EP-4735383-A1 - METHOD OF FORMING N-DOPED CARBON NANOFOAM

Abstract

The present disclosure relates to methods of forming an N-doped carbon nanofoam, which finds particular use as a fuel storage material. The N-doped carbon nanofoam is produced by introducing nitrogen to a carbon nanofoam, said nitrogen being introduced during or after formation of the carbon nanofoam. Many sources of nitrogen are useful including non-aqueous nitrogen sources. The method of the disclosure allows for large scale production of N-doped carbon nanofoams.

Inventors

• HEIM, Zacariah Austin

Assignees

• Prometheon Technologies BV

Dates

Publication Date

20260506

Application Date

20240628

Claims (16)

1. 1. A method of forming an N-doped carbon nanofoam comprising the steps of i. providing a mixture of sugar, water, and hydrocarbon mediator; ii. heating said mixture in the presence of a nitrogen source at 400°C to 800°C to form an N-doped carbon nanofoam; iii. optionally, pitting the formed N-doped carbon nanofoam.
2. 2. The method of claim 1, wherein the nitrogen source is added in step i.
3. 3. The method of claims 1 or 2, comprising the steps of: i. providing a mixture of sugar, water, hydrocarbon mediator and a nitrogen source; ii. heating said mixture at 400°C to 800°C to form an N-doped carbon nanofoam; iii. optionally, pitting the N-doped carbon nanofoam.
4. 4. The method of claim 1, wherein the mixture of sugar, water, and hydrocarbon mediator is heated prior to addition of a nitrogen source.
5. 5. The method of claim 4 comprising the steps of: i. providing a mixture of sugar, water, and hydrocarbon mediator; iia. heating said mixture at 100°C to 600°C to form a carbon nanofoam at least partially; iib. heating said at least partially formed carbon nanofoam in the presence of a nitrogen source at 400°C to 800°C to form an N-doped carbon nanofoam; iii. optionally, pitting the N-doped carbon nanofoam.
6. 6. The method of any of the preceding claims, wherein the nitrogen source is selected from the group consisting of ammonia; urea; melamine; proteins such as albumin or egg whites; polymers such as polyacrylonitrile, polyvinylpyridine; heteroaromatic compounds such as triazine, pyrimidine, pyridazine, pyrazine, pyridine, pyrrole, imidazole, pyrazole, and 1,2,4-triazole; coal tar pitch; and/or mixtures thereof.
7. 7. The method of any of the preceding claims, wherein the nitrogen source is decomposed thermally.
8. 8. The method of any of the preceding claims, wherein, the nitrogen source is decomposed mechanically.
9. 9. The method of any of the preceding claims, wherein the N content of the N-doped carbon nanofoam is from 0.1 to 15 wt%.
10. 10. The method of any of the preceding claims, wherein the mixture of sugar and water is at least 3 molar.
11. 11. The method of any of the preceding claims, wherein the weight ratio of hydrocarbon mediator to sugar is from 1 :25,000 to 1:75,000.
12. 12. The method of any of the preceding claims, wherein the hydrocarbon mediator is selected from the group consisting of pyrene, chrysene, benz[a]anthracene, fluoranthene, anthracene, naphthalene, benzene, hexane and/or mixtures thereof, with anthracene, naphthalene or benzene being preferred and naphthalene being most preferred.
13. 13. The method of any of the preceding claims, wherein suitable sugars include monosaccharides, disaccharides and trisaccharides.
14. 14. The method of any of the preceding claims, wherein suitable sugars include sucrose, glucose or fructose, with sucrose being preferred.
15. 15. The method of any of the preceding claims, wherein the N-doped carbon nanofoam undergoes pitting.
16. 16. An N-doped carbon nanofoam according to any of the methods of any of the preceding claims.

