CN114990630A

CN114990630A - Preparation method and application of ZIF-67-derived hollow bimetal MOF/nitrogen-doped carbon composite material electrocatalyst

Info

Publication number: CN114990630A
Application number: CN202210579480.6A
Authority: CN
Inventors: 桑艳; 李国洪; 丁高飞; 郭子璇; 张若雪; 顾紫琼
Original assignee: Anhui Normal University
Current assignee: Anhui Normal University
Priority date: 2022-05-25
Filing date: 2022-05-25
Publication date: 2022-09-02
Anticipated expiration: 2042-05-25
Also published as: CN114990630B

Abstract

The invention discloses a preparation method and application of a ZIF-67-derived hollow bimetal MOF/nitrogen-doped carbon composite material electrocatalyst, wherein the preparation method comprises the following steps: obtaining CoM-ZIF-67 through the reaction of cobalt salt, metal salt and dimethyl imidazole; the CoM-ZIF-67 and tannic acid react to obtain CoM-ZIF-67-TA; calcining and carbonizing CoM-ZIF-67-TA in a protective atmosphere to obtain a target product; the composite material is in a three-dimensional regular dodecahedron configuration, has a hollow structure inside, has excellent OER and HER electrocatalytic properties, and has good application in electrolytic water.

Description

Preparation method and application of ZIF-67-derived hollow bimetal MOF/nitrogen-doped carbon composite material electrocatalyst

Technical Field

The invention belongs to the field of electrocatalytic materials, and particularly relates to a preparation method and application of a ZIF-67-derived hollow bimetallic MOF/nitrogen-doped carbon composite electrocatalyst.

Background

With the continuous development of scientific society, fossil energy is continuously consumed in the world, and the ecological environment problem caused in the consumption process is more serious, so people begin to continuously develop sustainable and renewable energy sources to replace fossil fuels. Hydrogen energy is such a sustainable and renewable energy source. Electrocatalytic total hydrolysis is one of the effective sustainable routes to produce hydrogen energy, a green clean energy source, and includes two half-electrode reactions: hydrogen Evolution (HER) and Oxygen Evolution (OER) reactions, both of which are slow in kinetics, especially OER is a four electron transfer process, so efficient electrocatalysts are required to reduce the extra energy loss caused by multi-electron reactions.

RuO ₂ And Pt are well-known electrocatalysts excellent in oxygen evolution reaction and hydrogen evolution reaction, but their large-scale commercial applications are limited due to their high cost and scarcity. Therefore, the development of non-noble metal electrocatalysts with high efficiency and wide application range is a hot point of attention in the scientific research community at present.

Disclosure of Invention

The invention aims to provide a preparation method and application of a ZIF-67-derived hollow bimetallic MOF/nitrogen-doped carbon composite material electrocatalyst.

In order to realize the purpose, the technical scheme adopted by the invention is as follows:

the preparation method of the ZIF-67-derived hollow bimetallic MOF/nitrogen-doped carbon composite material electrocatalyst comprises the following steps of:

(1) dissolving cobalt salt and other metal salts except the cobalt salt in an alcohol solvent, adding the alcohol solution of dimethyl imidazole into the alcohol solvent under the condition of stirring, uniformly mixing the two, standing for growth, washing and drying to obtain a bimetallic organic framework material CoM-ZIF-67;

(2) dissolving a bimetal organic framework material CoM-ZIF-67 in an alcohol solvent, adding a tannic acid solution under the stirring condition, continuously stirring for a certain time after the completion of the addition, and then washing and drying to obtain a hollow bimetal organic framework material CoM-ZIF-67-TA;

(3) the hollow bimetallic organic framework material CoM-ZIF-67-TA is calcined and carbonized in inert atmosphere to obtain the ZIF-67 derived hollow bimetallic MOF/nitrogen-doped carbon composite material electrocatalyst.

