CN112076763A - Ni/Ni3S2Nanocluster-graphene composite material and preparation method and application thereof - Google Patents

Abstract

The invention discloses a Ni/Ni ₃ S ₂ nano-cluster-graphene composite material, a preparation method thereof, and an application in electrocatalytic oxygen evolution. Bacteria (Pandoraea sp.B‑6, deposit number CGMCC No.4239) were regulated by changing the composition of the medium to accumulate CdS nanoparticles on the cell membrane, which were used as carriers to load graphene oxide (GO) and Ni ²⁺ in turn by electrostatic adsorption. To form a composite precursor, and then prepare a catalyst through one-step pyrolysis, the preparation method is simple, convenient, safe, cheap and easy to control. The material has excellent OER catalytic activity, low reaction energy barrier, more active sites, high electrochemically active surface area, superior electrical conductivity to improve electron transfer efficiency, and can be used in long-term catalytic processes. Maintaining high catalytic performance and high stability, it can replace precious metals to promote the development of electrolyzed water systems in alkaline media.

Description

A kind of Ni/Ni3S2 nano-cluster-graphene composite material and its preparation method and application

technical field

The invention belongs to the technical field of catalyst preparation, in particular to a Ni/Ni ₃ S ₂ nano-cluster-graphene composite material, a preparation method thereof, and an application in electrocatalytic oxygen evolution.

Background technique

Growing global energy consumption requires a sustainable energy supply. Water splitting devices initiated by oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are highly regarded as ideal next-generation energy storage or conversion technologies. Compared with HER, the inherently complex four-electron transfer process of OER has been the biggest limitation to improve the overall water splitting efficiency. To accelerate this complex process, there is an urgent need to develop efficient and stable OER electrocatalysts. To date, the most recognized and effective and stable OER catalysts in acidic or basic media are still based on noble metal oxides, such as IrO ₂ and RuO ₂ . However, the high cost and scarcity of highly active noble metal-based catalysts seriously hinder their large-scale applications.

Efforts are currently underway to explore earth-abundant non-precious metal electrocatalysts, especially supported transition metal catalysts such as first-row (3d) transition metal oxides, sulfides, selenides, phosphides, and double-layer hydroxides Wait. These precious metal-substituting catalysts have attracted increasing interest in renewable energy research. Among these materials, nickel-based compounds, especially for nickel sulfide (Ni ₃ S ₂ ), are considered to be one of the most widely studied OER catalytic materials due to their promising OER performance and cost-effectiveness. Despite the good electrochemical performance, the low electrical conductivity and the limited number of exposed active sites inherently hinder the improvement of its potential catalytic performance.

In addition, elemental nickel nanoparticles are also one of the widely studied electrocatalytic materials. However, due to their structural size and surface activity, the electrochemical stability is poor. However, the prepared elemental nickel composites are mostly used in HER catalysts and rarely involve OER systems.

Graphene-based electrocatalytic materials, benefiting from their inherent high surface area and offering a large number of active centers, are considered promising candidates for various energy conversion and storage systems. However, due to the inherent high Fermi level of graphene, a high applied voltage is inevitably required for the graphene catalyst to activate oxygen intermediates.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the purpose of the present invention is to provide a Ni/Ni ₃ S ₂ nanocluster-graphene composite material and its preparation method and application, which are induced to form in the pyrolysis process by a method mediated by biological deposition. The ultra-small-sized elemental Ni and Ni ₃ S ₂ coupled nanoclusters were anchored on the graphene substrate, which showed high stability and high catalytic activity in OER catalysis.

The present invention is a Ni/Ni ₃ S ₂ nano-cluster-graphene composite material. The composite material is composed of a graphene matrix and Ni/Ni ₃ S ₂ nano-clusters uniformly fixed on the graphene matrix.

Preferably, the Ni/Ni ₃ S ₂ nanoclusters are formed by chemical coupling of Ni and Ni ₃ S ₂ .

In the Ni/Ni ₃ S ₂ nano-cluster-graphene composite material provided by the present invention, the Ni/Ni ₃ S ₂ nano-clusters are embedded in the graphene layer and uniformly fixed on the graphene matrix, and the Ni/Ni ₃ S 2 nano-clusters are embedded in the graphene layer. The ₂ nanoclusters are composed of elemental Ni and Ni ₃ S ₂ , which are chemically coupled to form composite nanoclusters. The coupling of the heterointerface causes a certain degree of lattice disorder in the dual-phase material, increasing more active sites. At the same time, by introducing 3d transition metal ions as strong electron acceptors, the Fermi level of graphene is reduced, which can effectively reduce the energy difference between the σ state and the graphene Fermi level, thereby reducing the electron transfer in graphene. potential barrier, improve the electrical conductivity of the material, and ultimately improve the electrocatalytic performance of the composite. In addition, the support of the graphene matrix also enhances the stability of the catalyst.

