CN113725452B

CN113725452B - Hexagonal close-packed nickel and polycrystalline phase nickel heterojunction electrocatalyst, preparation method and application

Info

Publication number: CN113725452B
Application number: CN202110980726.6A
Authority: CN
Inventors: 罗威; 李芸博; 苏立新
Original assignee: SUZHOU Institute OF WUHAN UNIVERSITY
Current assignee: SUZHOU Institute OF WUHAN UNIVERSITY
Priority date: 2021-08-25
Filing date: 2021-08-25
Publication date: 2023-04-04
Anticipated expiration: 2041-08-25
Also published as: CN113725452A

Abstract

The invention provides a close-packed hexagonal nickel and polycrystalline phase nickel heterojunction electrocatalyst, a preparation method and application thereof. Firstly, nickel acetylacetonate is taken as a precursor, oleylamine is taken as a solvent, anhydrous glucose is taken as a surfactant, a close-packed hexagonal nickel precursor is synthesized in an organic solution by a simple colloidal method, and then annealing is carried out in a reducing atmosphere to prepare the close-packed hexagonal/face-centered cubic nickel heterostructure electrocatalyst, namely the polycrystalline phase nickel heterojunction electrocatalyst. The catalyst can simultaneously optimize the combination energy of hydrogen and oxyhydrogen species and reduce the formation energy of water through mutual adjustment of interface electronic structures, thereby having excellent hydroxidizing performance, and having great application prospect in the field of alkaline medium hydroxidizing reaction. The invention also provides two preparation methods for preparing the face-centered cubic nickel with different sizes.

Description

Hexagonal close-packed nickel and polycrystalline phase nickel heterojunction electrocatalyst, preparation method and application

Technical Field

The invention relates to the technical field of electrocatalyst preparation, in particular to a close-packed hexagonal nickel, face-centered cubic nickel and polycrystalline phase nickel heterojunction electrocatalyst, a preparation method and application thereof.

Background

Hydrogen is considered one of the most promising carriers of clean energy due to its environmental protection and high energy density. Utilization of hydrogen by fuel cell technology is a key component in achieving low carbon hydrogen-emitting economy. Compared to proton exchange membrane fuel cells, alkaline exchange membrane fuel cells are receiving much attention due to their potential to use non-platinum group metal catalysts. To date, considerable research has been devoted to the development of non-platinum group metal electrocatalysts having performance comparable to standard platinum-based catalysts for cathode oxygen reduction reactions in alkaline exchange membrane fuel cells. However, the catalytic activity of platinum-based electrocatalysts for anodic oxidation reactions is about 2 orders of magnitude lower in alkaline electrolytes than in acidic electrolytes, resulting in greatly increased platinum-based metal loadings in alkaline exchange membrane fuel cells. Therefore, it is necessary to find a highly efficient and stable non-platinum group metal electrocatalyst for the hydrogen oxidation reaction in an alkaline medium.

Currently, the most effective non-platinum group metal alkaline hydrogen oxidation electrocatalysts are limited to nickel-based nanocatalysts. The catalytic performance of nickel-based nanocatalysts is still far lower than that of platinum group metal-based catalysts, probably due to their relatively strong hydrogen binding energy. More importantly, it has been reported that the formation of interfacial water molecules is the potential determining step of the alkaline hydrogen oxidation reaction. Therefore, current research continues to maximize efforts to optimize hydrogen binding energy and or to promote hydrogen and oxygen species binding energy. In recent years, extensive research has been conducted on nickel-based electrocatalysts, which have been developed with controllable composition, size, shape and defect structure, and in order to further improve catalytic performance, various approaches have been explored, including alloying or recombination with other metals, support from carbon-based materials, doping with interstitial heteroatoms (e.g., doping of the lattice of nickel with B and N atoms), strain engineering, and building heterostructures.

However, conventional strategies have been limited primarily to the modification of face centered cubic nickel and face centered cubic nickel based alloys, which may be limited by inherent reactivity and stability. In contrast, phase engineering provides another effective way to promote catalytic performance by effectively reducing the formation energy of metastable crystalline phases and adjusting atomic interface electronic structure, while its effect on hydrogen oxidation reactions is rarely explored, and therefore, the synthesis of polycrystalline phase nickel heterojunction catalysts remains a great challenge.

A publication by Zhisen Li et al entitled "Hexagonal Nickel as a high purity Durable and Active catalyst for Hydrogen Evolution" discloses a crystalline heterogeneous structured Nickel catalyst having an inner backbone of face-centered cubic phase and a surface covered by a thin layer of Hexagonal close-packed (hcp) phase. However, the nickel catalyst has the defects that the hexagonal close-packed phase is only coated on the surface, the proportion of the face-centered cubic phase to the hexagonal close-packed phase cannot be regulated, the pure-phase hexagonal close-packed phase cannot be successfully prepared, and the alkaline hydrogen oxidation reaction is not tested, so that the root cause of regulation of the activity of the catalyst cannot be researched.

In view of the above, there is a need to design an improved hexagonal close-packed nickel, face-centered cubic nickel, and polycrystalline nickel heterojunction electrocatalyst, and a preparation method and applications thereof, so as to solve the above problems.

Disclosure of Invention

The invention aims to provide a heterojunction electrocatalyst made of close-packed hexagonal nickel, face-centered cubic nickel and polycrystalline phase nickel, a preparation method and application thereof.

In order to achieve the above object, the present invention provides a method for preparing a polycrystalline phase nickel heterojunction electrocatalyst, comprising the steps of:

s1, preparing close-packed hexagonal nickel nanoparticles by a colloid method;

s2, dispersing the close-packed hexagonal nickel nanoparticles and the carbon carrier prepared in the step S1 in an organic solvent, carrying out ultrasonic treatment for 1-4 h, then carrying out centrifugal collection and vacuum drying treatment to obtain a mixture; and then placing the mixture in a reducing atmosphere, and calcining for 0.5-2 h at a calcining temperature higher than 250 ℃ and lower than 600 ℃ to obtain the close-packed hexagonal/face-centered cubic nickel heterojunction, namely the polycrystalline phase nickel heterojunction electrocatalyst.

