CN110975913A

CN110975913A - Electrocatalyst for electrocatalytic hydrogen production and preparation method thereof

Info

Publication number: CN110975913A
Application number: CN201911006595.0A
Authority: CN
Inventors: 姚伟峰; 石英
Original assignee: Shanghai Electric Power University
Current assignee: Shanghai University of Electric Power; Shanghai Electric Power University; University of Shanghai for Science and Technology
Priority date: 2019-10-22
Filing date: 2019-10-22
Publication date: 2020-04-10

Abstract

The invention discloses an electrocatalyst for hydrogen production by electrocatalytic decomposition of water, which is characterized by having a chemical formula of Co_x-N-C, wherein 0<x ≦ 2. The invention also provides a preparation method of the electrocatalyst, which comprises the following steps: transferring office waste paper into a high-pressure reaction kettle, adding water for hydrothermal reaction at the temperature of 200 ℃, centrifuging and filtering a product to obtain carbon quantum dots; with Co (NO)₃)₂·6H₂Mixing O and urea, calcining for 1h in argon atmosphere at 800 ℃, cleaning and drying to obtain the electrocatalyst Co_x-N-C. The invention adopts hydrothermal and high temperature pyrolysis methods to control and synthesize the electrocatalyst with different Co contents, the method is simple and feasible, the efficiency is high, the large-scale production can be realized, and the electrocatalytic activity of the electrocatalyst is greatly improved.

Description

Electrocatalyst for electrocatalytic hydrogen production and preparation method thereof

Technical Field

The invention belongs to the field of chemical industry, and particularly relates to an electrocatalyst for hydrogen production by electrocatalytic decomposition of water and a preparation method thereof.

Background

Energy shortage is a major challenge facing human beings at present, and is a major problem that the sustainable development strategy implemented in our country must be prioritized. As one of the main forms of new energy, research and development and application of hydrogen energy have attracted much attention. The water electrolysis hydrogen production is a low-cost and high-purity hydrogen production method, and is an important way for solving the global environmental pollution and energy crisis at present.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides an electrocatalyst for electrocatalytic decomposition of water to produce hydrogen and a preparation method thereof, and the electrocatalyst and the preparation method thereof aim to solve the problems of poor source and high preparation economic cost of the existing electrocatalyst.

In order to solve the technical problem, the invention provides an electrocatalyst for hydrogen production by electrocatalytic decomposition of water, which is characterized in that the chemical formula of the electrocatalyst is Co_x-N-C, wherein 0<x≦2。

Preferably, the electrocatalyst has the formula Co_0.2-N-C。

Preferably, the electrocatalyst has the formula Co_0.6-N-C。

Preferably, the electrocatalyst has the formula Co_1.2-N-C。

Preferably, the electrocatalyst has the formula Co_1.8-N-C。

The invention also provides a preparation method of the electrocatalyst for preparing hydrogen by electrocatalytic decomposition of water, which is characterized by comprising the following steps:

step 1: transferring the material rich in cellulose into a high-pressure reaction kettle, adding deionized water, carrying out hydrothermal reaction for 8-24 h at 180-250 ℃, centrifuging and filtering a product, and carrying out freeze drying at-50 ℃ for 24-48 h to obtain carbon quantum dot powder;

step 2: adding the carbon quantum dot powder prepared in the step 1 into Co (NO)₃)₂·6H₂Stirring and reacting in O water solution for 12h, and freeze-drying at-50 ℃ for 24-48 h to obtain Co_x-a powder of C;

and step 3: the Co prepared in the step 2 is added_xMixing and grinding the-C powder and urea, calcining for 1-2 hours at 800-1000 ℃ in an inert gas atmosphere, soaking the calcined material in an acid solution, cleaning, centrifuging and drying to obtain the electrocatalyst Co for hydrogen production by electrocatalytic decomposition of water_x-N-C。

Preferably, the material rich in cellulose in step 1 is waste material rich in cellulose, such as office waste paper or leaves.

Preferably, the centrifugal rotation speed in the step 1 is 8000-13000 rpm.

Preferably, the filtration in step 1 is to collect the supernatant by using 0.22 μm membrane filtration.

Preferably, in the step 2, the carbon quantum dot powder is mixed with Co (NO)₃)₂·6H₂The mass ratio of O is 100 (1-18).

