Carbon aerogels having high electric conductivity and adjustable microstructure for cathode design in metal-sulfur batteries and polymer-electrolyte membrane fuel cells

Abstract

The invention relates to carbon aerogels having high electric conductivity and adjustable microstructure in particular for cathode design in magnesium-sulfur batteries and polymer-electrolyte membrane fuel cells. The invention particularly refers to a high-conductivity carbon aerogel with adjustable microstructure, a method for its production and its use.

Description

[0001] Carbon aerosols with high electrical conductivity and tunable microstructure for cathode design in metal-sulfur batteries and polymer electrolyte membrane fuel cells

[0002] The invention relates to a highly conductive carbon aerogel with adjustable microstructure, a process for its production and its use.

[0003] The manufacturing process for carbon aerogels (CA) was first described by Richard Pekala in 1989. They are carbonized from organic aerogels, such as resorcinol-formaldehyde, melamine-formaldehyde, phenol-formaldehyde, etc. Due to their high surface area, pore volume, tunable porosity and pore size, and high electrical conductivity, carbon aerogels are excellent candidates for electrode materials. The open-pore network with tunable microstructure offers considerable freedom in material design, allowing the carbon matrix to be specifically tailored to the electrode's requirements.

[0004] CN 112811419A describes a carbon aerogel used in acoustics, optics, electrical engineering, dynamics, low-temperature thermal engineering, and the like. This aerogel has a high specific surface area, light weight, high porosity, good conductivity, and low thermal conductivity, and has wide applications in adsorption, energy conversion, storage, sensors, and thermal insulation materials. However, the preparation process of existing carbon aerogel is complex, and a sol-gel method or template-based method is generally used. The carbon aerogel preparation process includes the following steps: A. Uniformly mixing starch and deionized water at normal temperature, adding the mixed solution to deionized water at 100°C, and stirring uniformly until the entire mixture becomes semi-transparent;

[0005] B. aging the semi-transparent liquid obtained in step A at normal temperature, adding acetone as a substitute, adding dichloromethane as a substitute and carrying out a hydrophobic treatment;

[0006] C. Drying the liquid from step B to obtain a solid starch-carbon gel, introducing N2 into a tube furnace and gradually increasing the temperature to allow the starch aerogel to decompose and carbonize to obtain a carbon aerogel, and then cooling;

[0007] D. Continuous introduction of CO2 and heating and activation to obtain a black porous carbon aerogel.

[0008] The carbon aerogel comprises a multimodal pore size distribution with a structure formed by cross-linking a porous graphite layer. The carbon aerogel exhibits micropores, mesopores, and macropores.

[0009] DE 10 2013 216965 A1 relates to a process for producing organic RF aerogels. The process is characterized by the fact that gelation occurs in both basic and acidic conditions. This enables the production of nanostructured organic RF aerogels with drying under subcritical conditions. The described aerogels do not exhibit mesopores.

[0010] DE 10 2018 123285 (Al) relates to elastic carbon aerogels produced with defined amounts of substance. Only micropores are present. In particular, an electrode for a rechargeable battery is described, which comprises an active mass (AM) consisting of sulfur and a carbon matrix material in the form of an elastically deformable microporous carbon aerogel, in particular for use in a metal (e.g., lithium, magnesium, aluminum)-sulfur rechargeable battery, corresponding improved rechargeable batteries, a method for producing the electrode according to the invention, and the use of elastically deformable microporous carbon aerogels as matrix material for an electrode, in particular a sulfur electrode.

[0011] The rechargeable magnesium-sulfur (Mg-S) battery was first introduced by a research group at Toyota Motor Corp. in 2011. The virtually unlimited availability of sulfur and magnesium, high volumetric capacities of 3837 Ah / L, and high specific energy densities of more than 3200 Wh / L make the Mg-S battery very attractive. To achieve the highest possible capacities, the proportion of the active material – sulfur – must be maximized. Due to the electrically insulating nature of sulfur, it must be embedded in a conductive matrix. The proportion of sulfur can be increased by increasing the pore volume of the matrix materials. If a large pore volume is available, a large amount of active material (sulfur) can be infiltrated. Not only pore volumes, but also pore size and pore size distributions play a crucial role.Carbon aerogels are suitable materials not only because of their high electrical conductivity, but above all because of their high porosity (up to 99%), high specific surface area (500-3500 m. 2 / g), high pore volume (2-3 cm 3 / g). The pore sizes can be precisely adjusted both during synthesis and during carbonization. Carbon aerogels can be produced with mono-, bi-, and / or multimodal pore size distributions.

