A basic her catalyst electrode and a method for preparing the same

Abstract

The application belongs to the field of catalysis technology, and particularly relates to a basic HER catalyst electrode and a preparation method thereof. The preparation method of the basic HER catalyst electrode provided by the application comprises the following steps: 1) mixing CoCl2, NiCl2, urea and water to obtain a mixed solution; 2) immersing foamed nickel in the mixed solution in step 1) to perform a hydrothermal reaction, cooling, washing and drying to obtain a precursor; and 3) calcining the precursor with sodium hypophosphite in a protective atmosphere, cooling, washing and drying to obtain the HER catalyst electrode. The catalyst electrode prepared by using CoCl2 and NiCl2 as raw materials has rich interface regions and fine and uniform microstructures, which is helpful to expose a large number of active sites and thus improve the basic HER catalytic activity.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of catalysis technology, and particularly relates to a basic HER catalyst electrode and a preparation method thereof. BACKGROUND

[0002] The water decomposition reaction is composed of two half-reactions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), however, the high activation energy leads to slow kinetics of HER and OER, thus requiring excessive energy consumption to achieve the required reaction rate. The noble metal catalysts (Pt, Ir and Ru) have been widely considered as the best catalysts for HER and OER, but their industrial application is severely limited by high cost, low storage capacity and low stability. Currently, the alkaline water electrolysis for hydrogen production is commonly used in industry, and the nickel mesh is generally used as the catalyst electrode. The anode OER reaction has little difference in activity with the noble metal IrO2, and the key is the cathode HER reaction, which has a large difference in activity between Ni and Pt. Therefore, it is of great significance to develop a cheap and efficient HER catalyst electrode for the cost reduction and promotion of water electrolysis for hydrogen production. The transition metal phosphates (TMPs) have attracted extensive attention due to their non-toxicity, good chemical stability, low cost and excellent catalytic activity in alkaline electrolyte. CoP3 becomes an outstanding representative among TMPs due to its high conductivity and stability, but the strong binding energy between CoP3 and hydrogen is not conducive to the subsequent hydrogen desorption process, thus leading to low alkaline HER catalytic activity of the catalyst electrode and limited catalytic effect. SUMMARY

[0003] Therefore, the technical problem to be solved by the present application is to overcome the defects of low HER catalytic activity and limited catalytic effect of the catalyst electrode in the prior art, so as to provide a basic HER catalyst electrode and a preparation method thereof.

[0004] The present application provides a preparation method of a basic HER catalyst electrode, comprising the following steps:

[0005] 1) mixing CoCl2, NiCl2, urea and water to obtain a mixed solution;

[0006] 2) immersing the foamed nickel into the mixed solution in step 1) to perform a hydrothermal reaction, cooling, washing and drying to obtain a precursor;

[0007] 3) calcining the precursor with sodium hypophosphite in a protective atmosphere, cooling, washing and drying to obtain the HER catalyst electrode.

[0008] Optionally, the components in step 1) can be mixed uniformly, for example, the uniform mixed solution can be obtained by magnetic stirring for 20 min, and the mixed solution is a transparent pink solution.

[0009] Preferably, the calcination temperature in step 3) is 350-450℃, and the calcination time is 2-3h.

[0010] Preferably, the heating rate of the calcination is 3-5℃ / min.

[0011] Preferably, the molar ratio of CoCl2, NiCl2 to urea in step 1) is (1-2.5):(1-1.5):6.

[0012] The usage ratio of NiCl2 to water is 1.5:(40-60) mol / L.

[0013] Preferably, the reaction temperature of the hydrothermal reaction in step 2) is 120-150℃, and the reaction time is 6-8h.

[0014] Optionally, the hydrothermal synthesis reaction is carried out in a polytetrafluoroethylene reaction kettle liner.

[0015] Optionally, the top surface of the nickel foam (NF) is covered with a polytetrafluoroethylene tape, so that the product is deposited on the other side of the nickel foam.

[0016] Preferably, the mass ratio of the precursor to sodium hypophosphite in step 3) is 1:(5-10);

[0017] And / or, the protective atmosphere is Ar.