Preferably, the diameter of the Ni/Ni ₃ S ₂ nanocluster is 10 nm˜100 nm. In the present invention, the particle size distribution of Ni/Ni ₃ S ₂ nanoclusters is very uniform, and most of them are about 30 nm.

A preparation method of a Ni/Ni ₃ S ₂ nano-cluster-graphene composite material of the present invention comprises the following steps:

(1) bacteria are inoculated in the sterile medium containing Cd, after culturing, solid-liquid separation obtains CdS-bacterial precursor;

(2) The CdS-bacteria precursor obtained in step (1) is loaded with graphene oxide (GO) and Ni ²⁺ in turn by electrostatic adsorption, and a sandwich-type CdS-bacteria/GO/Ni composite precursor is obtained by solid-liquid separation and drying. body;

(3) The CdS-bacteria/GO/Ni composite precursor obtained in step (2) is placed in a protective atmosphere for pyrolysis treatment, and the obtained pyrolysis product is the Ni/Ni ₃ S ₂ nanocluster-graphene composite material.

In step (1) of the present invention, the CdS-bacterial precursor refers to bacteria that accumulate CdS nanoparticles. The biologically deposited CdS is uniformly distributed in the periplasmic space of the bacterial cell membrane in the form of nanocrystals. On the one hand, CdS acts as a sulfur source to realize the in-situ sulfidation of Ni ²⁺ , the in-situ synthesized Ni ₃ S ₂ and the reduced metal Ni element. The composite nanoclusters formed by chemical coupling are anchored on graphene, and on the other hand, pores are created by the formation of Cd vapors during pyrolysis to optimize the structure of the composites.

Preferably, the bacteria in the step (1) are bacteria with sulfide synthesis ability.

In the present invention, there is no need to limit the bacterial species in step (1), for example, the bacteria with sulfide synthesis ability reported in the prior art can be used, such as Pseudomonas, Escherichia coli, Shewanella .

Preferably, the bacterium is Pandoraea sp. B-6 with the deposit number of CGMCC No.4239.

In the present invention, the used Pandoraea sp. B-6 with the deposit number of CGMCC No. 4239 is the strain that the inventor has self-preserved and published public documents.

Preferably, in step (1), the culturing conditions of the bacteria are 2-10% of the inoculum, the temperature is 25-40° C., the natural pH conditions, and the culturing time is 20-36 h.

Further preferably, the culture conditions of the bacteria are 10% of the inoculum, the temperature is 30°C, the natural pH conditions, and the culture time is 24h.

Preferably, in step (1), the molar concentration of Cd ²⁺ in the Cd-containing sterile medium is 0.2-0.5 mM, preferably 0.3-0.4 mM, more preferably 0.4 mM.

In the present invention, it is found through research that the concentration of Cd ²⁺ in the culture medium significantly affects the growth of bacteria and the accumulation of CdS nanoparticles, thereby affecting the content of Ni ₃ S ₂ in the final composite material. Bacterial growth was unaffected and the accumulated CdS content increased with increasing Cd 2+ concentration when the Cd ²⁺ concentration increased from 0.2 mM to 0.4 mM, but the bacterial tolerance to Cd was exceeded when the Cd ²⁺ concentration increased to 0.5 mM The CdS content of bacteria was the highest and the electrocatalytic performance of the final product was the best when the Cd ²⁺ concentration was 0.4 mM.

Preferably, in step (1), the mode of described solid-liquid separation is centrifugal separation, and the rotating speed of centrifugal separation is 6500-8500rpm, and the time is 3-10min.

Preferably, the Cd-containing sterile medium in step (1) is a sterile medium with glucose as the sole carbon source, and its components are glucose 2g/L, Cd(NO ₃ ) ₂ 0.2-0.5mM, NH ₄ Cl 1.5 g/L, MgCl ₂ 0.2 g/L, CaCl ₂ 0.01 g/L, FeSO ₄ ·7H ₂ O 0.015 g/L, MnSO ₄ ·H ₂ O 0.01 g/L; MOPs 8.314 g/L, Tricine 4mM, L-cysteine 0.1mM.