[0012] Particularly attractive for magnesium-sulfur batteries are matrices with a bimodal pore size distribution, which can be adjusted during synthesis via the molar ratios of the reactants. Mesopores in the range of 2 to 20 nm, especially up to 10 nm, are necessary to ensure easy diffusion of the electrolyte into the carbon matrix. Micropores in the range below 2 nm can reduce the so-called polysulfide shuttle. This process occurs during cell discharge, and polysulfides are formed as byproducts. These byproducts exhibit very good solubility in the electrolyte. In particular, the solubility of the long-chain polysulfides is very pronounced and leads to the polysulfide shuttle. The polysulfide shuttle describes the diffusion of polysulfides between the cathode and anode. This mechanism causes the active material (sulfur) required for energy storage to leave the cathode compartment.

[0013] The use of a high-temperature polymer electrolyte membrane fuel cell (HT-PEM-FC) using green hydrogen is of increasing interest, as this type of fuel cell allows the use of methanol as a fuel. This allows for a small tank volume. Due to the increased operating temperature of around 160 °C, a simplified system design is achieved, which also presents some challenges. This results in higher platinum catalyst loadings (1 mg / cm) on the anode and cathode electrodes due to phosphate poisoning. 2 ) are necessary to ensure the required performance.

[0014] The cost of platinum catalysts accounts for a significant portion of the total cost of an HT-PEMBZ stack. A precious metal-free alternative for use as catalysts at the cathode is iron-nitrogen-carbon compounds (Fe-NCs). These exhibit promising catalytic activity for oxygen reduction in acidic environments. Due to their high electrical conductivity, high porosity, high specific surface area, and, above all, their tunable pore size, carbon aerogels are suitable materials to serve as the basis for Fe-NC materials. The use of these materials leads to a significant reduction in costs in HT-PEMBZ production.

[0015] The main disadvantages are the non-adjustable microstructure, especially pore and primary particle size of commercially available materials.

[0016] The object of the present invention is in particular to improve the properties of metal-sulfur batteries, in particular magnesium-sulfur batteries, in particular their cycle stability, and to reduce the costs when used in the HT-PEM fuel cell.

[0017] To achieve the object, the present invention provides a conductive carbon aerogel which comprises a defined pore size.

[0018] A first embodiment of the invention therefore comprises conductive carbon aerogels for use as the cathode of a metal-sulfur battery or a platinum-free or platinum-containing catalyst for a fuel cell with a mesopore size in the range of 2 nm to 20 nm and a micropore size of up to 2 nm. Pore size distributions play a crucial role for both applications. In the case of the metal-sulfur battery, pores in the range of 2 to 20 nm serve as transport channels for the electrolyte; on the other hand, the active sulfur material is enclosed in these pores, thus reducing the loss of active material (so-called polysulfide shuttle effect) during cycling. This leads to greater cycling stability. The presence of larger pores (larger than 20 nm) would promote the polysulfide shuttle effect and thus lead to faster degradation of the cell. In the case of the Pt-free catalyst, pores larger than 20 nm are equally unfavorable.Carbon nanotubes can form in these large pores during doping, which negatively impacts the so-called "oxygen reduction reaction" (ORR) activity. Furthermore, the iron-nitrogen-carbon complexes necessary for high ORR activity form predominantly in the mesopores (preferably in pores with diameters of up to 10 nm). In porous structures with larger pores, the formation of these complexes is hampered due to the larger bond distances between nitrogen and iron, and iron particles can form. The presence of elemental iron also reduces ORR activity because only iron-nitrogen-carbon complexes contribute to the electrochemical activity. The conductivity of the carbon aerogels according to the invention is at least 100 S / m at 1 kN, measured at room temperature, i.e., at 20 °C.Electrical conductivity was investigated using a Loresta GX resistance measurement system (Mitsubishi Chemical Europe). This system is based on the 4-pin surface resistance measurement method based on IS K 7194: 1994 (Testing Method For Resistivity Of Conductive Plastics With A Four-Point Probe Array). Current flows through the outer pins 1 and 4, resulting in a measurable potential difference between the two inner pins. This potential difference depends on the surface resistance of the sample material, which in turn is converted into volume resistivity and thus electrical conductivity. These calculations are implemented in the Loresta GX measurement system. The measurements were performed in the pressure range 3 to 30 MPa.