[0018] The present application does not have special requirements for the equipment of calcination annealing, and typically non-limiting, calcination annealing uses a tube furnace, and after calcination, it is naturally cooled to room temperature.

[0019] Optionally, the precursor is loaded into one ceramic boat, and sodium hypophosphite is loaded into another ceramic boat, which are placed at two positions downstream and upstream of the gas inlet of the tube furnace for calcination.

[0020] Preferably, in step 2), the nickel foam is pretreated by cleaning;

[0021] And / or, the nickel foam is sequentially cleaned with acetone, ethanol, deionized water, hydrochloric acid solution and deionized water;

[0022] And / or, the concentration of the hydrochloric acid solution is 2-3M HCl;

[0023] And / or, the cleaning is ultrasonic cleaning, and the cleaning time is 10-15min.

[0024] Preferably, the drying temperature in each step is 60-80℃, and the drying time is 12-24h.

[0025] Preferably, the washing in each step is sequentially using water and ethanol;

[0026] and / or, the number of washing times is 3-5 times.

[0027] The washing mode can be selected from, but is not limited to, flushing, and the drying mode can be selected from, but is not limited to, vacuum drying.

[0028] The application also provides the alkaline HER catalyst electrode prepared by the preparation method.

[0029] The technical scheme of the application has the following advantages:

[0030] (1) The preparation method of the alkaline HER catalyst electrode provided by the application comprises the following steps: 1) mixing CoCl2, NiCl2, urea and water to obtain a mixed solution; 2) immersing foamed nickel in the mixed solution in step 1) to perform a hydrothermal reaction, cooling, washing, and drying to obtain a precursor; and 3) performing calcination on the precursor and sodium hypophosphite in a protective atmosphere, cooling, washing, and drying to obtain the HER catalyst electrode. In the preparation of the catalyst electrode by using CoCl2 and NiCl2 as raw materials, the morphology of the hydroxide precursor is more uniform, and the micro-particles are more dispersed, which can lead to a higher utilization rate of active sites. The NO 3- Hydroxide formed in the hydrothermal reaction is more likely to agglomerate, and the particles are easy to gather, which leads to a low utilization rate of active sites and poor performance. At the same time, the ΔG *H of the generated Ni2P is positive, which means that the hydrogen desorption ability is strong, so the Ni2P is combined with CoP3, and the ΔG *H of the overall catalytic material is adjusted to the middle position. The catalytic electrode has a rich interface area and a small and uniform microstructure, which helps to expose a large number of active sites and thus improve the alkaline HER catalytic activity.

[0031] (2) The preparation method of the alkaline HER catalyst electrode provided by the application, in step 3), the calcination temperature is 350-450℃, and the calcination time is 2-3h. Using a lower calcination temperature of 350-450℃ can make the diffusion path of the prepared phosphide smaller, so as to lead to more interface areas of the phosphide product.

[0032] (3) The preparation method of the alkaline HER catalyst electrode provided by the application has a simple process and clear flow, and the prepared catalyst electrode has strong catalytic activity and long cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 : Flowchart of the preparation process in Example 1 of this invention;

[0035] Figure 2 XRD pattern of Embodiment 1 of the present invention;

[0036] Figure 3 SEM images of Embodiment 1 of the present invention;

[0037] Figure 4 TEM photographs and dimensional statistics of Embodiment 1 of the present invention;

[0038] Figure 5 The alkaline HER polarization curves and Tafel slopes of Examples 1-3 and Comparative Examples 1-3 of this invention;

[0039] Figure 6 The alkaline HER cycle life of Example 1 of the present invention. Detailed Implementation

[0040] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0041] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0042] The substrate NF (2×2cm) used in the embodiments and comparative examples of the present invention 2 The NF was ultrasonically cleaned for 10 min each with acetone, ethanol, deionized water, 3M HCl and deionized water respectively, and then dried in a vacuum drying oven at 60℃ for 24 h to obtain clean NF.