Preferably, in step (2), the electrostatic adsorption process is as follows: dispersing the CdS-bacterial precursor in pure water to obtain a dispersion, then adding GO solution to the dispersion, first adsorption, solid-liquid separation , to obtain CdS-bacteria/GO hybrid, then disperse the CdS-bacteria/GO hybrid in NiCl ₂ solution, adsorb for the second time, and separate solid-liquid to obtain CdS-bacteria/GO/Ni composite precursor.

Further preferably, the concentration of CdS-bacterial precursor in the dispersion liquid is OD600=1.5-2.5.

Further preferably, the concentration of GO in the GO solution is 0.3-0.5 mg/mL, and the volume ratio of the GO solution to the dispersion liquid is 1:3-6.

Further preferably, the time of the first adsorption is 30-100 min.

In the actual operation process, the first adsorption process and the second adsorption process are carried out under magnetic stirring. After the adsorption is completed, the desired product is obtained by centrifugal separation. The speed and time of centrifugal separation can be set according to conventional techniques, such as centrifugation at 8,000 rpm for 5 min.

Further preferably, in the NiCl ₂ solution, the concentration of NiCl ₂ is 3-6 g/L.

Further preferably, the solid-liquid mass volume ratio of the CdS-bacteria/GO hybrid to the NiCl ₂ solution is 1-3g: 100mL

Further preferably, the time of the second adsorption is 2-6h, preferably 4h.

Preferably, the CdS-bacteria/GO/Ni composite precursor obtained in step (2) is vacuum freeze-dried to constant weight and then pyrolyzed.

Preferably, in step (3), the temperature of the pyrolysis treatment is 600-800°C, the time of the pyrolysis treatment is 1-3h, and the heating rate is 2-5°C/min.

Further preferably, the temperature of the high-temperature pyrolysis treatment is 700°C, the heating rate is 5°C/min, and the holding time is 2h.

Preferably, in step (3), the protective atmosphere is a nitrogen atmosphere.

In the pyrolysis reaction of the present invention, insufficient pyrolysis temperature, too short time and too slow heating rate will lead to insufficient in-situ vulcanization of the sample; too high pyrolysis temperature, too long time and too fast heating rate will cause sulfur Source loss, product morphology change, and too thick graphene matrix. And carry out pyrolysis with the above-mentioned conditions of the present invention, have better in-situ vulcanization effect, and the obtained product has better OER performance.

The present invention also provides the application of the above-mentioned Ni/Ni ₃ S ₂ nano-cluster-graphene composite material, and the Ni/Ni ₃ S ₂ nano-cluster-graphene composite material is used as an OER catalytic electrode material.

Principles and Advantages

1. The present invention utilizes the method mediated by bacterial deposition to realize the in _- situ sulfide of Ni ²⁺ by using nano _- sized CdS as the sulfur source during the pyrolysis process. The coupled composite nanoclusters are anchored on the graphene, forming a Ni/ _Ni3S2 nanocluster composite structure uniformly distributed _on the graphene matrix. Uniform distribution and size control of the nanoclusters are guaranteed through controllable in-situ sulfidation and reduction. In addition, there is a strong coupling between Ni ₃ S ₂ and elemental Ni, forming crystal defects and increasing active sites. Due to the difference in electronegativity, the electrons on the metallic Ni are shifted to _S , resulting in S in an electron _- rich state, which further optimizes the catalytic activity of Ni3S2, and at the same time promotes the transfer of electrons from the surface active sites to the metallic Ni during the reaction process. The good conductivity of Ni facilitates the further conduction of electrons to the graphene conductive substrate, thereby forming a high-conductivity framework to ensure electron transfer during the catalytic process and improve catalytic performance.

2. The present invention regulates the degree of the in-situ sulfidation reaction by adjusting the pyrolysis temperature and time. During the pyrolysis process, Cd ²⁺ is reduced to Cd elemental substance and forms Cd steam overflow, which optimizes the pore structure and increases the specific surface area. , thereby promoting the mass transfer of the catalytic process.

3. The electrode of the Ni/Ni ₃ S ₂ nanocluster-graphene composite material provided by the present invention exhibits excellent catalytic activity in the OER reaction. It can be seen from the electrochemical test results that the Ni/Ni ₃ S ₂ nanocluster- When the graphene composite electrode undergoes OER reaction under alkaline conditions, a large current density of 100 mAcm ^-2 can be achieved with only 320 mV, and the Tafel slope is also as low as 41 mVdec ^-1 , confirming its high intrinsic reactivity. The decay-continuous electro-desorption of oxygen also proves that the Ni/Ni ₃ S ₂ nanocluster-graphene composite has good catalytic stability and applicability.