[0019] The key properties of a porous carbon material are its specific surface area, pore size distribution, and electrical conductivity. When determining the specific surface area, a distinction must be made between the inner and outer surfaces, with the outer surface being almost negligible compared to the inner surface. The inner surface area is determined by the areas of the pore walls. A general distinction is made between micropores (up to 2 nm), mesopores (from 2 nm to 50 nm, up to 20 nm according to the invention), and macropores (from 50 nm, from 20 nm according to the invention). The majority of porous materials, including aerogels, have pores with diameters spanning at least two (bimodal) and often even all three (multimodal) pore size ranges. The micro-, meso-, and macropore volumes are measured using nitrogen sorption at 77 K. The pore size distribution is rarely homogeneous.

[0020] In a preferred embodiment of the invention, the metals of the metal-sulfur battery are selected from alkali or alkaline earth metals or aluminum, particularly preferably selected from magnesium or lithium or aluminum. In a particularly preferred embodiment, the metal-sulfur battery is a magnesium-sulfur battery.

[0021] In a preferred embodiment of the invention, conductive carbon aerogels are obtainable by a process in which resorcinol (R), formaldehyde (F), at least one alkali metal carbonate and / or ammonium carbonate (C) and water (W) are reacted with one another in at least one or more of the molar ratios: n(R) / n(W)= 0.03 to 0.05, in particular 0.036 to 0.044, n(R) / n(C)= 150 to 300, in particular 200 to 275 and / or n(R) / n(F) = 0.25 to 0.9, in particular 0.34 to 0.74, gelled, washed, dried and carbonized.

[0022] The solid content, i.e. the proportion of resorcinol in water (R / W), has an influence on the aerogel properties:

[0023] As the molar ratio n(R) / n(W) increases, so does the electrical conductivity. The catalyst content, n(R) / n(C), also influences the aerogel properties:

[0024] With increasing n(R) / n(C) molar ratio, where C stands for alkali metal carbonates and / or ammonium carbonate, especially sodium carbonate, the electrical conductivity decreases. The formaldehyde content n(R) / n(F) also influences the aerogel properties:

[0025] With increasing n(R) / n(F) molar ratio, the electrical conductivity increases, for the aerogels

[0026] In general, it can be said that mesopore volume and electrical conductivity behave inversely. The preferred combination of both parameters was achieved with molar ratios of n(R) / n(W)=0.036 to 0.040; n(R) / n(C)=250 to 275; and n(R) / n(W)=0.70 to 0.74. Due to their suitable pore size and homogeneous microstructure, carbon aerogels are excellent materials for achieving high platinum and iron-nitrogen catalyst loadings, both for low- and high-temperature PEM fuel cells.

[0027] For use as a cathode in metal-sulfur batteries, the carbon aerogels must be infiltrated with sulfur. Accordingly, a further embodiment of the invention also includes a process in which the carbon aerogel is infiltrated with sulfur following carbonization. This can be achieved, for example, by preparing a mixture of a carbon aerogel and elemental sulfur and grinding it in a mill, melting the mixture in a glass ampoule under vacuum and heating it, and optionally evaporating excess sulfur under a protective gas atmosphere.

[0028] Accordingly, a further embodiment of the invention consists in the intended use of the conductive carbon aerogels for producing a cathode of a metal-sulfur battery according to the invention or a both platinum-free and platinum-containing catalyst of a fuel cell.

[0029] By adjusting the molar ratios, a carbon aerogel with very high electrical conductivity was produced. Previously developed aerogels exhibit lower conductivities.

[0030] The invention thus relates in particular to a conductive carbon aerogel, which can be used as a conductive matrix of a cathode in metal-sulfur batteries or as a starting material for a platinum-free or platinum-containing catalyst in high- or low-temperature polymer electrolyte membrane fuel cells. Embodiment:

[0031] Production of carbon aerooil composites

[0032] • Preparation of the solution o First, 94 ml of distilled water (W) was weighed into a beaker. Then, 30 g of resorcinol (R) was added, and the solution was stirred until the resorcinol had completely dissolved (5 min). Then, 46.1 g of formaldehyde (F) (24% solution in water) was added and stirred for another 5 min. Next, 0.12 g of Na2CCh (C) (solid) was added to the solution. The solution was stirred for another 30 min at room temperature. o Composition: n(R) / n(C) = 250; n(R) / n(F) = 0.74; n(R) / n(W) = 0.038

[0033] Syntheses were performed with n(R) / n(W)=0.032 to 0.044; n(R) / n(C) = 200 to 350; and n(R) / n(F)=0.34 to 0.94.