[0043] Example 1

[0044] This embodiment provides a method for preparing an alkaline HER catalyst electrode, the process flow of which is as follows: Figure 1 As shown, it includes the following steps:

[0045] 1) First, by hydrothermal reaction, 1.5 mmol CoCl2, 1.5 mmol NiCl2 and 6 mmol urea were dissolved in 50 mL of deionized water, and magnetic stirring was performed for 20 min to obtain a transparent pink solution. Next, the mixed solution was poured into a polytetrafluoroethylene reaction kettle lining, and a piece of clean NF was immersed therein. Subsequently, the reaction kettle was kept at 120°C for 6 h, and naturally cooled to room temperature. Finally, the NF was taken out and washed with deionized water and alcohol for 3 times, and dried in a vacuum drying oven at 80°C for 12 h to obtain the precursor.

[0046] 2) Then, by tube furnace calcination annealing, the precursor was loaded into one porcelain boat, and sodium hypophosphite was weighed according to the mass ratio of the precursor to sodium hypophosphite of 1:5 and loaded into another porcelain boat, which were placed at the downstream and upstream of the gas inlet of the tube furnace, respectively, and the temperature was set to increase at a rate of 3°C / min under Ar protection and kept at 350°C for 2 hours. After natural cooling to room temperature, the obtained product was washed with deionized water and alcohol for more than 3 times respectively to completely remove the residual salt, and dried in a vacuum drying oven at 60°C for 12 h to obtain the HER catalyst electrode Ni2P / CoP3@NF.

[0047] Example 2

[0048] The present embodiment provides a preparation method of a basic HER catalyst electrode, comprising the following steps:

[0049] 1) First, by hydrothermal reaction, 2.5 mmol CoCl2, 1.5 mmol NiCl2 and 6 mmol urea were dissolved in 50 mL of deionized water, and magnetic stirring was performed for 20 min to obtain a transparent pink solution. Next, the mixed solution was poured into a polytetrafluoroethylene reaction kettle lining, and a piece of clean NF was immersed therein. Subsequently, the reaction kettle was kept at 150°C for 6 h, and naturally cooled to room temperature. Finally, the NF was taken out and washed with deionized water and alcohol for 5 times, and dried in a vacuum drying oven at 80°C for 24 h to obtain the precursor.

[0050] 2) Then, by tube furnace calcination annealing, the precursor was loaded into one porcelain boat, and sodium hypophosphite was weighed according to the mass ratio of the precursor to sodium hypophosphite of 1:5 and loaded into another porcelain boat, which were placed at the downstream and upstream of the gas inlet of the tube furnace, respectively, and the temperature was set to increase at a rate of 5°C / min under Ar protection and kept at 450°C for 2 hours. After natural cooling to room temperature, the obtained product was washed with deionized water and alcohol for more than 5 times respectively to completely remove the residual salt, and dried in a vacuum drying oven at 80°C for 24 h to obtain the HER catalyst electrode Ni2P / CoP3@NF.

[0051] Example 3

[0052] The present embodiment provides a preparation method of an alkaline HER catalyst electrode, comprising the following steps:

[0053] 1) First, by hydrothermal reaction, 1 mmol CoCl2, 1.5 mmol NiCl2 and 6 mmol urea were dissolved in 50 mL of deionized water, and magnetic stirring was performed for 20 min to obtain a transparent pink solution. Next, the mixed solution was poured into a polytetrafluoroethylene reaction kettle lining, and a piece of clean NF was immersed therein. Subsequently, the reaction kettle was kept at 120°C for 6 h, and naturally cooled to room temperature. Finally, the NF was taken out and washed with deionized water and alcohol for 3 times, and dried in a vacuum drying box at 80°C for 12 h to obtain a precursor.

[0054] 2) Then, by tube furnace calcination annealing, the precursor was loaded into one porcelain boat, and sodium hypophosphite was weighed according to the mass ratio of the precursor to sodium hypophosphite of 1:5 and loaded into another porcelain boat, which were placed at the downstream and upstream of the gas inlet of the tube furnace respectively, and the temperature was set to increase at a rate of 3°C / min under Ar protection and kept at 400°C for 2 hours. After natural cooling to room temperature, the obtained product was washed with deionized water and alcohol for more than 4 times respectively to completely remove the residual salt, and dried in a vacuum drying box at 70°C for 18 h to obtain the HER catalyst electrode Ni2P / CoP3@NF.