As a further improvement of the present invention, in step S1, a specific preparation method of the hexagonal close-packed nickel nanoparticles comprises:

mixing nickel acetylacetonate, glucose and oleylamine according to a predetermined proportion, stirring and heating to 50-80 ℃ to form a uniform mixed solution, blowing by using nitrogen, and keeping the temperature for 0.5-2 hours; and then gradually heating to 150-250 ℃, keeping for 1-3 h, cooling, washing, centrifuging and carrying out post-treatment to prepare the hexagonal close-packed nickel nanoparticles.

As a further improvement of the invention, the proportion of the nickel acetylacetonate, the glucose and the oleylamine is (0.01-3) mmol: (100-600) g: (0.05-10) mL.

As a further improvement of the invention, the calcination temperature is 250-550 ℃;

the reducing atmosphere includes, but is not limited to, a hydrogen/nitrogen mixed reducing atmosphere or a hydrogen/argon mixed reducing atmosphere. .

As a further improvement of the invention, the carbon carrier is one of XC-72 carbon carrier, activated carbon, graphene, reduced graphene oxide, acetylene black and carbon nano tubes;

the organic solvent includes but is not limited to one or more of ethanol, n-hexane, ethanol, chloroform and acetone.

In order to realize the purpose, the invention also provides the polycrystalline phase nickel heterojunction electrocatalyst prepared by the preparation method of the polycrystalline phase nickel heterojunction electrocatalyst. The polycrystalline phase nickel heterojunction electrocatalyst has an atom accumulation structure of face-centered cubic abcabc 8230and close-packed hexagonal abab 8230.

In order to realize the purpose, the invention also provides the application of the polycrystalline phase nickel heterojunction electrocatalyst in the field of alkaline medium hydrogen oxidation reaction.

In order to achieve the above object, the present invention further provides a method for preparing hexagonal close-packed nickel, which adopts a colloid method, and comprises the following steps:

a1, mixing nickel acetylacetonate, glucose and oleylamine according to (0.01-3) mmol: (100-600) g: (0.05-10) mL, stirring and heating to 50-80 ℃ to form a uniform mixed solution, blowing with nitrogen, and keeping the temperature for 0.5-2 h;

and A2, gradually heating to 150-250 ℃, keeping for 1-3 h, cooling, washing, centrifuging and carrying out post-treatment to prepare the hexagonal close-packed nickel nanoparticles.

In order to achieve the above object, the present invention further provides a method for preparing face-centered cubic nickel, comprising the following steps:

p1, preparing the close-packed hexagonal nickel nanoparticles by a colloid method; the specific preparation method of the hexagonal close-packed nickel nanoparticles comprises the following steps:

mixing nickel acetylacetonate, glucose and oleylamine according to a predetermined ratio, stirring and heating to 50-80 ℃ to form a uniform mixed solution, blowing by using nitrogen, and keeping the temperature for 0.5-2 hours; then gradually heating to 150-250 ℃, keeping for 1-3 h, cooling, washing, centrifuging and post-treating to prepare the close-packed hexagonal nickel nanoparticles;

p2, dispersing the close-packed hexagonal nickel nanoparticles prepared in the step P1 and a carbon carrier in an organic solvent, carrying out ultrasonic treatment for 1-4 h, then carrying out centrifugal collection and vacuum drying treatment to obtain a mixture; and calcining the mixture in the reducing atmosphere at the calcining temperature of 600 ℃ or above for 0.5 to 2 hours to obtain the face-centered cubic nickel nanoparticles.

In order to realize the purpose, the invention also provides the face-centered cubic nickel prepared by the preparation method of the face-centered cubic nickel, and the particle size of the face-centered cubic nickel reaches more than 50nm.

mixing nickel acetate, glucose and oleylamine according to a predetermined ratio to obtain a mixed solution, stirring and heating to 60 ℃ to form a uniform solution, blowing with nitrogen, keeping the temperature for 0.5-2 h, gradually heating to 150-250 ℃, keeping the temperature for 1-3 h, cooling, washing, centrifuging and carrying out post-treatment to obtain the face-centered cubic nickel nanoparticles.

As a further improvement of the invention, the proportion of the nickel acetate, the glucose and the oleylamine is (0.01-3) mmol: (100-600) g: (0.05-10) mL.

In order to realize the purpose, the invention also provides the face-centered cubic nickel prepared by the preparation method of the face-centered cubic nickel, and the particle size of the face-centered cubic nickel is higher than 20nm and lower than 50nm.

The invention has the beneficial effects that:

1. the preparation method of the polycrystalline phase nickel heterojunction electrocatalyst provided by the invention comprises the steps of firstly, taking nickel acetylacetonate as a precursor, oleylamine as a solvent and anhydrous glucose as a surfactant, synthesizing a close-packed hexagonal nickel precursor in an organic solution by a simple colloidal method, then annealing under mixed gas of nitrogen/hydrogen atmosphere, and realizing the phase transformation process of converting the close-packed hexagonal nickel precursor into a close-packed hexagonal/face-centered cubic nickel heterostructure or face-centered cubic nickel by regulating and controlling the annealing (calcining) temperature, thereby further realizing the optimization of the electronic structure of the interface of the polycrystalline phase nickel heterojunction.

2. The invention provides polycrystalline phase nickelThe preparation method of the heterojunction electrocatalyst adopts simple phase control synthesis to prepare the Ni catalyst with the close-packed hexagonal/face-centered cubic nickel heterostructure, and the mass activity of the prepared close-packed hexagonal/face-centered cubic nickel catalyst under 50mV is 12.28mAmg _Ni ^-1 6 times of the face-centered cubic nickel catalyst, and has higher durability and carbon monoxide tolerance under an alkaline medium. The combination of experimental analysis and theoretical calculation finds that the improvement of the hydrogen oxidation performance of the phase engineering nickel catalyst comes from mutual adjustment of interface electronic structures, so that the adsorption energy of hydrogen and oxyhydrogen species is optimized, and the generation energy of water species is reduced.