Description of drawings

1 is a transmission electron microscope (TEM) image of the Ni/Ni ₃ S ₂ nanocluster-graphene composite material obtained in Example 1 of the present invention.

2 is an X-ray diffraction (XRD) pattern of the Ni/Ni ₃ S ₂ nanocluster-graphene composite materials obtained in Example 1 and Comparative Example 1 of the present invention.

Fig. 3 is the electrochemical performance characterization diagram of the OER reaction of Ni/Ni ₃ S ₂ nanocluster-graphene composite material obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention in 1MKOH solution;

Among them, (a) is the comparison of the polarization curves of the OER reaction of different composite materials; (b) is the comparison of the Tafel slopes of the OER reaction of different composite materials.

Fig. 4 is the stability test curve of the continuous electrolysis of the electrode of the Ni/Ni ₃ S ₂ nanocluster-graphene composite material obtained in Example 1 of the present invention in 1MKOH solution.

Detailed ways

The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited thereto.

Unless otherwise specified, the starting materials and reagents used in the following examples are either commercially available or can be prepared by known methods.

Example 1

The present embodiment 1 provides a preparation method of a graphene-supported Ni/Ni ₃ S ₂ nanocluster composite material, which comprises the following steps:

(1) Inoculate the Pandoraea sp.B-6 cells preserved on the LB slope in the LB liquid medium, and at a temperature of 30° C., cultivate for 18 h to obtain the seed liquid of Pandoraea sp.B-6; wherein the LB liquid The ratio of each component of the medium is: peptone 10g, yeast powder 5g, sodium chloride 10g, distilled water 1L; the LB slant is based on the above formula by adding 15g/L agar;

(2) the Pandoraea sp.B-6 seed liquid obtained was centrifuged for 5 minutes under 8000rpm conditions, discarded supernatant, collected thalline;

(3) The collected Pandoraea sp.B-6 cells were inoculated into a Cd-containing sterile medium at a temperature of 30° C. according to 10% of the inoculation amount (the ratio of the volume of the transferred bacterial solution and the volume of the culture solution after inoculation). , natural pH, cultured for 24h, and centrifuged at 8,000rpm for 5min to obtain bacterial cells; wherein the composition ratio of the Cd-containing sterile medium is: glucose 2g/L, Cd(NO ₃ ) ₂ , 0.4mM, NH ₄ Cl 1.5 g/L, MgCl ₂ 0.2 g/L, CaCl ₂ 0.01 g/L, FeSO ₄ ·7H ₂ O 0.015 g/L, MnSO ₄ ·H ₂ O 0.01 g/L; MOPs 8.314 g/L, trineg /L, L-cysteine 0.1mM.

(4) Disperse the CdS-bacterial precursor obtained in the previous step in 200 mL of pure water to adjust the concentration to OD600=2, add 50 mL of GO solution with a concentration of 0.5 mg/mL, and stir magnetically for 30 min. Centrifugation was performed at 8,000 rpm for 5 min to obtain the CdS-bacteria/GO hybrid.

(5) Disperse the obtained CdS-bacteria/GO hybrid in 100 mL of a NiCl solution with a concentration of ₅ g/L at a solid-liquid ratio of 2% (2 g) for 4 h, and centrifuge at 8,000 rpm for 5 min to obtain CdS-bacteria/ GO/Ni composite precursor.

(6) vacuum freeze-drying the obtained CdS-bacteria/GO/Ni composite precursor to a constant weight, and then perform a pyrolysis reaction under an inert atmosphere to obtain a graphene-supported Ni/Ni ₃ S ₂ nanocluster composite material. The atmosphere of solution treatment is nitrogen atmosphere, the temperature is 700℃, the time of carbonization treatment is 2h, and the heating rate is 5℃/min;

The TEM results of the catalyst material prepared in Example 1 are shown in Figure 1, and the XRD pattern of the catalyst material prepared in Example 1 is shown in Figure 2. According to the corresponding crystal phase comparison results of XRD, it is shown that the composite material is graphite Graphene, a composite hybrid of metallic Ni and Ni ₃ S ₂ , it can be seen from the TEM image that the material structure is a graphene-supported nano-cluster of metallic Ni and Ni ₃ S ₂ coupled, and the size of the nano-cluster is between 10-100 nm. The diameter of the nanoclusters is about 30 nm and the distribution is uniform.

