A high-stability transition metal phosphide hydrogen evolution catalyst and a preparation method thereof

Abstract

The present application relates to a kind of high stability transition metal phosphide hydrogen evolution catalyst, which is composed of phosphide active phase and bifunctional metal phosphorus oxide protective layer.The present application also relates to the preparation method of high stability transition metal phosphide hydrogen evolution catalyst, first load metal precursor on foamed nickel, and obtain phosphide catalyst by phosphorization;Then the surface treatment of catalyst is carried out, and the phosphide hydrogen evolution catalyst with phosphorus oxide protective layer is obtained.The protective layer on the surface of the phosphide catalyst of the present application is a "bifunctional" protective layer with simultaneously improved activity and stability, and a uniform protective layer with controllable thickness can be obtained by adjusting the surface treatment conditions during preparation.The preparation process is simple, low in cost, and has important industrial application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrocatalysis and energy materials, and relates to a high-stability transition metal phosphide hydrogen evolution catalyst and a preparation method thereof. BACKGROUND

[0002] In order to meet the large-scale development of hydrogen production by water electrolysis in industry, it is very important to further develop efficient and stable electrocatalysts to realize overall water splitting. In recent years, a large number of studies have been conducted at home and abroad to improve the stability of electrocatalysts, mainly including modification treatment of carbon materials or use of other functional materials as catalyst carriers. The invention patent CN200710157375.9 discloses a method for improving the stability of a fuel cell catalyst, which improves the stability of the carbon carrier by graphitizing the carbon carrier through high-temperature treatment, and further improves the stability of the catalyst. The invention patent CN103413951A prepares a N-doped graphene supported Pt alloy catalyst by introducing N-methyl pyrrolidone as an N source during preparation, which improves the stability of the catalyst to a certain extent. The invention patent CN102945970A improves the stability and conductivity of the carrier by coating a certain thickness of a nitrogen-carbon layer on the surface of the metal oxide nanotube carrier through a nitrogen-carbon source carbonization method. The invention patent CN109994748B improves the stability of the nanoelectrocatalyst by doping N in the carbon-supported noble metal nanoelectrocatalyst. However, the preparation processes of these materials are relatively complex, the cost is high, and the energy consumption is large.

[0003] The currently studied water electrolysis hydrogen evolution catalysts mainly include transition metal borides, carbides, nitrides, sulfides, phosphides, selenides, etc. Among them, transition metal phosphides (TMPs) are widely concerned due to their high natural abundance, low cost, stable catalytic performance, etc. TMPs are a general term for binary, ternary and multi-element phosphides formed by phosphorus elements and transition metal elements (such as Fe, Co, Ni, Cu, Mo, W, etc.), which are generally represented by M x P y TMPs are considered by researchers as one of the most promising alternatives to replace noble metal-based catalysts due to their unique electronic structure and excellent HER and OER catalytic performance. However, their poor durability limits further large-scale application. Designing a protective layer for the catalyst is an effective strategy to improve its stability, but how to achieve uniformity and firmness of the protective layer thickness is the key. If the protective layer thickness is not uniform, local corrosion will occur, affecting the stability of the catalyst; if the protective layer is not firmly combined with the catalyst, it will easily fall off, losing the protective effect on the catalyst. The commonly used deposition method coats metal oxides (such as MnO x), which plays a role in protecting the catalyst. However, such a protective layer often affects the diffusion of the electrolyte, resulting in reduced catalyst activity; in the electrolyte environment, the protective layer formed by deposition is not firmly combined with the catalyst and is easily detached, losing its protective effect. Therefore, it is particularly important to develop a protective layer that can simultaneously improve the electrocatalytic activity and stability of the catalyst to achieve a win-win situation for catalyst activity and stability, but there are few reports on the design of such a "dual-function" protective layer catalyst. SUMMARY

[0004] The first object of the present application is to provide a high-stability transition metal phosphide hydrogen evolution catalyst, which overcomes the problem of poor stability of current transition metal phosphide catalysts by constructing a "dual-function" protective layer that improves the electrocatalytic activity and stability on the surface of the catalyst.

[0005] The second object of the present application is to provide a preparation method of the high-stability transition metal phosphide hydrogen evolution catalyst described above.

[0006] The present application is achieved by the following technical solutions:

[0007] I. A high-stability transition metal phosphide hydrogen evolution catalyst, which is composed of a phosphide active phase and a dual-function metal phosphide oxide protective layer.