In the step (1), the molar ratio of the cobalt salt, the metal salt except the cobalt salt and the dimethyl imidazole is 1 (1-100) to (1-100), preferably 1: 1-5: 5-40, more preferably 1: 1: 32.

in the step (1), the concentration of the cobalt salt in the alcohol solvent is 0.01-0.2M, preferably 0.05-0.1M; the concentration of the dimethyl imidazole in the alcoholic solution is 0.1-1.0M, preferably 0.2-0.5M.

In the step (1), the standing growth condition is that the standing growth is carried out for 1-24 h at 10-60 ℃, preferably for 18-24 h at 20-35 ℃, and more preferably for 24h at 25 ℃.

In the step (1), the cobalt salt is selected from any one or two of cobalt nitrate and cobalt chloride; the metal salt other than cobalt salt is selected from any one of nickel salt, magnesium salt and zinc salt.

The nickel salt is selected from any one or two of nickel nitrate and nickel chloride.

The magnesium salt is selected from one or two of magnesium nitrate and magnesium chloride.

The zinc salt is selected from any one or two of zinc nitrate and zinc chloride.

The alcohol solvent is selected from any one or two of methanol and ethanol.

In the step (2), the mass ratio of the CoM-ZIF-67 to the tannin is 1: (0.1 to 10), preferably 1:1 to 5, more preferably 1: 2.5.

in the step (2), the tannic acid solution is a tannic acid aqueous solution, and the concentration of the tannic acid aqueous solution is 1-10 g/L, preferably 4-7 g/L; the concentration of the CoM-ZIF-67 in the alcohol solvent is 0.01-0.1 g/mL, preferably 0.05 g/mL.

In the step (2), the continuous stirring is performed under the condition of stirring at 10-60 ℃ for 1-60 min, preferably at 20-35 ℃ for 5-15 min, and more preferably at 25 ℃ for 10 min.

In the step (3), the inert atmosphere is argon or nitrogen; the calcination carbonization condition is that the temperature is raised to 300-900 ℃ at the temperature raising rate of 1-10 ℃/min and is kept for 1-8 h, the temperature is raised to 450-580 ℃ at the temperature raising rate of 1-5 ℃/min and is kept for 1.5-3 h, and the temperature is raised to 500 ℃ at the temperature raising rate of 2 ℃/min and is kept for 2 h.

The invention also provides the ZIF-67-derived hollow bimetallic MOF/nitrogen-doped carbon composite material-based electrocatalyst prepared by the preparation method, which is a hollow dodecahedral framework structure.

The invention also provides an application of the ZIF-67-derived hollow bimetallic MOF/nitrogen-doped carbon composite material electrocatalyst as a catalyst for HER or OER reaction.

The hollow bimetallic MOF/nitrogen-doped carbon composite material electrocatalyst derived based on ZIF-67 is prepared by firstly introducing second-phase metal into ZIF-67, etching the second-phase metal in a tannic acid solution to form a hollow dodecahedron framework structure, and finally carbonizing the dodecahedron framework structure in an inert atmosphere. According to the invention, ZIF-67 is used as a precursor, a framework structure is provided in subsequent calcination, a nitrogen source, a carbon source and a cobalt source are provided for the material, and the addition of the second-phase metal and the heterostructure of the nitrogen-doped carbon material are in a synergistic effect and complementary, so that the activation energy of the full hydrolysis reaction can be better reduced.

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

the preparation method of the ZIF-67-derived hollow bimetallic MOF/nitrogen-doped carbon composite material electrocatalyst is simple, the morphology of the electrocatalyst is a hollow dodecahedron framework structure, the electrocatalyst has a large specific surface area, more active sites can be provided for the catalyst to participate in HER or OER reaction, and the electrocatalyst has excellent electrochemical catalytic activity on both OER and HER.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) photograph at 10000 times magnification of a pale purple solid CoNi-ZIF-67 prepared in step (1) of example 1;

FIG. 2 is a Transmission Electron Microscope (TEM) image at 15000 times magnification of CoNi-ZIF-67-TA as a light brown solid prepared in step (2) of example 1;