[0055] Comparative Example 1

[0056] The present comparative example provides a preparation method of a catalyst electrode, comprising the following steps:

[0057] 1) First, by hydrothermal reaction, 1.5 mmol CoCl2 and 6 mmol urea were dissolved in 50 mL of deionized water, and magnetic stirring was performed for 20 min to obtain a transparent solution. Next, the mixed solution was poured into a polytetrafluoroethylene reaction kettle lining, and a piece of clean NF was immersed therein. Subsequently, the reaction kettle was kept at 120°C for 6 h, and naturally cooled to room temperature. Finally, the NF was taken out and washed with deionized water and alcohol for 3 times, and dried in a vacuum drying box at 80°C for 12 h to obtain a precursor.

[0058] 2) Then, by tube furnace calcination annealing, the precursor was loaded into one porcelain boat, and sodium hypophosphite was weighed according to the mass ratio of the precursor to sodium hypophosphite of 1:5 and loaded into another porcelain boat, which were placed at the downstream and upstream of the gas inlet of the tube furnace respectively, and the temperature was set to increase at a rate of 3°C / min under Ar protection and kept at 350°C for 2 hours. After natural cooling to room temperature, the obtained product was washed with deionized water and alcohol for more than 3 times respectively to completely remove the residual salt, and dried in a vacuum drying box at 60°C for 12 h to obtain the HER catalyst electrode CoP3@NF.

[0059] Comparative Example 2

[0060] The comparative example provides a preparation method of a catalyst electrode, comprising the following steps:

[0061] The CoCl2 in Example 1 is replaced by Co(NO3)2·6H2O, and the remaining steps are the same as those in Example 1 to obtain a Ni2P / CoP3@NF product.

[0062] Comparative Example 3

[0063] The comparative example provides a preparation method of a catalyst electrode, comprising the following steps:

[0064] 6 mg of purchased commercial 20% Pt / C (brand: Macklin, specification: Pt 20%) is dispersed in 550 uL of water / ethanol / 5% Nafion (V / V / V = 250:250:50) solvent, and ultrasonic treatment is performed for 20 min. The prepared catalyst ink is dropped on the NF substrate and naturally air-dried to obtain Pt / C@NF.

[0065] The catalyst electrodes of the examples and comparative examples are subjected to the following tests:

[0066] 1. Structure test

[0067] The catalyst electrodes of the examples and comparative examples are subjected to structure characterization such as XRD, SEM, TEM, and particle size statistics. The test results are as follows:

[0068] Figure 2 is the XRD spectrum of the Ni2P / CoP3@NF in Example 1 of the present application and the pure Ni2P / CoP3 catalyst collected after the NF substrate is dissolved. It can be proved that: because of the shielding effect of the NF substrate, the characteristic peak is not obvious. After the NF is dissolved, the target catalyst containing CoP3 and Ni2P two crystal structures is successfully synthesized by the method.

[0069] Figure 3 is the low-magnification SEM photograph (a) and the high-magnification SEM photograph (b) of Example 1 of the present application. The microstructure of the material is observed by SEM. Because CoP3 and Ni2P have different crystal structures, Co and Ni elements have different diffusion paths during phosphating, thereby forming many fine and dispersed nanoparticle structures. The size of these particles is below 100 nm, and there are a large number of wrinkles on the surface, so the catalyst has a large surface area.

[0070] Figure 4TEM image (a) and particle size statistical histogram (b) of Example 1 of the present application. The internal structure of the material can be seen by TEM, the irregular nanoparticles and clusters observed in SEM, which are also internally stacked by a large number of fine dispersed particles, have a fine particle size of about 16 nm. Due to the extremely small particle size of these particles, it can be inferred that the Ni2P / CoP3@NF contains abundant interface regions, which have a certain regulating effect on its electronic state, adsorption energy and catalytic activity.

[0071] 2. Catalyst performance test

[0072] Electrolytic water catalyst performance evaluation method: cyclic voltammetry test was carried out using a ring disc electrode three-electrode system, the prepared catalyst electrode was used as the working electrode, the Hg|HgO electrode was used as the reference electrode, and the carbon rod was used as the counter electrode. The electrolyte was 1M KOH solution, and H2 was passed into the electrolyte for 20 minutes before HER test, so as to exclude the influence of product dissolved in the electrolyte on the performance.