The catalytic material and Nafion were dispersed in a mixed solvent of ethanol and pure water, mixed uniformly by ultrasonic, and then dropped onto a glassy carbon electrode (0.4 cm in diameter) for natural drying to make a working electrode. On the electrode, the Hg/HgO electrode was used as the reference electrode, and the 1M KOH aqueous solution was used as the electrolyte), and its electrochemical performance was tested.

Figure 3(a) is the polarization curve of the electrode prepared in Example 1 and the comparative example at a scan rate of 5 mV/s, and Figure 3(b) is the Tafel curve of the electrode prepared in Example 1 and the comparative example. It can be seen that the synthesis is mediated by biodeposition. The graphene-supported Ni/Ni ₃ S ₂ nanocluster composites showed a significant improvement in OER catalytic activity compared to the non-biologically active graphene/Ni composites and the non-Ni supported graphene/bacteria composites. The overpotential is only 320mV at a large current density of 100mAcm ^-2 , which is superior to most of the current advanced transition metal OER catalysts. This indicates that our prepared catalysts benefit from the excellent catalytic activity of ultra-small _- sized Ni/ _Ni3S2 nanoclusters as catalytically active units. Due to the importance of the active area, the evaluation of oxygen evolution catalysts was performed by calculating the electrochemically active surface area (ECSA). Apparently, compared with the reported _Ni2S3 catalysts, the catalyst synthesized in this example has a dominant electrochemically active surface area of 15.6 mF cm ^-2 _. Meanwhile, the Tafel slope of this material is 41mV dec ^-1 , which is much lower than that of the comparative example, indicating a stronger mass/charge transfer capability. The promoted OER kinetics are attributed to the improved electron transport and the increased number of active surface sites on the in situ generated nanointerfaces.

To examine the OER stability of the catalysts, we continuously run the OER at a constant current of 100 mA cm ^-2 for 30 h (Fig. 4). During this period, the overpotentials of the catalysts synthesized in this example can be kept stable without obvious fluctuations. The results show that the graphene-supported Ni/Ni ₃ S ₂ nanocluster composites have good cycling stability.

In summary, the in-situ self-growth structure and interfacial coupling effect of the graphene-supported Ni/Ni ₃ S ₂ nanocluster composites of the present invention endow them with abundant OER catalytic active sites and excellent catalytic stability, which can be used in Efficient and stable catalysis of OER at low overpotentials during electrochemical reactions has promising application prospects.

Example 2

(1) The seed liquid of Pandoraea sp.B-6 was obtained by culturing according to steps (1) and (2) in Example 1.

(2) the Pandoraea sp.B-6 seed liquid obtained was centrifuged for 5 minutes under 8000rpm conditions, discarded supernatant, collected thalline;

(3) The collected Pandoraea sp.B-6 cells were inoculated into a Cd-containing sterile medium at a temperature of 30° C. according to 10% of the inoculation amount (the ratio of the volume of the transferred bacterial solution and the volume of the culture solution after inoculation). , natural pH, cultured for 18h, and centrifuged at 8,000rpm for 5min to obtain bacterial cells; wherein the composition ratio of the Cd-containing sterile medium is: glucose 2g/L, Cd(NO ₃ ) ₂ , 0.3mM, NH ₄ Cl 1.5 g/L, MgCl ₂ 0.2 g/L, CaCl ₂ 0.01 g/L, FeSO ₄ ·7H ₂ O 0.015 g/L, MnSO ₄ ·H ₂ O 0.01 g/L; MOPs 8.314 g/L, trineg /L, L-cysteine 0.1mM.

(4) Disperse the CdS-bacterial precursor obtained in the previous step in 200 mL of pure water to adjust the concentration to OD600=2, add 50 mL of GO solution with a concentration of 0.5 mg/mL, and stir magnetically for 30 min. Centrifugation was performed at 8,000 rpm for 5 min to obtain the CdS-bacteria/GO hybrid.

(5) The obtained CdS-bacteria/GO hybrid was dispersed in 100 mL of NiCl ₂ solution with a concentration of 5 g/L under magnetic stirring for 4 h, and centrifuged at 8,000 rpm for 5 min to obtain the CdS-bacteria/GO/Ni composite precursor.