FIG. 3 is a Scanning Electron Microscope (SEM) image at 80000 times magnification of the cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 1;

FIG. 4 is a Scanning Electron Microscope (SEM) image magnified 20000 times of the cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 1;

FIG. 5 is a 15000 Transmission Electron Microscope (TEM) magnified view of the hollow bimetallic organic framework/nitrogen-doped carbon composite prepared in example 1;

FIG. 6 is a 50000 Transmission Electron Microscope (TEM) magnification of a cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 1;

FIG. 7 is an XRD pattern of a cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 1;

FIG. 8 is a Scanning Electron Microscope (SEM) image at 35000 magnification of the cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 2;

FIG. 9 is a Scanning Electron Microscope (SEM) image at 90000 times magnification of a cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 2;

FIG. 10 is an SEM image of a cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 3;

FIG. 11 is a 30000 times magnified Scanning Electron Microscope (SEM) image of the cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 4;

fig. 12 is a 70000 times magnified Scanning Electron Microscope (SEM) image of the cobalt-magnesium hollow bimetallic organic framework/nitrogen-doped carbon composite prepared in example 5;

FIG. 13 is a Transmission Electron Microscope (TEM) image of a cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite prepared in example 6;

FIG. 14 is a graph showing the performance of oxygen evolution reactions obtained by electrochemical testing of cobalt-nickel hollow bimetallic organic framework/N-doped carbon composite materials prepared in examples 1-3 and the N-doped carbon material prepared in comparative example 1;

fig. 15 is a graph showing hydrogen evolution reaction performance test results obtained by performing an electrochemical test on the cobalt-nickel hollow bimetal organic framework/nitrogen-doped carbon composite material prepared in examples 1 to 3 and the nitrogen-doped carbon material prepared in comparative example 1.

Detailed Description

The present invention will be described in detail with reference to the following examples and drawings.

Example 1

A preparation method of a cobalt-nickel hollow bimetal organic frame/nitrogen-doped carbon composite material comprises the following steps:

(1) weighing 0.465g of cobalt nitrate hexahydrate and 0.465g of nickel nitrate hexahydrate, dissolving in 20mL of methanol to form a pink solution, and marking as a solution A; dissolving 4.200g of dimethylimidazole in 160mL of methanol to form a transparent solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 1 hour, standing for 24 hours, and finally centrifuging, washing and drying to obtain a light purple solid CoNi-ZIF-67, wherein the SEM picture of the solid is shown in figure 1;

(2) weighing 0.1g of CoNi-ZIF-67 prepared in the step (1), dissolving in 2mL of ethanol, and performing ultrasonic stirring to form a uniform mixed solution A; then 0.25g of tannic acid is weighed and evenly dispersed in 48mL of deionized water to form a light brown mixed solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 10min, and finally centrifuging, washing and drying to obtain a light brown solid CoNi-ZIF-67-TA, wherein an SEM picture of the light brown solid is shown in FIG. 2;

(3) and placing the prepared CoNi-ZIF-67-TA in a porcelain boat, placing the porcelain boat in a tubular furnace, adopting argon as protective gas, heating to 550 ℃ at the heating rate of 2 ℃/min, preserving the temperature for 2h, and naturally cooling to obtain a black solid nitrogen-doped carbon material, namely the final product, namely the cobalt-nickel hollow bimetal organic frame/nitrogen-doped carbon composite material.

The SEM and TEM are shown in figures 3-6, and it can be seen from the figures that the cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared by the embodiment retains the three-dimensional dodecahedron framework structure of the original ZIF-67, the size of the composite material is uniform, the particle size distribution is 250-300nm, and the interior of the composite material shows a hollow characteristic, and the morphology provides a large specific surface area for the material.

The XRD pattern is shown in FIG. 7.