3. The preparation method of the polycrystalline phase nickel heterojunction electrocatalyst provided by the invention provides a simple two-step strategy, and polycrystalline phase interface nickel is synthesized in 0.1M KOH electrolyte, has excellent hydrogen oxidation performance, and can be used as an excellent electrocatalyst of a hydrogen oxidation reaction. The phase-controlled synthesis method for preparing the polycrystalline catalyst is a feasible way for stabilizing a metastable-state material, avoids the technical defect that extra impurities are introduced into the catalyst in the prior art through doping, and is beneficial to accurately regulating and controlling an atomic interface through a modified electronic structure and reaction kinetics so as to improve the catalytic activity of the electrocatalyst.

4. The polycrystalline phase nickel heterojunction electrocatalyst provided by the invention has two crystal phase structures of face-centered cubic nickel and close-packed hexagonal nickel, and can simultaneously optimize the binding energy of hydrogen and oxyhydrogen species and reduce the formation energy of water through mutual adjustment of interface electronic structures, so that the electrocatalyst has excellent hydrogen oxidation performance.

5. When the loading capacity of the anode metal is 0.4mgcm, the polycrystalline phase nickel heterojunction electrocatalyst provided by the invention ^-2 At 80 deg.C and 0.2Mpa back pressure, the hcp/fcc-Ni catalyst prepared by the invention can reach 0.19Wcm ^-2 (Current Density 0.4Acm ^-2 ) The peak power of (a) is a very low loading for the Ni-based catalyst, indicating that the anode catalyst hcp/fcc-Ni prepared by the present invention may have a higher activity.

6. The face-centered cubic nickel provided by the invention can be prepared into face-centered cubic nickel nanoparticles with different sizes by different preparation methods, and has the advantages of simple and controllable preparation process and huge application prospect.

Drawings

FIG. 1 is an electron micrograph and a size distribution of hexagonal close-packed nickel (hcp-Ni) provided in example 1 of the present invention (a is 50nm on the scale of the drawing; b is 100nm on the scale of the drawing).

FIG. 2 is an electron micrograph and a size distribution plot (scale in a is 50nm; scale in b is 100 nm) of a hexagonal close-packed/face-centered cubic nickel heterojunction hcp/fcc-Ni (hcp-300) provided in example 2 of the present invention.

FIG. 3 is an electron micrograph and a size distribution of face centered cubic nickel (fcc-Ni-600) provided in example 3 of the present invention (a in the figure is 50nm; b in the figure is 100 nm).

FIG. 4 is an electron micrograph and a size distribution chart of face-centered cubic nickel (fcc-Ni) provided in example 4 of the present invention (scale bar of a in the figure is 50nm; scale bar of b in the figure is 100 nm).

FIG. 5 is an electron micrograph and a size distribution plot (scale a in the figure is 50nm; scale b in the figure is 100 nm) of a hexagonal close-packed/face-centered cubic nickel heterojunction (hcp-400) provided in example 5 of the present invention.

FIG. 6 is an electron micrograph and a size distribution plot (scale a in the figure is 50nm; scale b in the figure is 100 nm) of a hexagonal close-packed/face-centered cubic nickel heterojunction (hcp-500) provided in example 6 of the present invention.

FIG. 7 is an XRD pattern for examples 1-3 and 5-6 of the present invention.

FIG. 8 is a schematic view showing the interface between face-centered cubic nickel and hexagonal close-packed nickel in examples 2-3 and 5-6 of the present invention.

Fig. 9 is a microscopic image of the hexagonal close-packed/face-centered cubic nickel heterojunction hcp/fcc-Ni provided in example 2 of the present invention (fig. 9 (a) is a high-resolution transmission electron microscope image of hcp/fcc-Ni; fig. 9 (b) is an enlargement of the orange dotted line region in (a) and an atomic stacking order of face-centered cubic nickel; fig. 9 (C) is a HAADF-STEM image of hexagonal nickel; and fig. 9 (d) is a hcp/fcc-Ni and Ni (green), C (red) and overlapping energy dispersive x-ray (EDX) mapping.

FIG. 10 is an XRD pattern of the electrocatalyst provided in inventive examples 1-2 and 4 (in FIG. 10, (f) is a powder x-ray diffraction pattern of hexagonal-face-centered nickel, hexagonal-close-packed nickel and hcp/fcc-Ni. In FIG. 10, (g) is a partially enlarged XRD pattern of hcp/fcc-Ni).

FIG. 11 is a high resolution Ni 2p XPS spectra of electrocatalyst hexagonal face-centered nickel, hexagonal close-packed nickel and hcp/fcc-Ni provided in inventive examples 1-2 and 4.

FIG. 12 is an XPS spectrum of hcp/fcc-Ni for 1s of Ni and 2p of C provided by the present invention. FIG. 13 is a graph showing the performance characteristics of the hydrogen oxidation reaction of the electrocatalysts provided in examples 1-2 and 4 provided by the present invention in a hydrogen-saturated 0.1MKOH electrolyte (FIG. 13 (a) shows that face-centered hexagonal nickel, hexagonal close-packed nickel and hcp/fcc-Ni are saturated with hydrogen in 0.1M KOH at a scan rate of 5mV s ^-1 HOR polarization curve at 2500 rpm. FIG. 13 (b) is a polarization curve of hcp/fcc-Ni in 0.1M KOH saturated hydrogen solution at a scan rate of 5mV s ^-1 The rotating speed is 2500-400 rpm; FIG. 13 (c) is a Tafel plot derived from (a) and its corresponding fit to the Butler-Volmer equation; in FIG. 13, (d) is j for three catalysts at an overpotential of 50mV ^k And j ⁰ Comparison of (d).

FIG. 14 shows the hydrogen saturation in 0.1M KOH at a scan rate of 5mV s for examples 2-3 and 5-6 of the present invention ^-1 HOR polarization curve at 2500 rpm.

FIG. 15 is a K-L plot (vs. RHE) at 50mv of hcp/fcc-Ni provided by example 2 of the present invention.