[0073] The LSV test temperature was room temperature 25℃, the scanning rate was 5mV / s, and the current density-time test curve was carried out at the corresponding overpotential.

[0074] All the LSV curves were iR corrected, and were converted by the reversible hydrogen electrode (RHE) corresponding to the reference electrode, according to the Nernst equation:

[0075] E (RHE) = E (Hg|HgO) + 0.0591 x pH + 0.098 (V)

[0076] Wherein E (Hg|HgO) is the measured potential relative to Hg|HgO, and 0.098V is the standard potential of Hg|HgO at 25℃.

[0077] Figure 5 The HER (a) polarization curve and (b) Tafel slope curve of Example 1-3 and Comparative Example 1-3 in 1M KOH. According to Table 1, Example 1 reaches 10mA cm -2 (η 10 ) only needs an overpotential of 46mV, which is lower than Comparative Example 1 (η 10 = 83mV), Comparative Example 2 (η 10 = 65mV) and Pt / C@NF (η 10 = 58mV). When the current density reaches 100mAcm -2 , the overpotential of the example is lower than Comparative Example 1 (η 100 = 235mV), Comparative Example 2 (η 100= 173 mV) and noble metal catalyst Pt / C@NF (η 100 = 180 mV). The Tafel slope is considered as the basis for judging the speed of catalyst reaction kinetics, and the Tafel slope of Example 1 is 32 mV dec -1 , which is less than Comparative Example 1 (60 mV dec -1 ), Comparative Example 2 (37 mV dec -1 ) and Pt / C@NF (51 mV dec -1 ). The smallest Tafel slope indicates that Example 1 can easily overcome the energy barrier of HER reaction, and has a high energy conversion process. Examples 2 and 3 have the same low overpotential and Tafel slope, and have strong catalytic activity, which can play a good catalytic role.

[0078] Table 1

[0079]

[0080] Figure 6 is the basic HER cycle life curve of Example 1 of the present application. It can be seen that the current density of Example 1 is 97.1% of the initial state after 40h of basic HER constant potential test, which proves that it has excellent cycle stability.

[0081] Obviously, the above examples are only examples for the sake of clarity, and are not limitations on the embodiments. Based on the above description, other different forms of changes or variations can also be made by those of ordinary skill in the art. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for preparing an alkaline HER catalyst electrode, characterized in that, Includes the following steps: 1) Mix CoCl2, NiCl2, urea, and water to obtain a mixed solution; 2) Immerse the nickel foam in the mixed solution from step 1) for a hydrothermal reaction, cool, wash, and dry to obtain the precursor; the nickel foam is sequentially washed with acetone, ethanol, deionized water, hydrochloric acid aqueous solution, and deionized water; the concentration of the hydrochloric acid aqueous solution is 2-3 M HCl; in step 2), the washing is ultrasonic cleaning for 10-15 min. 3) The precursor and sodium hypophosphite were calcined in a protective atmosphere, cooled, washed, and dried to obtain the HER catalyst electrode; The hydrothermal reaction described in step 2) has a reaction temperature of 120-150℃ and a reaction time of 6-8 h; The mass ratio of the precursor to sodium hypophosphite in step 3) is 1:(5-10).

2. The preparation method according to claim 1, characterized in that, The roasting temperature in step 3) is 350-450℃, and the roasting time is 2-3 h.

3. The preparation method according to claim 1 or 2, characterized in that, The heating rate for roasting is 3-5 °C / min.

4. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of CoCl2, NiCl2, and urea is (1-2.5):(1-1.5):6; The ratio of NiCl2 to water is 1.5:(40-60), with units of mol / L.

5. The preparation method according to claim 1 or 2, characterized in that, The protective atmosphere mentioned in step 3) is Ar.

6. The preparation method according to claim 1 or 2, characterized in that, The drying temperature in each step is 60-80℃, and the drying time is 12-24 h.

7. The preparation method according to claim 1 or 2, characterized in that, The washing process in each step involves sequentially washing with water and ethanol. And / or, wash 3-5 times.

8. An alkaline HER catalyst electrode prepared by the preparation method according to any one of claims 1-7.

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