Description

METHOD OF FORMING N-DOPED CARBON NANOFOAM FIELD The present disclosure relates to a method of forming an N-doped carbon nanofoam. The N-doped carbon nanofoam of the disclosure is suitable for use as a conductive support scaffold for catalysts in fuel cells. BACKGROUND Carbon materials provide useful electrocatalysts due to their high surface area, high conductivity and cost. Various types of carbon materials suitable for use as electrocatalysts are disclosed in X. Wang et al., Adv. Energy Mater., 2017, 7, 1700544. Non-metal atoms such as N, P, S and B can be doped into the carbon structure, resulting in multiple possible configurations of doped carbon material. Being more electronegative than carbon, these heteroatoms make neighbouring carbon atoms electron deficient, thereby promoting oxygen adsorption on the carbon nanostructure. Doped carbon structures may take various forms, including nanotubes, sheets or particulate carbon materials. Of these doping atoms, N is advantageous as it provides a stable material having the desired balance of properties. Specifically, the N-doping provides faster electron transfer, decreased bulk resistance and increased coupling efficiency when the material is modified by a catalytic metal. In contrast, doping with S and P typically acidifies the carbon leading to a material with higher pH sensitivity. Modification with S typically leaves a carbon material having a highly reactive surface, which can lead to poorer lifetime and side reactions occurring. The present disclosure provides methods of making an N-doped carbon nanofoam material having excellent properties as a component in redox catalysts in fuel cells. A known method of forming an N-doped carbon nanofoam is to heat a combined mixture of mesoporous carbon source and an aqueous acidic nitrogen source. Aqueous acidic nitrogen sources, for example nitric acid or nitrous acid are relatively cheap and provide efficient N-doping. A drawback of using an aqueous acidic nitrogen source is that to provide high levels of N- doping, relatively high concentrations of the acid is required. In addition to N-doping, the harsh conditions can also cause pitting of the carbon nanofoam. Over-pitting or uncontrolled pitting results in loss of some of the mesoporous structure, which may decrease the surface area of the carbon nanofoam. In addition, an aqueous acidic nitrogen source also promotes the formation of carboxylate groups surface of the material during N-doping. When carboxylate groups are formed, the conductivity of the resultant doped nanofoam is reduced leading to an inferior material for use in electronic systems e.g., fuel cells. When using an aqueous acidic nitrogen source, the conditions therefore need to be carefully controlled in order to provide the desired amount of doping whilst simultaneously avoiding material degradation. In addition, methods comprising acidic nitrogen sources such as an aqueous acidic nitrogen source, pose serious health and safety risks when implemented on a large scale. This is not only impractical, but also expensive to manage and maintain when implemented on an industrial scale. Accordingly, there is a need for a safe method of producing N-doped carbon nanofoams that provide the desired level of N-doping, without uncontrolled degradation the carbon nanofoam superstructure. Whilst some of the problems associated using nitric acid may be solved by switching to a non-aqueous nitric acid source, the problems associated with over-pitting, material degradation and safety may still arise due to the harsh acid conditions. The method of the disclosure solves this problem by providing a method of forming an N- doped carbon nanofoam wherein the nitrogen source is, for example, a non-aqueous nitrogen source. SUMMARY The present disclosure relates to the method of forming an N-doped carbon nanofoam, which nanofoam finds particular use as a fuel storage material. Further, the disclosure relates to an N-doped carbon nanofoam formed by said method. According to a first aspect of the present disclosure is provided a method of forming an N- doped carbon nanofoam comprising the steps of: i. providing a mixture of sugar, water, and hydrocarbon mediator; ii. heating said mixture in the presence of a nitrogen source at 400°C to 800°C to form an N-doped carbon nanofoam; iii. optionally, pitting the N-doped carbon nanofoam. According to the present disclosure, there is provided a method of forming an N-doped carbon nanofoam comprising the steps of: i. providing a mixture of sugar, water, and hydrocarbon mediator; iia. heating said mixture at 100°C to 600°C to form a carbon nanofoam at least partially; iib. heating said at least partially formed carbon nanofoam in the presence of a nitrogen source at 400°C to 800°C to form an N-doped carbon nanofoam; iii. optionally, pitting the N-doped carbon nanofoam. According to the present disclosure, there is provided a method of forming an N-doped carbon nanofoam comprising