[0008] II. A preparation method of the high-stability transition metal phosphide hydrogen evolution catalyst described above, which first loads a metal precursor on a foamed nickel, and then obtains a phosphide catalyst by phosphorization; and then performs surface treatment on the catalyst to obtain a phosphide hydrogen evolution catalyst with a phosphide oxide protective layer.

[0009] Further, the specific steps of the method are as follows:

[0010] (1) The foamed nickel is sequentially washed with 1 mol·L-1 acetone, hydrochloric acid solution and deionized water, and dried for standby use; -1

[0011] (2) The Ni source and the Co source are mixed with NH4F and urea and deionized water to form a homogeneous solution, wherein the molar ratio of Co to Ni is 1-2:1, the molar ratio of NH4F to Co is 4-8:1, the molar ratio of urea to Co is 10-20:1, and the molar ratio of Co to deionized water is 0.001-0.002:1, which is transferred to a reaction kettle containing a vertically placed foamed nickel, and a hydrothermal reaction is carried out at 120-160℃ for 6-12 hours, and then washed with ethanol and deionized water alternately for 3 times after cooling to room temperature, and dried to obtain a catalyst precursor;

[0012] ​(3) the catalyst precursor and P source are placed in two quartz boats respectively, the molar ratio of P source and Ni source is 3-6:1, then the quartz boats are placed in a tube furnace, phosphorization is carried out at 350 DEG C for 2 hours in inert gas, the heating rate is 2 DEG C·min -1 , the phosphorization treatment is carried out, and the NiCoP hydrogen evolution catalyst is obtained;

[0013] (4) after the temperature of the tube furnace is reduced to 50-100 DEG C, the air valve is opened, the oxygen content in the inert gas is adjusted to 0.5-10v%, the treatment time is 1-2 hours, and the NiCoP@Ni x Co y P z O h hydrogen evolution catalyst is obtained after being reduced to room temperature.

[0014] Further, the Ni source is any one of nickel chloride, nickel nitrate and nickel acetate.

[0015] Further, the Co source is any one of cobalt chloride, cobalt nitrate and cobalt acetate.

[0016] Further, the P source is any one of ammonium hypophosphite and sodium hypophosphite.

[0017] Further, the inert gas in step (4) is N2 gas or Ar gas.

[0018] The positive effect of the above technical solution is that the phosphide catalyst surface of the application has a dual functional protective layer, which avoids direct contact between the catalyst active phase NiCoP and the electrolyte, the Ni x Co y P z O h protective layer is relatively stable in the electrolyte environment, which can significantly improve the stability of the catalyst; first, the P atom with multiple valence states and high negative electricity in Ni x Co y P z O h can regulate the electronic structure and stabilize the reaction intermediate, so the Ni x Co y P z O h protective layer itself has good catalytic activity; secondly, the Ni x Co y P z O hThe protection layer can further improve the hydrogen evolution activity of the NiCoP catalyst through the electronic interaction of the heterostructure interface formed with the NiCoP active phase. Therefore, the protection layer constructed in the present application is a "dual-function" protection layer capable of improving activity and stability simultaneously; the preparation process can obtain a protection layer with controllable thickness and uniformity through the regulation of surface treatment conditions, and the preparation process is simple and low in cost, the protection layer grown in situ is combined with the catalyst through a chemical bond, the combination is firm and not easy to fall off; the method can be widely applied to various important electrochemical reactions such as water decomposition, carbon dioxide reduction and microbial fuel cell, and has important industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 NiCoP@Ni x Co y P z O h / NF catalyst preparation process;

[0020] Figure 2 NiCoP@Ni x Co y P z O h / NF catalyst XRD pattern;

[0021] Figure 3 NiCoP@Ni x Co y P z O h / NF catalyst TEM pattern;

[0022] Figure 4 NiCoP@Ni x Co y P z O h / NF catalyst protection layer formation and characteristic diagram;

[0023] Figure 5 NiCoP@Ni x Co y P z O h / NF catalyst hydrogen evolution LSV curve;

[0024] Figure 6 NiCoP@Ni x Co y P z O h / NF catalyst stability curve. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be further described below in combination with specific examples, but should not be understood as limiting the present application. Example 1

