What is Carbon Aerogel?

Carbon aerogels are a category of aerogels and are ultralight porous substances made from largely carbon. Their structure comes from organic aerogels, pyrolysed to strip them of non-carbon molecules. Carbon aerogels are useful in energy storage, catalysis, and clean-up applications because of their large surface area, low density, and conductive nature. They have all of these properties that make them extremely useful industrial and research materials.

Carbon aerogels start with organic aerogel preparation. Organic precursors like esorcinol-formaldehyde (RF), phenolic resins, melamine-formaldehyde, and more are sol-gel polymerised and supercritically dried to produce highly porous organic aerogels. These aerogels are then pyrolysed in an inert atmosphere (nitrogen or argon) at 400 to 1100 °C. The non-carbon parts are thermally destroyed, but still the original aerogel is porous.

Fig.1 The transition from polymer to carbon aerogel leads to a change in morphology^[1].

As it collapses in pyrolysis (where volatile gases - oxygen, nitrogen, and hydrogen - are released), its organic structure dilates into a carbon skeleton. Crystallinity (i.e., better electrical conductivity) can be enhanced by high-temperature treatment between 1400 and 1800 °C. The end product is dense like the precursor, but it has massive mass loss from removing non-carbon elements.

At the nanoscale, carbon aerogels consist of interconnected carbon nanoparticles with diameters between 1-2 nanometers. These particles form a porous network characterized by:

• Surface Area: Typically ranges from 500～800 m²/g, but can be increased to 2500 m²/g through steam or hydrogen activation at 400°C～1000°C.
• Pore Structure: Dominated by mesopores with average diameters of 7-10 nanometers, though micropores (<2 nanometers) can be introduced for enhanced surface area.
• Density: Generally low, depending on the precursor aerogel's density.
• Electrical Conductivity: While carbon aerogels exhibit moderate conductivity, their performance can be fine-tuned by modifying density or introducing conductive additives.

Supercapacitors and Energy Storage Devices

Carbon aerogels are popular in supercapacitors because they have a large surface area and are moderately conducting. They provide the properties to hold and release electrical power efficiently, which is needed for devices such as grids, electric vehicles, and mobile electronics. Due to its high porosity, electrolyte can get through, and thus charge storage capacity is maximised.

Fuel Cells and Catalysis

Porous and electrically conductive, carbon aerogels are perfect for fuel cell catalyst bases. They accelerate reactions by providing easily accessible active sites, which make fuel cell energy efficient.

Desalination and Water Treatment

The large surface area and tunable porosity of carbon aerogels allow them to be applied to capacitive deionisation systems for desalination. Such devices use the conductivity of the material to pull out ions from water, a less costly alternative to other processes.

Fig.2 SEM image of a synthesized carbon aerogel^[2].

• Trade-Off Between Surface Area and Conductivity

Increasing surface area often decreases conductivity due to reduced structural connectivity in low-density aerogels. This limitation necessitates innovative approaches, such as:

(1) Activation Techniques: Steam or hydrogen activation to introduce micropores while preserving conductive pathways.

(2) Metal Doping: Incorporation of conductive materials like gold or silver to enhance charge transport without compromising surface area.

• Scalability of Production

The high cost and complexity of synthesizing carbon aerogels remain barriers to large-scale production. Advances in precursor materials, synthesis methods, and pyrolysis technologies are crucial for widespread adoption.

Keeping on improving, carbon aerogels are going to transform many industries. There are recent experiments with hybrid carbon aerogels containing graphene or carbon nanotubes to add performance. And, finally, we could find efficient and scalable production processes for further new applications in environmental and biomedical sectors.

At Alfa Chemistry, we are specialists in carbon aerogels and have access to innovative products for a wide range of applications. We can bring the magic of innovation and science to the world of application by leveraging the power of these marvellous materials.

Please kindly note that our products and services are for research use only.

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