Example 2

(1) weighing 0.465g of cobalt nitrate hexahydrate and 0.465g of nickel nitrate hexahydrate, dissolving in 20mL of methanol to form a pink solution, and marking as a solution A; dissolving 4.200g of dimethylimidazole in 160mL of methanol to form a transparent solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 1 hour, standing for 24 hours, and finally centrifuging, washing and drying to obtain a light purple solid CoNi-ZIF-67;

(2) weighing 0.1g of CoNi-ZIF-67 prepared in the step (1), dissolving in 2mL of ethanol, and performing ultrasonic stirring to form a uniform mixed solution A; then 0.25g of tannic acid is weighed and evenly dispersed in 48mL of deionized water to form a light brown mixed solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 10min, and finally centrifuging, washing and drying to obtain a light brown solid CoNi-ZIF-67-TA;

(3) and placing the prepared CoNi-ZIF-67-TA in a porcelain boat, placing the porcelain boat in a tubular furnace, adopting argon as protective gas, heating to 400 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 2h, and naturally cooling to obtain a black solid nitrogen-doped carbon material, namely the final product, namely the cobalt-nickel hollow bimetal organic frame/nitrogen-doped carbon composite material.

The SEM is shown in FIGS. 8-9, which shows that the cobalt-nickel hollow bimetal organic framework/nitrogen-doped carbon composite material with the original ZIF-67-retained three-dimensional dodecahedron framework structure is also prepared in the example, the size is uniform, the particle size is distributed at 250-300nm, but the temperature for calcination and carbonization is reduced relative to that of the example 1, the final carbonization inside the material is incomplete, and the catalytic performance of the material is influenced to a certain extent.

Example 3

(1) weighing 0.465g of cobalt nitrate hexahydrate and 0.465g of nickel nitrate hexahydrate, dissolving in 20mL of methanol to form a pink solution, and marking as a solution A; dissolving 4.200g of dimethyl imidazole in 160mL of methanol to form a transparent solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 1 hour, standing for 24 hours, and finally centrifuging, washing and drying to obtain a light purple solid CoNi-ZIF-67;

(3) and placing the prepared CoNi-ZIF-67-TA in a porcelain boat, placing the porcelain boat in a tubular furnace, adopting argon as protective gas, heating to 500 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 2h, and naturally cooling to obtain a black solid nitrogen-doped carbon material, namely the final product, namely the cobalt-nickel hollow bimetal organic frame/nitrogen-doped carbon composite material.

The SEM is shown in FIG. 10, and it can be seen from the figure that the cobalt-nickel hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in the embodiment retains the three-dimensional dodecahedral framework structure of the original ZIF-67, the size of the composite material is uniform, the particle size distribution is 250-300nm, and the interior of the composite material has a hollow characteristic, and the morphology provides a large specific surface area for the material.

Example 4

(3) and (3) placing the prepared CoNi-ZIF-67-TA into a porcelain boat, placing the porcelain boat into a tube furnace, heating to 600 ℃ at the heating rate of 2 ℃/min by using argon as protective gas, preserving the heat for 2 hours, and naturally cooling to obtain a black solid nitrogen-doped carbon material, namely the final product, namely the cobalt-nickel hollow bimetal organic frame/nitrogen-doped carbon composite material.

As shown in the SEM image of FIG. 11, since the temperature of calcination and carbonization was increased to 600 ℃ relative to that of example 1, the metal particles in the material were agglomerated, and the final product could not retain the three-dimensional dodecahedral framework structure of the original ZIF-67.

Example 5

(1) 0.620g of cobalt nitrate hexahydrate and 0.274g of magnesium nitrate hexahydrate are weighed and dissolved in 20mL of methanol to form a pink solution which is marked as solution A; dissolving 4.200g of dimethylimidazole in 160mL of methanol to form a transparent solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 1 hour, standing for 24 hours, and finally centrifuging, washing and drying to obtain a light purple solid CoMg-ZIF-67;