[0034] • Gelation o The solution was filled into a tightly sealable container (glass or PP) and left to gel in the oven at 60°C for one week.

[0035] • Washing o After one week, the gels were removed from the oven and cooled to room temperature. The gels were carefully removed from the container and placed in a container filled with acetone. The acetone was replaced twice a day. After three days of washing, the washed gel was dried.

[0036] Drying o Drying took place in an autoclave in supercritical CO2. The process parameters were: 100 bar, 60 °C, mass flow rate 15 to 30 kg / h. o After drying, a reddish-brown resorcinol-formaldehyde aerogel was obtained.

[0037] Production of sulfur-carbon composite oils for metal-sulfur batteries

[0038] • Carbonization o The resorcinol-formaldehyde aerogels obtained above were carbonized in a nitrogen atmosphere at 1000 °C for 1 hour. They were physically or chemically activated and doped as needed using conventional methods.

[0039] • Comminution o The carbon aerogels and elemental sulfur were mixed and ground in a vibratory mill at 30 Hz for 30 seconds. The mixing ratio was chosen so that the micropores and mesopores were completely filled with sulfur. Pore volumes were determined via nitrogen sorption, and the required amount of sulfur was calculated.

[0040] • Gas-phase infiltration of sulfur for metal-sulfur batteries, exemplified with magnesium o The sulfur-aerogel mixture was melted under vacuum in a glass ampoule and heated in an oven at 600 °C for 6 h. o If necessary, the sulfur-aerogel mixture could be heated to 330 °C for 1.5 h under an argon atmosphere in a reactor with a cold trap to evaporate excess sulfur. o The sulfur could also be infiltrated in the melt and in the mill if necessary.

[0041] Incorporation of iron-nitrogen complexes for platinum-free fuel cells o Resorcinol-formaldehyde aerogel with the composition n(R) / n(C)=250, n(R) / n(F)=0.74 and n(R) / n(W)=0.038 was used as the starting material for the production of carbon aerogels for fuel cells. The resorcinol-formaldehyde aerogel was milled with a nitrogen precursor (melamine) and an iron precursor (ferrocene) in a mass ratio of 1:1:0.1 in a vibratory mill for 30 seconds at 30 Hz. The mixture was then carbonized at 1000°C at a heating rate of 5K / min under a nitrogen atmosphere for 1 hour. The carbon aerogel was then milled in a vibratory mill at 30 Hz three times for 120 seconds. The material is referred to below as Fe-N-CAl.

[0042] Characterization of carbon aerogels for metal-sulfur batteries

[0043] The aerogels described here (samples CA1-9) possess both a micro- and mesoporous structure (Fig. 1). The microstructure could be adjusted during material synthesis and subsequently by activation (samples CA2, CA7, and CA8) and doping (samples CA2, CA8, and CA9). Activation and doping can be carried out using various known methods, such as thermal treatment. The micro- and mesoporous structure according to the invention enables an increase in stability, since sulfur can be bound in the micropores and pores in the range of 2 nm to 20 nm, in particular 2 nm to 10 nm, are available for electrolyte diffusion. In contrast, the most widely used activated carbon (Ketjenblack®) possesses a predominantly mesoporous structure with pores in the range of 2 to 3 nm and large pores of 20 to 100 nm, which are disadvantageous for the application according to the invention.

[0044] In Fig. 1, the pore size distribution of the carbon aerogels according to the invention (CA2 to 8 activated; CA2, CA8 and CA9 N-doped) and the known activated carbon Ketjenblack® (KB) is compared.