(6) vacuum freeze-drying the obtained CdS-bacteria/GO/Ni composite precursor to a constant weight, and then perform a pyrolysis reaction under an inert atmosphere to obtain a graphene-supported Ni/Ni ₃ S ₂ nanocluster composite material. The atmosphere of the solution treatment is a nitrogen atmosphere, the temperature is 800 °C, the carbonization treatment time is 3 h, and the heating rate is 5 °C/min;

The electrochemical properties were tested by the same method as in Example 1.

The catalyst material prepared in Example 2 has an overpotential of 350mV at 100mAcm ^-2 and a Tafel slope of 54mVDec ^-1 under the condition of a scan rate of 5mV/s, showing excellent OER catalytic activity and fast reaction dynamics.

Example 3

(1) The seed liquid of Pandoraea sp.B-6 was obtained by culturing according to steps (1) and (2) in Example 1.

(2) the Pandoraea sp.B-6 seed liquid obtained was centrifuged for 5 minutes under 8000rpm conditions, discarded supernatant, collected thalline;

(3) The collected Pandoraea sp.B-6 cells were inoculated into a Cd-containing sterile medium at a temperature of 30° C. according to 10% of the inoculation amount (the ratio of the volume of the transferred bacterial solution and the volume of the culture solution after inoculation). , natural pH, cultured for 18h, and centrifuged at 8,000rpm for 5min to obtain bacterial cells; wherein the composition ratio of the Cd-containing sterile medium is: glucose 2g/L, Cd(NO ₃ ) ₂ , 0.4mM, NH ₄ Cl 1.5 g/L, MgCl ₂ 0.2 g/L, CaCl ₂ 0.01 g/L, FeSO ₄ ·7H ₂ O 0.015 g/L, MnSO ₄ ·H ₂ O 0.01 g/L; MOPs 8.314 g/L, trineg /L, L-cysteine 0.1mM.

(4) Disperse the CdS-bacterial precursor obtained in the previous step in 200 mL of pure water to adjust the concentration to OD600=2, add 50 mL of GO solution with a concentration of 0.5 mg/mL, and stir magnetically for 30 min. Centrifugation was performed at 8,000 rpm for 5 min to obtain the CdS-bacteria/GO hybrid.

(5) The obtained CdS-bacteria/GO hybrid was dispersed in 100 mL of NiCl ₂ solution with a concentration of 5 g/L under magnetic stirring for 4 h, and centrifuged at 8,000 rpm for 5 min to obtain the CdS-bacteria/GO/Ni composite precursor.

(6) vacuum freeze-drying the obtained CdS-bacteria/GO/Ni composite precursor to a constant weight, and then perform a pyrolysis reaction under an inert atmosphere to obtain a graphene-supported Ni/Ni ₃ S ₂ nanocluster composite material. The atmosphere of solution treatment is nitrogen atmosphere, the temperature is 600℃, the time of carbonization treatment is 2h, and the heating rate is 3℃/min;

The electrochemical properties were tested by the same method as in Example 1.

The catalyst material prepared in Example 3 has an overpotential of 335mV at 100mA cm ^-2 and a Tafel slope of 47mV Dec ^-1 under the condition of a scan rate of 5mV/s.

Comparative Example 1

The preparation method of the graphene/Ni composite material involved in this comparative example adopts simple electrostatic adsorption synthesis, does not involve biological action under this condition, and concrete steps are as follows:

(1) 50 mL of GO solution with a concentration of 0.5 mg/mL was added dropwise to 100 mL of a NiCl ₂ solution with a concentration of 5 g/L under magnetic stirring for 4 h and centrifuged at 8,000 rpm for 5 min to obtain a GO/Ni hybrid.

(2) vacuum freeze-drying the obtained GO/Ni hybrid to a constant weight, and then perform a pyrolysis reaction under an inert atmosphere to obtain a graphene/Ni composite material. The atmosphere of the pyrolysis treatment is a nitrogen atmosphere, and the temperature is 700° C., The carbonization treatment time was 2h, and the heating rate was 5°C/min;

Figure 1(b) is the TEM image of the graphene/Ni composite prepared in Comparative Example 1. It can be seen that Ni nanoparticles cannot be observed in the structure of stacked graphite sheets, indicating that the absence of bacteria-mediated electrostatic adsorption cannot prevent graphite Aggregation and accumulation of lamellae.

The electrochemical properties were tested by the same method as in Example 1.