FIG. 16 is a CV plot of hcp-Ni (a), fcc-Ni (b) and hcp/fcc-Ni (c) in Ar saturated 0.1M KOH as provided in examples 1-2 and 4 of the present invention, scanned at a rate of 50mV s ^-1 。

FIG. 17 shows CV curves of hcp-400 (a), hcp-500 (b), hcp-600 (c) in Ar saturated 0.1M KOH at a scan rate of 50mV s, provided in examples 3 and 5-6 of the present invention ^-1 。

FIG. 18 is a linear fitted polarization curve simplified by the Butler-Volmer equation for examples 1-2 and 4 of the present invention.

FIG. 19 is a graph of hydrogen oxidation of electrocatalysts provided in examples 1-2 and 4 of the present invention in argon-saturated 0.1M KOH electrolytesThe reaction performance was characterized (FIG. 19 (a) is hexagonal face-centered nickel, hexagonal close-packed nickel and hcp/fcc-Ni in 0.1M KOH saturated with argon at a scanning speed of 50mV s ^-1 CV of (a); FIG. 19 (b) is a CO curve for hexagonal face-centered nickel, hexagonal close-packed nickel, and hcp/fcc-Ni catalysts; FIG. 19 (C) is a chronoamperometric curve of 2 wt% Pt/C and hcp/fcc-Ni in a 0.1KOH solution measured under saturated hydrogen conditions containing 100ppm CO; FIG. 19 (d) is a polarization curve of 2 wt% Pt and hcp/fcc-Ni before and after the chronoamperometry test).

FIG. 20 shows the CV curves of the electrocatalysts provided in examples 1-2 and 4) of the invention in Ar saturated 0.1M KOH at a scan rate of 50mV s ^-1 。

Fig. 21 is a chemical stability characterization diagram of the electrocatalyst provided in example 2 of the present invention (fig. 21 (a) is a polarization curve around 1000 cycles CV, and fig. 21 (b) is a CV curve around 1000 CV).

FIG. 22 is a TEM image of the electrocatalyst provided in example 2 of the present invention after HOR stability testing in 0.1M KOH solution.

Fig. 23 is an XRD pattern of the electrocatalyst provided in example 2 of the invention after HOR stability experiments in 0.1M KOH solution.

FIG. 24 is a graph showing the characterization of the catalytic activity of the electrocatalyst according to example 2 of the present invention (FIG. 24 (a) is a band diagram of the Ni 3d orbital and the O2 p orbital on hcp/fcc-Ni; FIG. 24 (b) is a d-orbital local DOS on pure hexagonal close-packed nickel and hcp/fcc-Ni; FIG. 24 (c) is a d-orbital local DOS on pure hexagonal face-centered nickel and hcp/fcc-Ni; FIG. 24 (d) is a free energy diagram of the adsorption of H on pure hexagonal face-centered nickel, pure hexagonal close-packed nickel and hcp/fcc-Ni; FIG. 24 (e) is the adsorption energy of OH on pure hexagonal face-centered nickel, pure hexagonal close-packed nickel and hcp/fcc-Ni; FIG. 24 (f) is the adsorption energy of H and OH to form H ₂ The energy barrier of O).

FIG. 25 shows the optimized structures of (a) pure face-centered cubic nickel (111), (b) pure close-packed hexagonal nickel (001), (c) face-centered cubic (111) nickel/close-packed hexagonal nickel (001), and (d) close-packed hexagonal nickel (001)/face-centered cubic nickel (111) in examples 1-2 and 4 of the present invention.

FIG. 26 is a band diagram of the three-dimensional orbitals of Ni and O2 p on pure face-centered cubic nickel, pure hexagonal close-packed nickel and hcp/fcc-Ni in examples 1-2 and 4 of the present invention.

FIG. 27 is a graph showing the differential charge density at the hcp/fcc-Ni interface in example 2 of the present invention.

FIG. 28 is a graph showing the optimal adsorption sites of hydrogen on pure face-centered cubic nickel, pure hexagonal close-packed nickel and hcp/fcc-Ni in examples 1-2 and 4 of the present invention.

FIG. 29 is a graph showing the optimal adsorption sites of OH on pure face-centered cubic nickel, pure hexagonal close packed nickel and hcp/fcc-Ni in examples 1-2 and 4 of the present invention.

FIG. 30 is a graph of cell voltage and power density versus current density for the single cell APEFCs test for the hcp/fcc-Ni/C catalyst prepared in example 2 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.

It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the solution of the present invention are shown in the drawings, and other details not closely related to the present invention are omitted.

In addition, it should be further noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention provides a preparation method of a polycrystalline phase nickel heterojunction electrocatalyst, which comprises the following steps:

s1, preparing close-packed hexagonal nickel nanoparticles by a colloid method;

s2, dispersing the close-packed hexagonal nickel nanoparticles and the carbon carrier prepared in the step S1 in an organic solvent, carrying out ultrasonic treatment for 1-4 h, then carrying out centrifugal collection and vacuum drying treatment to obtain a mixture; and then placing the mixture in a reducing atmosphere, and calcining for 0.5-2 h at the calcining temperature of more than 250 ℃ and less than 600 ℃ to obtain the close-packed hexagonal/face-centered cubic nickel heterojunction, namely the polycrystalline phase nickel heterojunction electrocatalyst.

Preferably, in step S1, the specific preparation method of the hexagonal close-packed nickel nanoparticles comprises:

mixing nickel acetylacetonate, glucose and oleylamine according to a predetermined ratio, stirring and heating to 50-80 ℃ to form a uniform mixed solution, blowing by using nitrogen, and keeping the temperature for 0.5-2 hours; and then gradually heating to 150-250 ℃, keeping for 1-3 h, cooling, washing, centrifuging and carrying out post-treatment to prepare the hexagonal close-packed nickel nanoparticles.

Preferably, the ratio of the nickel acetylacetonate to the glucose to the oleylamine is (0.01 to 3) mmol: (100-600) g: (0.05-10) mL.