[0045] Table 1 shows that all aerogels possess a very high pore volume, which allowed for high sulfur content and thus high specific capacities. The presence of micropores led to an improvement in the cycling stability of the cell. Furthermore, Table 1 shows that the aerogels also possess good electrical conductivity and that doping with the heteroatom nitrogen is also possible. For this purpose, known methods with various nitrogen-containing compounds (urea, melamine, ammonia) can be used. Results

[0046] The nitrogen present in the structure of the aerogels could be bonded to carbon in various ways (e.g., nitro, amino, or graphitic, pyridinic, and / or pyrrolic nitrogen). Different nitrogen-carbon bonds have different effects on electrical conductivity. While the effect of nitro and amino nitrogen atoms can be neglected, structural nitrogen atoms, such as pyridinic and pyrrolic nitrogen, have a significant influence on the electrical conductivity of the porous carbon. According to the invention, structural nitrogen or nitrogen atoms means that they replace carbon atoms within the carbon lattice and thus do not possess any side groups, thereby contributing p-electrons to the nr-conjugated system. The XPS analysis of a nitrogen-doped aerogel is shown in Fig. 4.The peak at 400.71 eV can be assigned to pyrrolic nitrogen and the peak at 398.77 eV indicates pyridinic nitrogen.

[0047] Table 1 : Properties of carbon aerogels (CA2 to 8 activated; CA2, CA8 and CA9 N-doped)

[0048] For carbon aerogels as cathode material for the Mg-S battery of the exemplary embodiment, the volume ratio between micropores and mesopores in the range greater than 1, in particular in the range from 1 to 6, is particularly advantageous. For use as a catalyst in a fuel cell, the range less than 1, in particular 0.1 to 0.2, is particularly advantageous. This also applies to other meta-II sulfur I batteries.

[0049] Thus, a preferred embodiment of the carbon areogels according to the invention is characterized in that the volume ratio between micropores and mesopores is in the range of less than 1, in particular in the range of 0.1 to 0.2.

[0050] A further preferred embodiment of the carbon areogels according to the invention is characterized in that the volume ratio between micropores and mesopores is in the range greater than 1, in particular in the range from 1 to 6.

[0051] Figure 3 shows the low compressibility of CAI in the range of 3 to 32 MPa. The sample could be compressed by a maximum of 37%, indicating the material's high stiffness. In comparison, a flexible carbon aerogel (DE 10 2018 123 285 Al) is shown, which can be compressed by 77%.

[0052] As described above, the solid content (R / W) influences the aerogel properties: With increasing n(R) / n(W) ratio, the electrical conductivity increases; for aerogels with n(R) / n(W) = 0.036 to 0.044, it is in the range of 350 to 400 S / m at 1 kN.

[0053] The highest mesopore volume (1.45 to 1.74 cm 3 / g) are found in aerogels with an n(R) / n(W) of 0.032 to 0.04. The micropore volume of the aerogels is between 0.13 and 0.16 cm 3 / g. The average pore size is in the range of 13 nm to 19 nm.

[0054] As described above, the catalyst content (n(R) / n(C)) influences the aerogel properties:

[0055] With increasing n(R) / (C) ratio, the electrical conductivity decreases; for aerogels with n(R) / (C)= 200 to 275, it is in the range of 350 to 440 S / m at 1 kN.

[0056] The highest mesopore volume (1.4 to 1.6 cm 3 / g) are found in aerogels with an n(R) / n(C) of 250 to 350. The micropore volume of the aerogels is between 0.13 and 0.16 cm 3 / g. The average pore size increases with decreasing catalyst content and is in the range of 10 nm to 20 nm.

[0057] As mentioned above, the formaldehyde content (R / F) influences the aerogel properties:

[0058] With increasing n(R) / n(F) ratio, the electrical conductivity increases; for aerogels with n(R) / n(F)=0.74 to 0.94, it is in the range of 375 to 570 S / m at 1 kN.

[0059] The highest mesopore volume (1.4 to 2.29 cm 3 / g) exhibit aerogels with an n(R) / n(F) of 0.34 to 0.74. The micropore volume of the aerogels is between 0.15 and 0.17 cm 3 / g. The average pore size increases with increasing formaldehyde content and is in the range of 10 nm to 22 nm.

[0060] In general, it can be observed that mesopore volume and electrical conductivity behave inversely. The best combination of both parameters was achieved with molar ratios of n(R) / n(W) = 0.036 to 0.040; n(R) / n(C) = 250 to 275; and n(R) / n(W) = 0.74.

[0061] Thermogravimetric measurements (Fig. 2) of the sulfur-containing aerogel after gas-phase infiltration demonstrate that carbon aerogels can be used as a matrix for sulfur. The sulfur can be incorporated into both the micropores and the mesopores.

[0062] Characterization of carbon aerogels for fuel cells.