[0026] The foam nickel was sequentially washed with 1 mol·L-1 of acetone, hydrochloric acid solution and deionized water, and dried for standby. Nickel chloride, cobalt nitrate, NH4F, urea and deionized water (molar ratio of Ni, Co, NH4F, urea, deionized water was 1:1:8:10:1000) were mixed to form a uniform solution, which was transferred to a reaction kettle containing vertically placed foam nickel, and hydrothermal reaction was carried out at 120℃ for 12 hours. After cooling to room temperature, it was washed with ethanol and deionized water alternately for 3 times, and dried to obtain a Ni-Co bimetallic precursor; the obtained precursor and amine hypophosphite were respectively placed in two quartz boats, and the molar ratio of amine hypophosphite to nickel chloride was 3:1. Then the quartz boats were placed in a tube furnace, and phosphorization was carried out at 350℃ for 2 hours under nitrogen protection atmosphere, and the heating rate was 2℃·min-1. After phosphorization treatment, a NiCoP / NF catalyst was obtained. After cooling to 100℃, the oxygen valve was opened, the oxygen content in nitrogen was adjusted to 10%, and the surface treatment was carried out for 1h. Then the temperature was lowered to room temperature to obtain a NiCoP@NiCoPO4 / NF catalyst (see -1 -1 x y z h Figure 1 ).

[0027] The NiCoP@NiCoPO4 / NF catalyst obtained in this example was characterized by XRD, and the results are shown in x y z h

[0028] The NiCoP@NiCoPO4 / NF catalyst obtained was characterized by XRD, and the active phase in the catalyst was analyzed and tested. The results (see x y z h Figure 2 ), characteristic peaks appeared near 2θ = 44.5°, 51.9° and 76.5°, which belonged to the (111), (200), (220) crystal faces of the foam nickel (PDF #70-0989). The characteristic peaks located at 2θ = 40.9°, 44.9°, 47.3° and 54.4° belonged to the NiCoP phase, which were NiCoP (111), (201), (210) and (300) crystal faces (PDF #71-2336), indicating that the active phase in the catalyst was NiCoP. Example 2

[0029] ​​​​​​​​​​​​​​The foamed nickel was washed with 1 mol·L -1 of acetone, hydrochloric acid solution and deionized water in sequence, and dried for standby. Nickel nitrate, cobalt nitrate, NH4F, urea, deionized water (molar ratio of Ni, Co, NH4F, urea, deionized water was 1:1:4:20:500) were mixed to form a uniform solution, which was transferred to a reaction kettle containing vertically placed foamed nickel, and hydrothermal reaction was carried out at 160℃ for 6 hours. After cooling to room temperature, it was washed with ethanol and deionized water alternately for 3 times, and dried to obtain a Ni-Co bimetallic precursor; the obtained precursor and sodium hypophosphite were placed in two quartz boats respectively, and the molar ratio of sodium hypophosphite to nickel nitrate was 6:1. Then the quartz boats were placed in a tube furnace, and phosphorization was carried out at 350℃ for 2 hours under nitrogen protection atmosphere, and the heating rate was 2℃·min -1 . After phosphorization treatment, the NiCoP / NF catalyst was obtained. After cooling to 50℃, the oxygen valve was opened, the oxygen content in nitrogen was adjusted to 0.5%, and the surface treatment was carried out for 2 hours. Then the NiCoP@Ni x Co y P z O h / NF catalyst was obtained after cooling to room temperature.

[0030] TEM characterization of the NiCoP@Ni x Co y P z O h / NF catalyst obtained in this example:

[0031] TEM characterization results of the obtained NiCoP@Ni x Co y P z O h / NF catalyst are shown in Figure 3 (a). A uniform protective layer with a thickness of about 4 nm was formed on the surface of the catalyst, and the active phase of the catalyst NiCoP and the Ni x Co y P z O h protective layer formed a heterostructure. Example 3

[0032] The foamed nickel was washed with 1 mol·L -1acetate, NH4F, urea, deionized water (molar ratio of Ni, Co, NH4F, urea, deionized water is 1:2:9:15:1000), mixed to form a uniform solution, which is transferred to a reaction kettle containing a vertically placed foam nickel, and hydrothermal reaction is carried out at 160℃ for 6 hours, and after cooling to room temperature, it is washed with ethanol and deionized water alternately for 3 times, and dried to obtain a Ni-Co bimetallic precursor; the obtained precursor and amine hypophosphite are respectively placed in two quartz boats, the molar ratio of amine hypophosphite to nickel acetate is 4:1, and then the quartz boats are placed in a tube furnace, and phosphorization is carried out at 350℃ for 2 hours under nitrogen protection atmosphere, the heating rate is 2℃·min -1 , the phosphorization treatment is carried out to obtain a NiCoP / NF catalyst, the temperature is lowered to 50℃, the oxygen valve is opened, the oxygen content in nitrogen is adjusted to 0.5%, the surface treatment is carried out for 2h, and then the temperature is lowered to room temperature to obtain a NiCoP@Ni x Co y P z O h / NF catalyst.