Preferably, in the step 3, Co_xThe mass ratio of the-C powder to the urea is 1: 10.

Preferably, in the step 3, soaking in an acid solution is to put the calcined material at 0.5M H₂SO₄Soaking in the solution for 24h to remove calcium impurities in the waste paper.

Preferably, in the step 3, the cleaning includes: firstly use 0.5M H₂SO₄The solution is washed for several times, then washed with deionized water for several times until neutral, and finally washed with ethanol for several times.

Preferably, in the step 3, the centrifugal speed is 8000 rpm.

Preferably, in the step 3, the drying is carried out for 8 hours at 60 ℃ under vacuum.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention selects Co_xthe-N-C electrocatalyst is a research object, the research on electrocatalytic hydrogen production is developed, and the composition of the electrocatalyst is changed to successfully develop novel Co with higher electrocatalytic hydrogen production activity_1.2-N-C electrocatalyst.

(2) The invention adopts a hydrothermal method to control waste paper to synthesize carbon quantum dots as a main carbon source, urea as a nitrogen source and Co (NO)₃)₂·6H₂O is used as a cobalt source, and the electrocatalyst is synthesized by a high-temperature pyrolysis method, so that the method is simple and feasible, high in yield, low in production cost and beneficial to large-scale popularization.

(3) The invention applies the carbon quantum dots to the aspect of electrocatalysis hydrogen production, and widens the way for the application of the carbon quantum dots.

Drawings

FIG. 1 shows an electrocatalyst Co according to the invention_x-a schematic of the synthesis of N-C;

FIG. 2 shows an electrocatalyst, Co, prepared in example 3 of the present invention_1.2-XRD pattern of N-C;

FIG. 3 shows an electrocatalyst, Co, prepared in example 3 of the present invention_1.2-N-C Transmission Electron Microscopy (TEM) images; 3a, 3b, 3c is an electrocatalyst Co_1.2TEM images of N-C at different magnifications (scale: 0.5 μm,100nm,10 nm); 3d is the EDS spectrum of C, N, O, Co (scale: 250 nm);

FIG. 4 shows an electrocatalyst, Co, prepared in example 3 of the present invention_1.2-high power transmission electron microscopy (HRTEM) of N-C;

FIG. 5 shows the electrocatalyst Co prepared in example 3 of the present invention_1.2-XPS spectra of N-C; 5a is Co_1.2-total spectrum of N-C, 5b Co2p, 5C 1s, 5d N1 s;

FIG. 6a is CQDs, N-C, Co_x-N-C in N₂Saturation 0.5M H₂SO₄Polarization curves in the electrolyte (x ═ 0.2,0.6,1.2, 1.8);

FIG. 6b is 10mA cm^-2Of Ti-Co_x-N-C electrocatalyst Co content versus overpotential;

FIG. 7 is Co_x-Tafel curve of N-C (x ═ 0,0.2,0.6,1.2, 1.8);

FIG. 8a shows the frequency value set between 1Hz and 100kHz and the voltage of 500mV at 0.5M H₂SO₄Co measured in solution_x-Nyquist plot for N-C (x ═ 0,0.2,0.6,1.2, 1.8);

FIG. 8b is an equivalent circuit model of an electrochemical impedance test;

FIG. 8c is a graph of electrochemical stability test for 14h of continuous measurement;

FIG. 8d Co cycles 2000 and 3000_1.2-N-C polarization curve;

FIG. 9 is Co_xCyclic voltammograms of N-C (x ═ 0,0.2,0.6,1.2, 1.8).

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

As shown in fig. 1, this example provides a method for preparing the above electrocatalyst for hydrogen production by electrocatalytic decomposition of water, which includes the following specific steps:

step 1: crushing 2g of office waste paper, dispersing the office waste paper in 60mL of water, transferring the office waste paper into a 100mL Teflon-lined stainless steel autoclave, carrying out hydrothermal reaction for 8h at 200 ℃, naturally cooling to room temperature to obtain a dark brown solution containing precipitate particles, centrifuging at 8500rpm for 0.5h to remove large precipitates, collecting the precipitate particles, filtering the supernatant with a 0.22 mu m filter paper membrane, and freeze-drying the supernatant for 48h to obtain brown Carbon Quantum Dots (CQDs) powder;