Preferably, the calcining temperature is 250-550 ℃;

Preferably, the carbon carrier is one of XC-72 carbon carrier, activated carbon, graphene, reduced graphene oxide, acetylene black and carbon nano tubes;

Example 1

Embodiment 1 provides a method for preparing a hexagonal close-packed nickel electrocatalyst, comprising the steps of:

s1, synthesis of hexagonal close-packed nickel:

in general, 135mg of nickel acetylacetonate, 600mg of glucose and 10mL of oleylamine were put into a two-necked flask and stirred, and the mixture was heated to 60 ℃ to form a uniform solution, purged with nitrogen gas, kept at the reaction temperature for 1 hour, gradually heated to 190 ℃ at a rate of 10 ℃/min, and kept for 2 hours. And washing the cooled product by using n-hexane and ethanol to remove impurities for at least 3 times, and centrifugally collecting at 9800rpm to prepare the hexagonal close-packed nickel nanoparticles as shown in figure 1.

Example 2

Embodiment 2 provides a method for preparing a polycrystalline phase nickel heterojunction electrocatalyst, comprising the following steps:

s1, synthesis of hexagonal close-packed nickel:

S2, synthesis of a close-packed hexagonal/face-centered cubic nickel heterojunction:

and (3) dispersing the hexagonal close-packed nickel nanoparticles prepared in the step (S1) and XC-72R carbon black in an ethanol solution, and carrying out ultrasonic treatment for 2 hours. The product was collected by centrifugation at 9500rpm and dried in a vacuum desiccator. Finally, the sample is calcined for 1 hour at 300 ℃ in a hydrogen/nitrogen mixed reducing atmosphere to obtain a close-packed hexagonal/face-centered cubic nickel heterostructure, namely the polycrystalline phase nickel heterojunction electrocatalyst, as shown in fig. 2.

Example 3

Embodiment 3 provides a method for preparing face-centered cubic nickel, comprising the steps of:

s1, synthesis of hexagonal close-packed nickel:

in general, 135mg of nickel acetylacetonate, 600mg of glucose and 10mL of oleylamine were put into a two-necked flask and stirred, and the mixture was heated to 60 ℃ to form a uniform solution, purged with nitrogen gas, kept at the reaction temperature for 1 hour, gradually heated to 190 ℃ at a rate of 10 ℃/min and kept for 2 hours. And washing the cooled product by using n-hexane and ethanol to remove impurities for at least 3 times, and centrifugally collecting at 9800rpm to prepare the hexagonal close-packed nickel nanoparticles.

S2, synthesizing face-centered cubic nickel:

and (3) dispersing the hexagonal close-packed nickel nanoparticles prepared in the step (S1) and XC-72R carbon black in an ethanol solution, and carrying out ultrasonic treatment for 2 hours. The product was collected by centrifugation at 9500rpm and dried in a vacuum desiccator. Finally, the sample was calcined at 600 ℃ for 1 hour in a hydrogen/nitrogen mixed reducing atmosphere to obtain face centered cubic nickel nanoparticles, as shown in fig. 3.

Example 4

Embodiment 4 provides a method for preparing face-centered cubic nickel, comprising the steps of:

128mg of nickel acetate, 600mg of glucose and 10mL of oleylamine were put into a two-necked flask and stirred, the mixture was heated to 60 ℃ to form a uniform solution, and then purged with nitrogen gas, the reaction temperature was maintained for 1 hour, and the mixture was gradually heated to 190 ℃ at a rate of 10 ℃/min and maintained for 2 hours. And washing the cooled product by using n-hexane and ethanol to remove impurities for at least 3 times, and centrifugally collecting at 9800rpm to prepare the face-centered cubic nickel nanoparticles as shown in figure 4.

Examples 5 to 6

The difference from example 1 is that: the calcination temperature was varied, and the other steps were the same as in example 1, and the polycrystalline phase nickel heterojunction electrocatalyst obtained was as shown in fig. 5 and 6, respectively.

Table 1 shows the calcination temperature settings of examples 1 and 5 to 6

Examples	Calcination temperature
		Example 1	300℃
Example 5	400℃
		Example 6	500℃

1. The physical and chemical properties of the electrocatalysts prepared in examples 1 to 6 were analyzed:

a Transmission Electron Microscope (TEM) image of the hexagonal close-packed nickel prepared in example 1, as shown in fig. 1, can be seen to have a good distribution of hexagonal close-packed nickel with an average grain size of 31.43nm.

A Transmission Electron Microscope (TEM) image of the polycrystalline nickel heterojunction electrocatalyst prepared in example 2 is shown in fig. 2, and it can be seen that during the annealing (calcination) process the hexagonal close-packed nickel nanoparticle precursors were converted to hexagonal close-packed/face-centered cubic nickel heterojunction nanoparticles at a calcination temperature of 300 ℃, which were spherical, good individually, and approximately 31.91nm in diameter.

A Transmission Electron Microscope (TEM) image of the face centered cubic nickel prepared in example 3 is shown in fig. 3, and it can be seen that the hexagonal nickel nanoparticle precursor in close packing is converted into face centered cubic nickel nanoparticles at a calcination temperature of 600 ℃ during annealing (calcination), the average particle diameter is about 51.77nm, and the particle size shows a tendency to become larger.

Transmission Electron Microscopy (TEM) images of face centered cubic nickel prepared in example 4 as shown in fig. 4, example 3 was synthesized using hexagonal close packed nickel of 29.04nm average size using nickel acetate as a nickel source in addition to nickel acetate as a nickel source in a similar manner to example 1 to eliminate the effect of sintering of the particles caused by high temperature calcination.

A Transmission Electron Microscope (TEM) image of the polycrystalline nickel heterojunction electrocatalyst prepared in example 5 is shown in fig. 5, and it can be seen that the hexagonal close packed/face centred nickel heterojunction nanoparticles, which are spherical and have a diameter of about 28.97nm, are converted from the hexagonal close packed nickel nanoparticle precursor at a calcination temperature of 400 ℃ during the annealing (calcination).

Transmission Electron Microscope (TEM) images of the polycrystalline nickel heterojunction electrocatalyst prepared in example 6 are shown in fig. 6, and it can be seen that the hexagonal close-packed nickel nanoparticle precursor was converted into hexagonal close-packed/face-centered cubic nickel heterojunction nanoparticles having a spherical shape with a diameter of about 33.46nm at a calcination temperature of 500 ℃ during annealing (calcination).