[0033] The NiCoP@Ni x Co y P z O h / NF catalyst obtained in this example is characterized by TEM:

[0034] TEM characterization results of the obtained NiCoP@Ni x Co y P z O h / NF catalyst are shown in Figure 3 (b). The protective layer with uniform thickness is formed on the surface of the catalyst, and the thickness is about 2 nm. It can be seen that the thickness of the protective layer can be controlled by adjusting the surface treatment conditions. In addition, this protective layer, because M-P is a chemical bond, after surface treatment, the Ni x Co y P z O h is obtained by inserting O in the NiCoP on the surface of the catalyst, so it is very firm combined with the catalyst and is not easy to fall off, and forms a uniform coating, which plays a good protective role (see Figure 4 ). It is shown that the catalyst protective layer is firmly combined with the catalyst active phase, the protective layer is uniform, and the thickness is controllable. Example 4

[0035] The foam nickel is sequentially washed with 1 mol·L -1acetone, hydrochloric acid solution and deionized water, and dried for standby. Nickel nitrate, cobalt nitrate, NH4F, urea, deionized water (molar ratio of Ni, Co, NH4F, urea, deionized water is 1:1:5:15:500) were mixed to form a uniform solution, which was transferred to a reaction kettle containing a vertically placed foam nickel, and hydrothermal reaction was carried out at 120℃ for 6 hours, and after cooling to room temperature, it was washed with ethanol and deionized water alternately for 3 times, and dried to obtain a Ni-Co bimetallic precursor; the obtained precursor and amine hypophosphite were respectively placed in two quartz boats, the molar ratio of amine hypophosphite to nickel nitrate was 5:1, and then the quartz boats were placed in a tube furnace, and phosphorization was carried out at 350℃ for 2 hours under nitrogen protection atmosphere, the heating rate was 2℃·min -1 , the phosphorization treatment was carried out to obtain a NiCoP / NF catalyst, the temperature was lowered to 50℃, the oxygen valve was opened, the oxygen content in nitrogen was adjusted to 5%, and after surface treatment for 2 hours, the temperature was lowered to room temperature to obtain a NiCoP@Ni x Co y P z O h / NF catalyst.

[0036] For comparison, a NiCoP / NF catalyst was prepared: other conditions were the same as the preparation method of the NiCoP@Ni x Co y O z / NF catalyst, except that after phosphorization, it was directly cooled to room temperature.

[0037] The hydrogen evolution catalytic activity of the NiCoP@Ni x Co y O z / NF catalyst obtained in the example and the NiCoP / NF without protective layer was determined:

[0038] The linear sweep voltammetry (LSV) was tested by using a typical three-electrode system to evaluate the hydrogen evolution (HER) catalytic activity of the catalyst in 1.0 M KOH solution, and the results are shown in Figure 5 . It can be seen from Figure 5 that under alkaline conditions, the overpotential η 10 of the NiCoP / NF catalyst is 100 mV, the overpotential η x of the NiCoP@Ni y Co z O 10 catalyst with a protective layer is only 54 mV, which is reduced by 46%, indicating that after adding the protective layer, the activity of the catalyst is further improved. The protective layer can improve the activity of the catalyst, which can be explained in two aspects. First, the Ni x Co y P z O hThe multivalent, highly electronegative P atoms can regulate the electronic structure and stabilize the intermediates of the hydrogen evolution reaction, thus exhibiting hydrogen evolution catalytic activity; in addition, Ni x Co y P z O h The protective layer forms a heterostructure with the NiCoP active phase, and through the electronic interactions at the interface of the heterostructure, it can further improve the hydrogen evolution activity of the NiCoP catalyst. Example 5

[0039] The nickel foam was successively treated with 1 mol∙L⁻¹ -1 Wash with acetone, hydrochloric acid solution, and deionized water, and dry for later use. Mix nickel chloride, cobalt chloride, NH4F, urea, and deionized water (molar ratio of Ni, Co, NH4F, urea, and deionized water is 1:1.5:8:20:1000) to form a homogeneous solution. Transfer this solution to a reactor containing vertically placed nickel foam and hydrothermally react at 120°C for 8 hours. After cooling to room temperature, wash three times alternately with ethanol and deionized water, and dry to obtain the Ni-Co bimetallic precursor. Place the obtained precursor and sodium hypophosphite in two separate quartz boats (molar ratio of sodium hypophosphite to nickel chloride is 3:1). Place the quartz boats in a tube furnace and phosphate at 350°C for 2 hours under a nitrogen atmosphere, with a heating rate of 2°C·min. -1 Phosphating was performed to obtain NiCoP / NF catalyst. The temperature was lowered to 50 °C, the oxygen valve was opened, and the oxygen content in the nitrogen was adjusted to 5 v%. After surface treatment for 2 h, the temperature was lowered to room temperature to obtain NiCoP@Ni x Co y P z O h / NF catalyst.

