%, adds NaOH solution simultaneously, until the pH of gained solution greater than 12; The above-mentioned solution that obtains is stirred, and in 33 ℃ oil bath, kept 3 hours; Afterwards, under the programming rate of 10 ℃/10min, be warming up to 110 ℃, and kept 3 hours; Then, be cooled to 80 ℃ and also stablize 30min, slowly dripping 1MHCl regulator solution pH again is 3, stablizes 10min; At last, add reducing agent, and kept 2 hours, both obtained needed noble metal colloidal sol at 80 ℃;

Wherein, said stabilizing agent comprises: a kind of in the solution of polyethylene glycol, positive silicic acid fat, polyvinyl pyridine, polyvinyl alcohol, natrium citricum, trioctylphosphine hydrogen phosphide,

Said reducing agent comprises: mass percent is a kind of in 10%～100% hydrogen, ethanol, acetaldehyde, diamine, carbon monoxide, polyethylene glycol, the PVP;

(4) based on the preparation of the noble metal electrocatalyst of carbon nano-fiber

At room temperature, the carbon nano-fiber electrode of step (2) preparation is placed the prepared noble metal catalyst colloidal sol of step (3), be to electrode with corresponding noble metal electrode simultaneously, in with respect to equilibrium potential ± 0.50V scope, carry out electrochemical deposition, depositing temperature is 0-80 ℃, sedimentation time is 5-60min, be the carbon nano-fiber noble metal electrocatalyst electrode that obtains 7.0 with the ultra-pure water washing up to the pH value then, dry in 40-50 ℃ Ar atmosphere again, promptly obtain prepared noble metal electrocatalyst based on carbon nano-fiber;

Wherein, said electrochemical deposition comprises timing electric current deposition, time-measuring electric potential deposition, cyclic voltammetric deposition and pulse current deposition.

2, the preparation method of the noble metal electrocatalyst based on carbon nano-fiber as claimed in claim 1 is characterized in that in step (2), binding material content accounts for the 5-50wt% of Nano carbon fibers peacekeeping binding material gross mass.

3, the preparation method of the noble metal electrocatalyst based on carbon nano-fiber as claimed in claim 2 is characterized in that in step (2), binding material content accounts for the 10-30wt% of Nano carbon fibers peacekeeping binding material gross mass.

4, the preparation method of the noble metal electrocatalyst based on carbon nano-fiber as claimed in claim 1 is characterized in that, depositing temperature is 10-60 ℃ in the step (4).

5, the preparation method of the noble metal electrocatalyst based on carbon nano-fiber as claimed in claim 1 is characterized in that, sedimentation time is 5-30min in the step (4).

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