The overpotential is 470 mV at a current density of 20 mAcm ⁻² , which is much higher than that of the example (˜250 mV), and the Tafel slope is 207 mV dec ⁻¹ , indicating a poor mass/charge transfer process. The results indicate that the structure and electrocatalytic activity of the composite hybrids can be significantly optimized by bio-mediated in situ sulfidation and self-grown Ni/Ni ₃ S ₂ nanoclusters.

Comparative Example 2

The preparation method of the graphene/CdS composite material involved in this comparative example adopts the same steps as the embodiment, but does not involve the adsorption of Ni ²⁺ under this condition, and the specific steps are as follows:

(1) Prepare the CdS-bacteria/GO precursor according to steps (1), (2), (3) and (4) in Example 1.

(2) after the obtained CdS/GO precursor is freeze-dried to constant weight by vacuum freeze-drying, a pyrolysis reaction is carried out under an inert atmosphere to obtain a graphene/CdS composite material, and the atmosphere of the pyrolysis treatment is a nitrogen atmosphere, and the temperature is 700° C., The carbonization treatment time was 2h, and the heating rate was 5°C/min;

The atomic ratio of C/Cd/S in the graphene/CdS composite prepared in this comparative example 2 is 76.85/11.52/11.63, indicating that the CdS/GO hybrid cannot be reduced by pyrolysis without Ni ²⁺ And removal of Cd ²⁺ , the remaining CdS nanoparticles do not have OER catalytic activity. This result indicates that Ni ²⁺ catalyzes the reduction of Cd ²⁺ during pyrolysis to form elemental Cd vapor release, while Ni reacts with the retained S source to achieve in-situ sulfide and self-growth to form Ni/Ni ₃ S ₂ nanoclusters as Efficient catalytically active centers anchored on graphene.

Comparative Example 3

(1) The seed liquid of Pandoraea sp.B-6 was obtained by culturing according to steps (1) and (2) in Example 1.

(2) the Pandoraea sp.B-6 seed liquid obtained was centrifuged for 5 minutes under 8000rpm conditions, discarded supernatant, collected thalline;

(3) The collected Pandoraea sp.B-6 cells were inoculated into a Cd-containing sterile medium at a temperature of 30° C. according to 10% of the inoculation amount (the ratio of the volume of the transferred bacterial solution and the volume of the culture solution after inoculation). , natural pH, cultured for 18h, and centrifuged at 8,000rpm for 5min to obtain bacterial cells; wherein the composition ratio of the Cd-containing sterile medium is: glucose 2g/L, Cd(NO ₃ ) ₂ , 0.4mM, NH ₄ Cl 1.5 g/L, MgCl ₂ 0.2 g/L, CaCl ₂ 0.01 g/L, FeSO ₄ ·7H ₂ O 0.015 g/L, MnSO ₄ ·H ₂ O 0.01 g/L; MOPs 8.314 g/L, trineg /L, L-cysteine 0.1mM.

(4) Disperse the CdS-bacterial precursor obtained in the previous step in 200 mL of pure water to adjust the concentration to OD600=2, add 50 mL of GO solution with a concentration of 0.5 mg/mL, and stir magnetically for 30 min. Centrifugation was performed at 8,000 rpm for 5 min to obtain the CdS-bacteria/GO hybrid.

(5) The obtained CdS-bacteria/GO hybrid was dispersed in 100 mL of NiCl ₂ solution with a concentration of 5 g/L under magnetic stirring for 4 h, and centrifuged at 8,000 rpm for 5 min to obtain the CdS-bacteria/GO/Ni composite precursor.

(6) vacuum freeze-drying the obtained CdS-bacteria/GO/Ni composite precursor to a constant weight, and then perform a pyrolysis reaction under an inert atmosphere to obtain a graphene-supported Ni/Ni ₃ S ₂ nanocluster composite material. The atmosphere of the solution treatment is nitrogen atmosphere, the temperature is 900°C, the carbonization treatment time is 2h, and the heating rate is 5°C/min;

The electrochemical properties were tested by the same method as in Example 1.

The catalyst material prepared by the comparative example 3 has an overpotential of 450 mV at 100 mA cm ^-2 and a Tafel slope of 76 mV dec ^-1 under the condition of a scan rate of 5 mV/s. The pyrolysis temperature has a significant impact on the catalyst structure. Too high pyrolysis temperature will trigger the catalytic graphitization reaction of Ni, resulting in the formation of a thicker graphite shell, which will hinder the accessibility of active sites and thus affect the catalytic activity. It can be seen that the pyrolysis temperature plays a crucial role in the formation of the graphene _- supported Ni/ _Ni3S2 nanocluster composite structure.