Referring to the XRD pattern shown in fig. 7, it can be seen that the hexagonal close-packed nickel precursors of examples 2 and 5-6 can be transformed into hexagonal close-packed/face-centered cubic nickel heterostructures, labeled hcp-300, hcp-400, hcp-500, respectively, by adjusting the annealing (calcination) temperature; the XRD results showed that both face-centered cubic phase and hexagonal close-packed phase were observed.

Referring to FIG. 8, a schematic diagram of the interface between face-centered cubic nickel (fcc-Ni) and hexagonal close-packed nickel (hcp-Ni) is shown, which shows that under the preparation and synthesis method provided by the present invention, phase transition of nickel is realized at different annealing and calcination temperatures, and the transition from hexagonal close-packed nickel (hcp-Ni) to face-centered cubic nickel (fcc-Ni) and hexagonal close-packed nickel (hcp-Ni) heterojunction is changed to face-centered cubic nickel (fcc-Ni).

The crystalline phase structure of the polycrystalline nickel heterojunction electrocatalyst prepared in example 2 is shown in fig. 9.

The High Resolution TEM (HRTEM) image shown in fig. 9 (a) shows the interface between two different phases (indicated by white dashed lines) in the electrocatalyst prepared in example 2. 0.203nm is well matched with the (111) plane spacing of the face-centered cubic nickel, 0.203nm and 0.217nm are well matched with the (011) plane spacing and the (002) plane spacing of the close-packed hexagonal nickel, and the intersection angle is 62 degrees. The face centered cubic nickel structure is further determined by the atomic stacking order of abcabcabc (as shown in (b) of fig. 9).

In addition, the atomic packing order of ABABAB was also observed, confirming the formation of a hexagonal close-packed nickel structure, as shown in (c) of fig. 9. The energy dispersive x-ray spectroscopy (EDX) elemental mapping as shown in (d) of fig. 9 shows a uniform distribution of Ni elements on the carbon layer.

As shown in fig. 10 (f), characteristic peaks near 39.1 °, 41.5 °, 44.5 °, 58.4 °, 71.0 °, and 78.0 ° may be labeled as hexagonal close packed nickel. Additional peaks at 44.5 °, 51.8 °, and 76.4 ° may correspond to the crystalline phase of face centered cubic nickel. In a partial enlargement of the XRD spectrum of the hexagonal close packed/face centered cubic nickel heterojunction prepared in example 2, coexistence of two phases can be clearly seen, as shown in (g) of fig. 10.

Example 3 nanoparticles of face centered cubic nickel (fcc-Ni-600) can be obtained by a phase transition process of annealing a hexagonal close packed nickel precursor at 600 deg.C. In FIG. 10, (f) is an XRD spectrum of fcc-Ni-600, and three peaks are located near 44.5 °, 51.8 ° and 76.4 ° respectively, corresponding to the (111), (200) and (220) planes of face centered cubic nickel.

Referring to fig. 11 and 12, the present inventors further investigated the surface structures and electronic states of hexagonal close-packed/face-centered cubic nickel of example 2, hexagonal close-packed nickel of example 1, and face-centered cubic nickel of example 4 using X-ray photoelectron spectroscopy (XPS). 2p of nickel _3/2 The XPS spectrum of (A) shows that the main valences of nickel in hexagonal close-packed nickel and face-centered cubic nickel are 0 valences, positive valences (855.6 eV ), and the peak of about 855.6eV belongs to NiO, possibly being a product of surface partial oxidation in the atmosphere. Due to the surface structure transformation of the two different crystalline phases, hexagonal close packed/hexagonal close packed nickel inevitably has a rich interface between the hexagonal close packed nickel and the hexagonal close packed nickel, which may be caused by the transfer of electrons from the hexagonal close packed nickel to the hexagonal close packed nickel near the interface.

2. The performance analysis was carried out on the electrocatalysts prepared in examples 1 to 6:

1. first, the hydrogen oxidation reaction performance of all electrocatalysts was studied in hydrogen saturated 0.1M KOH electrolyte by a rotating disk electrode system, as shown in figures 13 to 18.

As shown in fig. 13 (a) and 14, the hexagonal close-packed/face-centered cubic nickel (hcp-300) prepared in example 2 showed the highest hydrogen oxidation performance in all samples tested, highlighting the key role of the phase engineering in improving the hydrogen oxidation performance of the nickel-based catalyst.

FIG. 13 (b) is a hydrogen oxidation polarization curve of hexagonal close-packed/face-centered cubic nickel at a rotation speed of 2500 to 400 rpm. According to the ICP-AES result, the mass activity of the hexagonal close packed/face centered cubic nickel at 50mV, normalized by the mass of nickel, is 12.28mAmg _Ni ^-1 Is far better than the close-packed hexagonal nickel (2.96 mAmg) _Ni ^-1 ) And face centered cubic nickel (2.08 mAmg) _Ni ^-1 ). Notably, the resulting hexagonal close packedThe mass activity of the/face-centered cubic nickel electrocatalyst is 4 times and 6 times higher than that of the close-packed hexagonal nickel and the face-centered cubic nickel respectively. This value is higher than most reported nickel-based oxyhydroxide electrocatalysts. The exchange current density can be calculated according to the Butler-Volmer equation as shown in fig. 13 (c) and fig. 15.

J for hexagonal close packed/face centered cubic nickel normalized by electrochemically active surface area (ECSA) (fig. 16 and 17) ^0,s The value was about 30.88. Mu. Acm _Ni ^-2 Respectively, hexagonal nickel (9.54 μ Acm) _Ni ^-2 ) And face centered cubic nickel (11.87 μ Acm) _Ni ^-2 ) About 3 times (fig. 13 (d)).

As shown in FIG. 18, j can also be estimated from-10 mV to 10mV by linearly fitting polarization curves simplified by the Butler-Volmer equation ⁰ The numerical value of (c).

2. Cyclic Voltammograms (CVs) of the three catalysts in argon saturated 0.1M KOH electrolyte, as shown in fig. 19 and 20, reveal typical characteristic peaks of nickel.

As shown in fig. 20, the anode peak at 0.287V for the hexagonal close-packed/face-centered cubic nickel prepared in example 2 (hcp/fcc-Ni) was more electropositive than the anode peaks for the hexagonal close-packed nickel of example 1 (0.291V) and the face-centered cubic nickel of example 4 (0.296V), indicating a change in the catalyst surface electron interactions, consistent with the XPS results (as shown in fig. 11).