(2) weighing 0.1g of CoMg-ZIF-67 prepared in the step (1), dissolving in 2mL of ethanol, and carrying out ultrasonic stirring to form a uniform mixed solution A; then 0.25g of tannic acid is weighed and evenly dispersed in 48mL of deionized water to form a light brown mixed solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 10min, and finally centrifuging, washing and drying to obtain light brown solid CoMg-ZIF-67-TA;

(3) and (3) placing the prepared CoMg-ZIF-67-TA in a porcelain boat, placing the porcelain boat in a tubular furnace, taking argon as protective gas, heating to 550 ℃ at the heating rate of 2 ℃/min, preserving the temperature for 2h, and naturally cooling to obtain a black solid nitrogen-doped carbon material, namely the final product cobalt-magnesium hollow bimetal organic frame/nitrogen-doped carbon composite material, wherein an SEM picture of the composite material is shown in figure 12.

Example 6

(1) 0.621g of cobalt nitrate hexahydrate and 0.310g of nickel nitrate hexahydrate were weighed out and dissolved in 20mL of methanol to form a pink solution, noted as solution A, and 4.200g of dimethylimidazole was dissolved in 160mL of methanol to form a clear solution B. And slowly adding the solution B into the solution A while stirring, continuously stirring for 1 hour, standing for 24 hours, and finally washing and drying by centrifugation to obtain a light purple solid CoNi-ZIF-67.

(2) 0.2g of CoNi-ZIF-67 prepared in step (1) was weighed, dissolved in 4mL of ethanol, and subjected to ultrasonic stirring to form a uniform mixed solution A, and 0.50g of tannic acid was weighed and uniformly dispersed in 96mL of deionized water to form a light brown mixed solution B. The solution B was slowly added to the solution a while stirring, stirring was continued for 10min, and finally the dried single light brown solid CoNi-ZIF-67-TA was washed by centrifugation.

The SEM or TEM image is shown in FIG. 13, and it can be seen that the simultaneous increase of the molar ratio does not affect the morphology of the final product.

Comparative example 1

The preparation method of the nitrogen-doped carbon material CoNi-ZIF-67/NC comprises the following steps:

(1) weighing 0.465g of cobalt nitrate hexahydrate and 0.465g of nickel nitrate hexahydrate, dissolving in 20mL of methanol to form a pink solution, and marking as a solution A; dissolving 4.200g of dimethylimidazole in 160mL of methanol to form a transparent solution B; slowly adding the solution B into the solution A while stirring, continuously stirring for 1 hour, standing for 24 hours, and finally, centrifugally washing and drying to obtain a light purple solid CoNi-ZIF-67;

(2) the preparation method comprises the following steps of (1); and (3) placing the CoNi-ZIF-67 in a porcelain boat, placing in a tube furnace, heating to 600 ℃ at a heating rate of 2 ℃/min by using argon as a protective gas, preserving heat for 3h, and naturally cooling to obtain a black solid nitrogen-doped carbon material, namely the CoNi-ZIF-67/NC.

Application example 1

Application of hollow bimetallic organic framework/nitrogen-doped carbon composite material as Oxygen Evolution Reaction (OER) catalyst

7mg of the hollow bimetallic organic frame/nitrogen-doped carbon composite material prepared in examples 1 to 3 and CoNi-ZIF-67/NC prepared in comparative example 1, 2mg of acetylene black as a conductive agent and 1mg of polyvinylidene fluoride (PVDF) powder as a binder were added to agate mortar and ground, respectively, until a fine powder was obtained, and then 50mL of N-methyl-2-pyrrolidone (NMP) as a solvent was added to form a uniform mixture. Uniformly coating the obtained mixture on a clean Nickel Foil (NF) with the size of 1cm multiplied by 1cm to obtain a uniform thin layer, and taking the uniform thin layer as a working electrode, a platinum sheet electrode as a counter electrode, an Ag/AgCl electrode as a reference electrode and an electrolyte as a 1mol/L potassium hydroxide solution; linear Sweep Voltammetry (LSV) at 5 mV.s ^-1 And the polarization curve was obtained at 90% ohmic compensation. As shown in FIG. 14, the current density was 10mA cm ^-2 When the hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 1 is used as a working electrode, the overpotential of OER is 181mV, which shows that the material has excellent electrochemical catalytic activity on OER.