[0040] To make comparisons, NiCoP / NF catalysts were prepared: other conditions were compared with NiCoP@Ni x Co y O z The preparation method for / NF catalysts is the same, except that after phosphating, they are directly cooled to room temperature.

[0041] The NiCoP@Ni obtained in this embodiment x Co y O z Determination of the hydrogen evolution catalytic stability of / NF catalyst and unprotected NiCoP / NF:

[0042] In a 1.0 M KOH solution, the hydrogen evolution stability of the catalyst was evaluated by comparing the changes in the LSV curve after 3000 cycles in a typical three-electrode system. The results are shown in [Figure number missing]. Figure 6 (a). As can be seen from the figure, NiCoP@Nix Co y O z The difference between the hydrogen evolution LSV curve of the NiCoP / NF catalyst and the initial state is much smaller than that of the NiCoP / NF catalyst, indicating that the stability of the catalyst is improved after the protective layer is added. Figure 6 (b). As can be seen from the figure, the NiCoP@Ni x Co y O z The NiCoP@Ni x Co y O z The protective layer can significantly improve the stability of the catalyst.

[0043] The phosphide catalyst of the present application has a Ni x Co y O z The protective layer can significantly improve the stability of the catalyst. x Co y P z O h The protective layer is relatively stable in the electrolyte environment, which can significantly improve the stability of the catalyst; therefore, in combination with Example 4, the Ni x Co y O z The protective layer has a dual role of improving the activity and stability of the catalyst, and belongs to a "dual-function" protective layer; the preparation process can be controlled by surface treatment conditions to obtain a protective layer with controllable thickness and uniformity, and the preparation process is simple and low in cost, the in-situ grown protective layer is combined with the catalyst through a chemical bond, which is firm and not easy to fall off; the method can be widely applied to various important electrochemical reactions such as water splitting, carbon dioxide reduction, microbial fuel cell, etc., and has important industrial application value.

Claims

1. A method for preparing a highly stable transition metal phosphide hydrogen evolution catalyst, the catalyst comprising a phosphide active phase and a bifunctional metal phosphorus oxide protective layer, characterized in that: First, a metal precursor is loaded onto nickel foam and phosphated to obtain a phosphide catalyst. Then, the catalyst surface is treated to obtain a phosphide hydrogen evolution catalyst with a phosphorus oxide protective layer. The specific steps of this method are as follows: (1) The nickel foam was successively treated with 1 mol∙L -1 Wash with acetone, hydrochloric acid solution and deionized water, then dry and set aside. (2) Ni source and Co source are mixed with NH4F and urea and deionized water to form a homogeneous solution, wherein the molar ratio of Co to Ni is 1-2:1, the molar ratio of NH4F to Co is 4-8:1, the molar ratio of urea to Co is 10-20:1, and the molar ratio of Co to deionized water is 0.001-0.002:

1. The solution is transferred to a reactor containing vertically placed nickel foam and subjected to hydrothermal reaction at 120-160℃ for 6-12 hours. After cooling to room temperature, the solution is washed three times alternately with ethanol and deionized water and dried to obtain the catalyst precursor. (3) The catalyst precursor and the P source were placed in two quartz boats respectively, with a molar ratio of P source to Ni source of 3-6:

1. The quartz boats were then placed in a tube furnace and phosphated at 350 °C for 2 hours in an inert gas atmosphere at a heating rate of 2 °C·min. -1 Phosphating is performed to obtain NiCoP hydrogen evolution catalyst; (4) After the temperature of the tube furnace is reduced to 50~100℃, the air valve is opened, the oxygen content in the inert gas is adjusted to 0.5-10 v%, the treatment time is 1-2 hours, and the temperature is reduced to room temperature to obtain NiCoP@Ni. x Co y P z O h Hydrogen evolution catalyst.

2. The preparation method according to claim 1, characterized in that: The Ni source is any one of nickel chloride, nickel nitrate, or nickel acetate.

3. The preparation method according to claim 1, characterized in that: The Co source is any one of cobalt chloride, cobalt nitrate, or cobalt acetate.

4. The preparation method according to claim 1, characterized in that: The P source is either ammonium hypophosphite or sodium hypophosphite.

5. The preparation method according to claim 1, characterized in that: In step (4), the inert gas is N2 or Ar.

Images