step 2: 200mg of the carbon quantum dot powder prepared in step 1 was added to 20mL of Co (NO) having a concentration of 0.1mg/mL₃)₂·6H₂Stirring in O water solution at 400rpm for 12 hr, freeze drying, and collecting to obtain Co_x-a powder of C;

and step 3: the Co prepared in the step 2 is added_xMixing and grinding-C powder and urea (mass ratio is 1:10) for 0.5h, then placing in a tube furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under argon atmosphere, keeping the temperature for 1h, placing the obtained powder in a container with 0.5MH₂SO₄Soaking in the solution for 24 hr, and soaking in 0.5M H₂SO₄Sequentially cleaning water and ethanol for multiple times, and drying in a vacuum oven at 60 ℃ for 12h to obtain the electrocatalyst Co for preparing hydrogen by electrocatalytic decomposition of water_0.2-N-C。

Example 2

Example 2 differs from example 1 in that Co (NO) is present in step 2₃)₂·6H₂The concentration of the O aqueous solution is 0.3mg/mL, the rest steps are the same as the step 1, and finally the electrocatalyst Co for preparing hydrogen by electrocatalytic decomposition of water is obtained_0.6-N-C。

Example 3

Example 3 differs from example 1 in that Co (NO) is present in step 2₃)₂·6H₂The concentration of the O aqueous solution is 0.6mg/mL, the rest steps are the same as the step 1, and finally the electrocatalyst Co for preparing hydrogen by electrocatalytic decomposition of water is obtained_1.2-N-C。

FIG. 2 shows an electrocatalyst Co_1.2-XRD pattern of N-C. As shown in fig. 2, the broad peak at 26 ° is associated with the (002) plane of amorphous carbon. The peak at 43.5 ° is small and can be attributed to the crystal plane (101) of carbon. Due to Co_1.2Co doping in the-N-C samples is limited (only 1.2 wt% by weight), Co being present in the XRD spectrum_1.2the-N-C has no characteristic peak of metallic Co crystal.

FIG. 3 shows an electrocatalyst, Co_1.2Transmission Electron Microscopy (TEM) image of N-C. The TEM images of FIGS. 3a, 3b, 3c are Co_1.2TEM images of the N-C catalyst at different magnifications (scale: 0.5 μm,100nm,10 nm); FIG. 3d is an EDS spectrum (scale: 250nm) TEM image of C, N, O, Co showing that Co_1.2-N-C is a stacked nanosheet structure having a size greater than 3 μm. The results show that under the current experimental conditions, carbon sheets of larger size can be formed. Furthermore, Co_1.2TEM images of-N-C (FIGS. 3b, 3C) also show a uniform distribution of nano-sized nanoparticles on the flakes.

FIG. 4 shows an electrocatalyst Co_1.2High power transmission electron microscopy (HRTEM) of-N-C, Co_1.2Lattice fringes of-N-C nanoparticles of

This is very close to the lattice fringes of the (111) crystal plane of Co metal, indicating that Co is produced_1.2Cobalt metal nanoparticles are uniformly dispersed in the-N-C.

FIG. 5 is Co_1.2XPS spectra of (a) Co of (N-C)_1.2-a global spectrum of N-C (b) Co2 p; (c) c1 s; (b) co2 p; (d) n1 s. From Co_1.2General spectra of-N-C We can see Co_1.2The main constituent element of-N-C is C, N, O, Co, with the highest content of C. High resolution Co2p XPS spectra explained Co_1.2Presence of surface Co atoms in N-C samples. The 2p3/2 transition of Co can be characterized by three peaks; 7Co-Co at 78.3eV, Co-O at 779.2 eV and Co-N at 781.6 eV. A typical satellite peak 786.1eV wide indicates Co²⁺Is Co_1.2The predominant valence state of the N-C surface. The C1s spectrum has three distinct peaks at 284.8eV, 286.3eV and 289.9eV, which may correspond to those of C-C/C-C, N-C/C-O and C-Co, respectively. The N1s spectrum can be formed by two peaks corresponding to pyridine nitrogen and pyrrole nitrogen when the binding energy is 398.2eV and 400.2eV respectively, and can be used as the coordination site of a Co atom. Particularly, carbon atoms near pyridine N are used as active sites, so that the corresponding hydrogen evolution catalytic performance is improved.