Application example 2

Application of hollow bimetallic organic framework/nitrogen-doped carbon composite material as Hydrogen Evolution Reaction (HER) catalyst

Prepared by the method of examples 1-3The hollow bimetallic organic frame/nitrogen-doped carbon composite material and CoNi-ZIF-67/NC prepared in the comparative example 1 are coated on a nickel foil as a working electrode according to the method in the application example 1, a carbon rod electrode is a counter electrode, an Ag/AgCl electrode is a reference electrode, and an electrolyte is a 1mol/L potassium hydroxide solution; linear Sweep Voltammetry (LSV) at 5 mV.s ^-1 And the polarization curve was obtained at 90% ohmic compensation. As shown in FIG. 15, the current density was 10mA cm ^-2 When the over potential of the OER serving as a working electrode of the hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 1 is 62mV, the material shows excellent electrochemical catalytic activity on HER, and the electrochemical catalytic activity on HER of the hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 1 is greater than the electrochemical catalytic activity on HER of the hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 3 is greater than the electrochemical catalytic activity on HER of the hollow bimetallic organic framework/nitrogen-doped carbon composite material prepared in example 2 is greater than the electrochemical catalytic activity on HER of the nitrogen-doped carbon material CoNi-ZIF-67/NC prepared in comparative example 1.

The above detailed description of a ZIF-67 derived hollow bimetallic MOF/nitrogen doped carbon composite electrocatalyst and its applications with reference to the examples are illustrative and not limiting, and several examples can be cited within the limits of the invention, thus changes and modifications that do not depart from the general concept of the invention are intended to be within the scope of the invention.

Claims

1. A preparation method of a ZIF-67 derived hollow bimetallic MOF/nitrogen doped carbon composite material electrocatalyst is characterized by comprising the following steps of:

(2) dissolving a bimetallic organic framework material CoM-ZIF-67 in an alcohol solvent, adding a tannic acid solution under the stirring condition, continuously stirring for a certain time after the completion of the addition, and washing and drying to obtain a hollow bimetallic organic framework material CoM-ZIF-67-TA;

(3) the hollow bimetal organic framework material CoM-ZIF-67-TA is calcined and carbonized in inert atmosphere to obtain the ZIF-67-derived hollow bimetal MOF/nitrogen-doped carbon composite material electrocatalyst.

2. The method according to claim 1, wherein in the step (1), the molar ratio of the cobalt salt, the metal salt other than the cobalt salt, and the dimethylimidazole is 1 (1-100) to (1-100).

3. The preparation method according to claim 1, wherein in the step (1), the standing growth condition is 10-60 ℃ for 1-24 h.

4. The preparation method according to claim 1 to 3, wherein in the step (1), the cobalt salt is selected from any one or two of cobalt nitrate and cobalt chloride; the metal salt other than cobalt salt is selected from any one of nickel salt, magnesium salt and zinc salt.

5. The preparation method according to claim 1, wherein the alcohol solvent is selected from any one or two of methanol and ethanol.

6. The preparation method according to claim 1, wherein in the step (2), the mass ratio of the CoM-ZIF-67 to the tannic acid is 1: (0.1-10).

7. The preparation method according to claim 1, wherein in the step (2), the continuous stirring is performed at 10 to 60 ℃ for 1 to 60 min.

8. The production method according to claim 1, wherein in the step (3), the inert atmosphere is argon or nitrogen; the calcination carbonization condition is that the temperature is raised to 300-900 ℃ at the temperature rise rate of 1-10 ℃/min and is kept for 1-8 h.

9. The ZIF-67 derived hollow bimetallic MOF/nitrogen doped carbon composite electrocatalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the ZIF-67 derived hollow bimetallic MOF/nitrogen doped carbon composite based electrocatalyst according to claim 9 as catalyst for HER or OER reactions.