[0063] The aerogels described here (samples CAI and Fe-N-CAl) possess both a micro- and mesoporous structure (Fig. 6). Fig. 6 compares the pore size distribution of the inventive carbon aerogels CAI and Fe-N-CAl. The successful nitrogen and iron doping of Fe-N-CAl reduces the mesopore volume from 1.05 cm 3 / g (CAI) per 0.75 cm 3 / g, especially in the range of 10 to 11 nm pore size (Fig. 6). The micropore volume is 0.13 cm 3 / g (CAI) and 0.15 cm 3 / g (Fe-N-CAl). The specific surface area is 652 m 2 / g (CAI) and 645 m 2 / g (Fe-N-CAl). The electrical conductivity of Fe-N-CAl is 432 S / m, higher than that of CAI at 367 S / m (Fig. 7).

[0064] The scanning electron microscopy images show that the microstructure has not changed due to nitrogen and iron doping (Fig. 8).

[0065] Energy-dispersive X-ray spectroscopy of Fe-N-CAl revealed that iron (approximately 2 wt.%) and nitrogen (3 wt.%) are present in the structure. Furthermore, elemental analysis of Fe-N-CAl revealed that 2.8 wt.% nitrogen and 86 wt.% carbon are present in the structure.

[0066] In general, it can be stated that the nitrogen and iron doping using the new Fe-N-CAl production method was successful. Compared to CAI, the carbon aerogel exhibits a slightly higher electrical conductivity, a nitrogen content of 2.8 wt.%, and an approximate iron content of 2 wt.%. Furthermore, the reduction in mesopore volume compared to CAI indicates the successful nitrogen and iron doping, which, together with the microstructure and electrical conductivity, makes it ideal for use in high-temperature polymer electrolyte membrane fuel cells.

Claims

Patent claims 1. Conductive carbon aerogels for use as a cathode of a metal-sulfur battery or a platinum-free or platinum-containing catalyst of a fuel cell having a mesopore size in the range of 2 nm to 20 nm and a micropore size up to 2 nm.

2. Carbon aerogels according to claim 1, characterized in that the metal is selected from the group of alkali or alkaline earth metals or aluminum, particularly preferably from lithium or magnesium or aluminum, in particular from magnesium.

3. Carbon aerogels according to claim 1 or 2, characterized in that the mesopore size is from 2 nm to 10 nm.

4. Carbon aerogels according to at least one of claims 1 to 3, characterized in that they have a bimodal pore size distribution of mesopores and micropores.

5. Carbon aerogels according to at least one of claims 1 to 4, characterized in that they are doped with iron and / or nitrogen.

6. Carbon aerogels as a catalyst for a fuel cell according to claim 5, characterized in that the volume ratio between micropores and mesopores is in the range of less than 1, in particular in the range of 0.1 to 0.

2.

7. Sulfur-containing carbon aerogels according to any one of claims 1 to 4.

8. Carbon aerogels according to claim 7 as cathode material for metal (magnesium) sulfur batteries, characterized in that the volume ratio between micropores and mesopores is in the range greater than 1, in particular in the range from 1 to 6.

9. A process for producing carbon aerogels according to any one of claims 1 to 8, characterized in that resorcinol (R), formaldehyde (F), at least one alkali metal carbonate and / or ammonium carbonate (C) and water (W) are reacted with one another in at least one or more of the molar ratios: n(R) / n(W)= 0.03 to 0.05, in particular 0.036 to 0.044, n(R) / n(C)= 150 to 300, in particular 200 to 275 and / or n(R) / n(F)= 0.25 to 0.9, in particular 0.34 to 0.74, gelled, washed, dried and carbonized.

10. Process according to claim 9, characterized in that following carbonization, the carbon aerogel is infiltrated with sulfur.

11. A process according to claim 10, characterized in that a carbon aerogel and elemental sulfur are mixed and ground in a mill, the mixture is melted and heated under vacuum, in particular in a glass ampoule, and excess sulfur is optionally evaporated under a protective gas atmosphere if necessary.

12. Process according to claim 9, characterized in that doping with nitrogen and iron is carried out following carbonization.

13. Use of a conductive carbon aerogel according to at least one of claims 1 to 8 or obtainable by a process according to at least one of claims 9 to 12 for producing a cathode of a Magnesium-sulfur battery or a platinum-free or platinum-containing catalyst of a fuel cell.

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