When the electrolyte is saturated with argon, the anode current density is negligible. The current density at the anode of the hexagonal close packed/face centered cubic nickel of example 2 started to rise at-0V when the electrolyte was saturated with hydrogen and increased significantly with increasing overpotential, indicating that the current was contributed by hydrogen oxidation. In addition, since the adsorbed hydroxide species promoted the removal of carbon monoxide, carbon monoxide stripping experiments were also conducted to monitor the catalyst surface for hydroxide species binding. Fig. 20 (b) shows that the peak of carbon monoxide elution of the hexagonal close packed/face centered cubic nickel catalyst is lower than that of the hexagonal close packed and face centered cubic nickel, indicating that the enhanced binding energy of the hydroxide species on the hexagonal close packed/face centered cubic nickel is also likely to be the cause of the enhanced performance of the hydroxide.

Since the current industrial production of hydrogen relies mainly on the conversion of hydrocarbons to natural gas, this may result in the inevitable carbon monoxide content of the final hydrogen. Therefore, carbon monoxide tolerance is a desirable criterion when finding an effective electrocatalyst in a hydrogen fuel cell. As shown in fig. 20 (C), long-term electrocatalysis of close-packed hexagonal/face-centered cubic nickel in hydrogen saturated 0.1M KOH with 100ppm carbon monoxide at 0.05v vs. rhe, compared to Pt/C (20 wt%), it is evident that close-packed hexagonal/face-centered cubic nickel maintains a relatively stable current density in the chronoamperometric test, while the anodic current density of Pt/C is significantly reduced. The hydrogen oxidation polarization curve shows that the activity of Pt/C is rapidly reduced, and the reduction range of the activity of the close-packed hexagonal/face-centered cubic nickel is smaller, which indicates that the close-packed hexagonal/face-centered cubic nickel has better carbon monoxide tolerance than Pt/C.

The stability of the hexagonal close-packed/face-centered cubic nickel is researched by adopting an accelerated tolerance test (ADT), and the potential range is-0.08-0.42V. As shown in fig. 21, the polarization curve and specific activity did not vary much. The characteristics of TEM, XRD and the like after ADT are shown in figures 22-23, which proves that the morphology and the crystal phase of the hexagonal close-packed/face-centered cubic nickel are kept well, and further shows that the hexagonal close-packed/face-centered cubic nickel has good stability.

3. And (3) further exploring the reason of the superior catalytic performance of the phase-controlled engineering nickel catalyst by adopting Density Functional Theory (DFT) calculation.

For face-centered cubic nickel and hexagonal close-packed nickel, the surface was developed in the (111) and (001) directions, and the hexagonal close-packed (001)/face-centered cubic nickel (111) interface was constructed according to the best-matched lattice, and the specific calculation results are shown in fig. 25 and table 2.

Table 2 Total energy of two heterojunction interfaces

Model	Totalenergy(eV)
		fcc/hcp-Ni	-359.719
hcp/fcc-Ni	-359.504

First, the relative electronic structure calculation is carried out on the energy bands and the local state density of face centered cubic nickel, close-packed hexagonal nickel and close-packed hexagonal/face centered cubic nickel under the action of different adsorbents. As shown in fig. 24 (a) and fig. 26, the rise of the 3d orbital of the nickel atom in the hexagonal close-packed phase can provide more unoccupied 3d orbital to accommodate the electron of the O atom, thereby promoting the interaction of the Ni atom and the O atom in the adsorbed oxyhydrogen species. In hexagonal close packed/face centered cubic nickel, the adsorption strength of the adsorbed oxyhydrogen species to the face centered cubic phase is weaker than that of the face centered cubic nickel. As shown in (b) to (c) of fig. 24, a negative shift (-1.32 eV) in the center of the d band in the face-centered cubic phase and a positive shift (-1.16 eV) in the center of the d band in the hexagonal close packed phase indicate that the adsorption strength of adsorbed hydrogen decreases in the face-centered cubic phase and increases in the hexagonal close packed phase. As can be further seen from the interface charge density distribution shown in fig. 27, the interface charge distribution is significant, contributing to the improvement of the catalytic performance.

Free energy of hydrogen adsorption (. DELTA.G) _H* ) Is widely regarded as a descriptor for determining the catalytic activity of the HOR electrocatalyst, and the optimal value is deltaG _H* =0eV, indicating that the adsorption strength of hydrogen is neither too strong nor too weak. As shown in FIG. 24 (d) and FIG. 28, the hexagonal close-packed/face-centered cubic nickel has Δ G _H* = 0.05eV, more thermally neutral than face-centered cubic nickel (-0.24 eV) and hexagonal close-packed nickel (0.28 eV).

The binding strength of the adsorbed hydroxide species on different surfaces was further examined (the optimized adsorption structure is shown in FIG. 29). As shown in (e) of fig. 24, the strength of adsorbed hydroxide species of the hexagonal close-packed phase in hexagonal close-packed/face-centered cubic nickel was significantly enhanced compared to the strength of pure face-centered cubic nickel and hexagonal close-packed nickel, which is consistent with the carbon monoxide stripping test.

As shown in (f) of fig. 24, the hexagonal close packed/face centered cubic nickel has a good water formation process with an energy barrier of 0.58eV, which is much lower than that of face centered cubic nickel (0.78 eV) and hexagonal close packed (0.83 eV).

These results indicate that the formation of a hexagonal close packed/face centered cubic interface optimizes the adsorption energy of hydrogen and oxyhydrogen species, promotes the water generation process, and further enhances the activity of HOR in alkaline media.