Example 4

Example 4 differs from example 1 in that Co (NO) is present in step 2₃)₂·6H₂The concentration of the O aqueous solution is 0.9mg/mL, the rest steps are the same as the step 1, and finally the electrocatalyst Co for preparing hydrogen by electrocatalytic decomposition of water is obtained_1.8-N-C。

Comparative example 1

The embodiment provides a preparation method of a Co-free electrocatalyst, which comprises the following specific steps:

step 2: mixing and grinding 200mg of the carbon quantum dot powder prepared in the step 1 and urea (the mass ratio is 1:10) for 0.5h, then placing the mixture in a tube furnace, heating to 800 ℃ at the heating rate of 5 ℃/min under the argon atmosphere, preserving the heat for 1h, placing the obtained powder in 0.5M H₂SO₄Soaking in the solution for 24 hr, and soaking in 0.5M H₂SO₄And sequentially washing the catalyst, water and ethanol for many times, and drying the catalyst in a vacuum oven at the temperature of 60 ℃ for 12 hours to obtain the Co-free electrocatalyst N-C.

Electrocatalytic hydrogen evolution performance test

The electrochemical test assay is in CHI660E was done on an electrochemical workstation using a three electrode test system. The preparation method of the working electrode comprises the following steps: co prepared by the above method_xThe powder of (e) -N-C (x ═ 0,0.2,0.6,1.2,1.8) was dissolved in 490 μ L of deionized water, 490 μ L of ethanol and 10 μ L of 5% Nafion solution in a weighed amount, and dispersed uniformly by sonication for 30 minutes. Dropping 7 μ L of sample solution on a glassy carbon electrode (GCE, 3mm diameter), and naturally drying; the auxiliary electrode is a carbon rod; the reference electrode was a Saturated Calomel Electrode (SCE).

Concentration of electrolyte N₂Saturated 0.5M H₂SO₄The scanning speed of the solution is 50 mV.s^-1The electrochemical activity (polarization curve test) is tested under the condition of (1), and the voltage test range is 0V to-0.8V. As shown in FIG. 6a, as the Co content increases, the Co content increases_xIncreased activity of the-N-C catalyst. HER activity increased from x-0 and Co when x-1.2_1.2the-N-C activity reaches a maximum and a further increase in x to 1.8 results in a slight decrease in activity. The reason for the change in activity is Co_xCo in-N-C may form a Co-N bond, and when all Co and N atoms form a Co-N bond, Co_1.2Excess Co in the-N-C will mask the Co-N bond, resulting in Co_xThe activity of the-N-C catalyst decreases. Co_xCatalyst of (1) N-C (x ═ 0,0.2,0.6,1.2,1.8) at a current density of 1mA cm^-2Is 488, 175, 158, 135 and 130mV, respectively. Co_xThe properties of-N-C are more active than the unmodified carbon quantum dot samples. As shown in FIG. 6b, Co_0.2-N-C、Co_0.6-N-C、Co_1.2-N-C and Co_1.8-N-C at 10mA cm^-2The overpotentials at (a) are 287, 274, 226 and 227mV, respectively. These results again show that Co_xThere is an optimum value for x for the N-C catalyst. Co of 1.2 x in the catalysts studied_xThe highest N-C activity.

FIG. 7 is Co_xTafel curve Co of-N-C (x ═ 0,0.2,0.6,1.2,1.8)_x-N-C, x ═ 0.2,0.6,1.2,1.8 catalysts having Tafel slopes of 106, 111, 91 and 114mV · dec, respectively^-1The Tafel slopes are all less than CQDs (436mV dec)^-1) And N-C sample (230mV dec)^-1). Demonstrating the different cobalt contents on the catalystThe catalytic activity has a great influence.

Electrochemical impedance testing

The frequency value is set between 1Hz and 100kHz, the voltage is 500mV, and the equivalent circuit model is shown in FIG. 8b at N₂Saturated 0.5M H₂SO₄Co measured in solution_xNyquist plot for-N-C, as shown in FIG. 8a, Co_1.2Nyquist curve ratio Co of-N-C catalyst_xThe Nyquist curve for the-N-C catalyst is much smaller, indicating Co_1.2Charge transfer resistance (R) between the N-C catalyst particles and the electrolyte_ct) The minimum and the optimum content of Co can increase Co_xHydrogen production rate of N-C catalyst.