Claims (10)

1. Ni/Ni₃S₂The nano-cluster-graphene composite material is characterized in that: the composite material is prepared by uniformly fixing a graphene matrix onNi/Ni on graphene substrate₃S₂And (4) nano-cluster composition.

2. Ni/Ni alloy according to claim 1₃S₂The nano-cluster-graphene composite material is characterized in that: the Ni/Ni₃S₂The diameter of the nano-cluster is 10 nm-100 nm.

3. A Ni/Ni alloy according to claim 1 or 2₃S₂The preparation method of the nano-cluster-graphene composite material is characterized by comprising the following steps:

(1) inoculating bacteria into a Cd-containing sterile culture medium, culturing, and performing solid-liquid separation to obtain a CdS-bacteria precursor;

(2) sequentially loading graphene oxide and Ni on the CdS-bacterial precursor obtained in the step (1) through electrostatic adsorption²⁺Carrying out solid-liquid separation and drying to obtain a sandwich CdS-bacterium/GO/Ni composite precursor;

(3) putting the CdS-bacterium/GO/Ni composite precursor obtained in the step (2) into a protective atmosphere for pyrolysis treatment, wherein the obtained pyrolysis product is Ni/Ni₃S₂A nanocluster-graphene composite material.

4. Ni/Ni alloy according to claim 3₃S₂The preparation method of the nano-cluster-graphene composite material is characterized by comprising the following steps: the bacteria are Pandora sp.B-6 with the preservation number of CGMCC No. 4239.

5. Ni/Ni alloy according to claim 3₃S₂The preparation method of the nano-cluster-graphene composite material is characterized by comprising the following steps: in the step (1), the culture condition of the bacteria is that the inoculum size is 2-10%, the temperature is 25-40 ℃, the natural pH condition is adopted, and the culture time is 20-36 h;

in the step (1), Cd in the Cd-containing sterile culture medium²⁺The molar concentration of (B) is 0.2-0.5 mM.

6. Ni/Ni alloy according to claim 3₃S₂The preparation method of the nano-cluster-graphene composite material is characterized by comprising the following steps: the sterile culture medium containing Cd is a sterile culture medium taking glucose as a unique carbon source, and the components of the sterile culture medium are 2g/L of glucose and Cd (NO)₃)₂ 0.2-0.5mM，NH₄Cl1.5 g/L，MgCl₂ 0.2g/L，CaCl₂0.01g/L，FeSO₄·7H₂O 0.015g/L，MnSO₄·H₂O 0.01g/L；MOPs8.314g/L，Tricine 4mM，L-cysteine 0.1mM。

7. Ni/Ni alloy according to claim 3₃S₂The preparation method of the nano-cluster-graphene composite material is characterized by comprising the following steps: in the step (2), the electrostatic adsorption process comprises: dispersing CdS-bacteria precursor in pure water to obtain dispersion, adding GO solution into the dispersion, performing first adsorption and solid-liquid separation to obtain CdS-bacteria/GO hybrid, and dispersing the CdS-bacteria/GO hybrid in NiCl₂And (3) in the solution, performing second adsorption and solid-liquid separation to obtain the CdS-bacterium/GO/Ni composite precursor.

8. Ni/Ni alloy according to claim 7₃S₂The preparation method of the nano-cluster-graphene composite material is characterized by comprising the following steps: the concentration of the CdS-bacterial precursor in the dispersion liquid is 1.5-2.5 relative to OD 600;

the concentration of GO in the GO solution is 0.3-0.5mg/mL, and the volume ratio of the GO solution to the dispersion liquid is 1: 4;

the NiCl₂In solution, NiCl₂The concentration of (A) is 3-6 g/L;

the CdS-bacterium/GO hybrid with NiCl₂The solid-liquid mass volume ratio of the solution is 1-3 g: 100 mL.

9. Ni/Ni alloy according to claim 3₃S₂The preparation method of the nano-cluster-graphene composite material is characterized by comprising the following steps: in the step (3), the temperature of the pyrolysis treatment is 600-.

10. A Ni/Ni alloy according to claim 1 or 2₃S₂Application of nano-cluster-graphene composite material, and application of Ni/Ni₃S₂The nano-cluster-graphene composite material is used as an OER catalytic electrode material.

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