3. The electrocatalyst prepared in example 2 was subjected to a single cell test:

the catalyst hcp/fcc-Ni prepared in example 2, a commercial catalyst Pt/C (Johnson-Matthey) was used as a cathode catalyst. The catalysts hcp/fcc-Ni/C and Pt/C of example 2 were mixed with homemade QAPT ionomer (20 mgmL-1) respectively in acetone solvent to form acetone mixed solution, wherein the catalyst accounts for 80wt%, and the ionomer accounts for 20wt%. The acetone mixed solution was then sonicated for 40min, and then sprayed onto QAPPPT APEs (25. + -. 3 μm, in the dry state) to form a catalyst-coated membrane (CCM) with an electrode area of 4cm ^-2 . The metal loading of both the cathode and anode was 0.4mgcm ^-2 。

H at a temperature of 80 DEG C ₂ /O ₂ And testing single-cell APEFCs. H ₂ And O ₂ Humidification treatment (100% RH) was carried out at 80 ℃ at a flow rate of 1000sccm and a back pressure of 0.2MPa on both sides. The fuel cell was activated at a constant current for a period of time and the cell voltage was then recorded at each current density.

The cell test results were as follows:

the cell voltage and power density versus current density plot of the hcp/fcc-Ni catalyst prepared in example 2 of the present invention in the APEFCs single cell test is shown in FIG. 30.

As shown in FIG. 30, when the loading of the anode metal is 0.4mgcm ^-2 At 80 deg.C and 0.2MPa back pressure, the hcp/fcc-Ni catalyst prepared in example 2 can reach 0.19Wcm ^-2 (Current Density 0.4Acm ^-2 ) Is very low loading for the Ni-based catalyst, indicating that the anode catalyst prepared in example 2 was usedhcp/fcc-Ni may have higher activity.

It is important to note that in other embodiments of the present invention, other ratios of nickel acetylacetonate/nickel acetate, glucose and oleylamine may be used to prepare hexagonal close packed nickel and cubic face centred nickel, all of which can successfully prepare the above described electrocatalysts.

In the invention, the influence of the ratio of nickel acetylacetonate to nickel acetate, glucose and oleylamine on the hexagonal close-packed nickel and the cubic face-centered nickel prepared by the invention is as follows:

the selection of different nickel sources can adjust and control the preparation of different crystalline phases for nickel acetylacetonate or nickel acetate, and the proportion of glucose and oleylamine has influence on the appearance, particle size and growth rate of the prepared catalyst.

In conclusion, the invention provides a close-packed hexagonal nickel and polycrystalline phase nickel heterojunction electrocatalyst, a preparation method and application thereof. Firstly, nickel acetylacetonate is taken as a precursor, oleylamine is taken as a solvent, anhydrous glucose is taken as a surfactant, a close-packed hexagonal nickel precursor is synthesized in an organic solution by a simple colloidal method, and then annealing is carried out in a reducing atmosphere to prepare the close-packed hexagonal/face-centered cubic nickel heterostructure electrocatalyst, namely the polycrystalline phase nickel heterojunction electrocatalyst. The catalyst can simultaneously optimize the combination energy of hydrogen and oxyhydrogen species and reduce the formation energy of water through mutual adjustment of interface electronic structures, thereby having excellent hydroxidizing performance, and having great application prospect in the field of alkaline medium hydroxidizing reaction.

The invention also provides two preparation methods for preparing the face-centered cubic nickel with different sizes. Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention.

Claims

1. A preparation method of a polycrystalline phase nickel heterojunction electrocatalyst is characterized by comprising the following steps: the method comprises the following steps:

s1, preparing close-packed hexagonal nickel nanoparticles by a colloid method;

s2, dispersing the close-packed hexagonal nickel nanoparticles prepared in the step S1 and a carbon carrier in an organic solvent, carrying out ultrasonic treatment for 1 to 4 hours, then carrying out centrifugal collection and vacuum drying treatment to obtain a mixture; then placing the mixture in a reducing atmosphere, and calcining for 0.5 to 2h at a calcining temperature higher than 250 ℃ and lower than 600 ℃ to obtain a close-packed hexagonal/face-centered cubic nickel heterojunction, namely a polycrystalline phase nickel heterojunction electrocatalyst;

in step S1, the specific preparation method of the hexagonal close-packed nickel nanoparticles comprises:

mixing nickel acetylacetonate, glucose and oleylamine according to a predetermined ratio, stirring and heating to 50-80 ℃ to form a uniform mixed solution, blowing by using nitrogen, and keeping the temperature for 0.5-2h; then gradually heating to 150 to 250 ℃, keeping for 1 to 3h, cooling, washing, centrifuging, and then processing to prepare the hexagonal close-packed nickel nanoparticles;

the proportion of the nickel acetylacetonate to the glucose to the oleylamine is (0.01 to 3) mmol: (100 to 600) g: (0.05 to 10) mL;

the polycrystalline phase nickel heterojunction electrocatalyst has an atomic stacking structure of abcabc 8230of a face-centered cubic phase and abab 8230of a close-packed hexagonal phase.

2. The method of preparing a polycrystalline phase nickel heterojunction electrocatalyst according to claim 1, wherein: the calcination temperature is 250-550 ℃;

the reducing atmosphere is a hydrogen/nitrogen mixed reducing atmosphere or a hydrogen/argon mixed reducing atmosphere.

3. The method of preparing a polycrystalline phase nickel heterojunction electrocatalyst according to claim 1, wherein: the carbon carrier is one of XC-72 carbon carrier, activated carbon, graphene, acetylene black and carbon nano tubes;

the organic solvent is one or more of ethanol, n-hexane, chloroform and acetone.

4. A method of making a polycrystalline phase nickel heterojunction electrocatalyst according to claim 1, wherein: and (3) increasing the calcination temperature to 600 ℃ or above, and calcining for 0.5 to 2h to obtain the face-centered cubic nickel nanoparticles with the particle size of more than 50nm.

5. A polycrystalline phase nickel heterojunction electrocatalyst prepared according to the method of any one of claims 1 to 3, wherein: the polycrystalline phase nickel heterojunction electrocatalyst has an atomic stacking structure of abcabcabc 8230of face-centered cubic and abab 8230of close-packed hexagonal phase.

6. Use of a polycrystalline phase nickel heterojunction electrocatalyst according to any one of claims 1 to 3 or according to claim 5, wherein said catalyst is prepared by a method comprising the steps of: the polycrystalline phase nickel heterojunction electrocatalyst is applied to the field of alkaline medium hydrogen oxidation reaction.