Electrocatalytic hydrogen evolution stability test

In N₂Saturated 0.5M H₂SO₄In solution at 50mV · s^-1Is cycled 2000 and 3000 times at a scan rate of 2mV · s^-1Is measured, fig. 8c is an electrochemical stability test curve for 14 hours of continuous measurement, and fig. 8d is Co at 2000 and 3000 cycles_1.2-N-C polarization curve. The drop is small relative to the initial LSV curve at the same current density. The time ampere curve shows that Co is present after 14 hours of continuous scanning_1.2The better stability of the-N-C can be still maintained. This result indicates that the Co1.2-N-C catalyst is stable in corrosive acidic electrolytes.

Electrocatalytic active surface area test

The Electrochemically Active Surface Area (EASA) of the material was calculated by hydrogen adsorption, and FIGS. 9a to 9e are Co_xCyclic voltammograms of-N-C (x ═ 0,0.2,0.6,1.2,1.8) at scan rates of 20-200 mv s^-1At 0.5MH₂SO₄In the solution, the potential range is 0.15-0.05V vs RHE. FIG. 9f is Co_x-N-C current density versus potential scan rate. The double-layer capacitance (C) can be obtained from the curve of the current (j) along with the scanning speed_dl) It is evident that at 0.5MH₂SO₄Medium, N-C, Co_0.2-N-C、Co_0.6-N-C、 Co_1.8-N-C、Co_1.2The capacitances of-N-C are 2, respectively.74. 3.73, 6.6, 12.65 and 14.6 mF-cm^-2。 Co_xThe sequences of the-N-C catalyst ECSAs are in accordance with the sequence of electrocatalytic activity properties described above. This result indicates that Co_xThe electrochemical activity of-N-C is directly related to the effect of ECSA. When x is 1.2, Co_1.2the-N-C catalyst showed the highest ECSA value, showing the most active sites.

Claims

1. An electrocatalyst for hydrogen production by electrocatalytic decomposition of water, characterized in that it has the chemical formula of Co_x-N-C, wherein 0<x≦2。

2. The electrocatalyst for electrocatalytic decomposition of water to produce hydrogen according to claim 1, wherein the electrocatalyst is Co_xAnd x in the-N-C is one of 0.2,0.6,1.2 or 1.8.

3. The method for preparing an electrocatalyst for electrocatalytic decomposition of water to produce hydrogen according to claim 1 or 2, comprising the steps of:

step 1: material rich in cellulose) is transferred into a high-pressure reaction kettle, deionized water is added to carry out hydrothermal reaction for 8-24 hours at the temperature of 180-250 ℃, and the product is centrifuged, filtered and freeze-dried for 24-48 hours at the temperature of-50 ℃ to obtain carbon quantum dot powder;

4. The method for preparing the electrocatalyst for hydrogen production by electrocatalytic decomposition of water according to claim 3, wherein the cellulose-rich material in step 1 is office waste paper or leaves.

5. The preparation method of the electrocatalyst for hydrogen production by electrocatalytic decomposition of water according to claim 3, wherein the centrifugal rotation speed in the step 1 is 8000-13000 rpm.

6. The method for preparing an electrocatalyst for electrocatalytic decomposition of water to produce hydrogen according to claim 3, wherein the filtering in step 1 is to collect the supernatant by 0.22 μm membrane filtration.

7. The method of preparing an electrocatalyst for electrocatalytic decomposition of water to produce hydrogen as claimed in claim 3, wherein in step 2, the carbon quantum dot powder is mixed with Co (NO)₃)₂·6H₂The mass ratio of O is 100 (1-18).

8. The method for preparing the electrocatalyst for electrocatalytic decomposition of water to produce hydrogen according to claim 3, wherein in the step 3, Co is used_xThe mass ratio of the-C powder to the urea is 1: 10.

9. The method for preparing the electrocatalyst for hydrogen production by electrocatalytic decomposition of water according to claim 3, wherein in the step 3, the material after calcination is soaked in an acid solution, specifically, the material after calcination is placed in a solution of 0.5M H₂SO₄Soaking in the solution for 24 h.

10. The method for preparing an electrocatalyst for electrocatalytic decomposition of water to produce hydrogen according to claim 3, wherein the washing in step 3 comprises: firstly use 0.5M H₂SO₄Cleaning with the solution for several times, cleaning with deionized water for several times until the solution is neutral, and finally cleaning with ethanol for several times; the centrifugation speed is 8000 rpm; drying is carried out for 8h under vacuum at 60 ℃.