Carbon aerogels have emerged as a promising class of materials for energy storage applications, particularly in supercapacitors and batteries, due to their unique structural and electrical properties. These materials exhibit an interconnected three-dimensional porous network, high specific surface area, and excellent electrical conductivity, making them ideal candidates for electrode fabrication. Their tunable porosity and surface chemistry further enhance their performance in energy storage systems, offering advantages over conventional carbon-based materials such as activated carbon, graphene, and carbon nanotubes.

The fabrication of carbon aerogel electrodes typically involves a sol-gel polymerization process followed by supercritical drying and carbonization. Resorcinol-formaldehyde precursors are commonly used, where the molar ratio of resorcinol to catalyst controls the pore structure and density. After gelation, the wet gel undergoes supercritical drying with carbon dioxide to preserve the nanostructure, avoiding pore collapse that occurs with conventional drying. The resulting organic aerogel is then pyrolyzed at high temperatures (800–1200°C) in an inert atmosphere to form a conductive carbon aerogel. Additional activation steps, such as chemical activation with KOH or physical activation with CO2, can further increase the surface area to over 2000 m²/g, enhancing charge storage capacity.

In supercapacitors, carbon aerogels serve as high-performance electrode materials due to their ability to store charge electrostatically via electric double-layer capacitance (EDLC). Their hierarchical pore structure—comprising micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm)—facilitates rapid ion transport while providing abundant active sites for charge storage. Studies have shown that optimized carbon aerogels can achieve specific capacitances ranging from 150 to 300 F/g in aqueous electrolytes (e.g., 1 M H2SO4 or 6 M KOH) and 100 to 200 F/g in organic electrolytes (e.g., 1 M TEABF4 in acetonitrile). The presence of mesopores is particularly critical for reducing ion diffusion resistance, enabling high power densities exceeding 10 kW/kg without significant capacitance loss at high scan rates (>100 mV/s).

Compared to other carbon materials, carbon aerogels offer distinct advantages. Activated carbon, while inexpensive and widely used, often suffers from limited conductivity and poorly controlled pore size distribution, leading to lower capacitance and rate capability. Graphene-based electrodes exhibit high theoretical surface area and conductivity but face challenges such as restacking, which reduces accessible surface area. Carbon nanotubes provide excellent conductivity but often lack sufficient porosity for optimal ion accessibility. Carbon aerogels bridge these gaps by combining high surface area, tunable porosity, and robust electrical pathways in a monolithic structure.

For battery applications, particularly lithium-ion and sodium-ion systems, carbon aerogels function as conductive scaffolds or active materials. When used as anodes, their porous structure accommodates volume changes during ion insertion/extraction, improving cycle stability. Sulfur-infused carbon aerogels have also been explored for lithium-sulfur batteries, where the porous network traps polysulfides and enhances conductivity, mitigating the shuttle effect. In these systems, carbon aerogels have demonstrated reversible capacities of 500–1000 mAh/g over hundreds of cycles, outperforming conventional carbon black additives.

Key performance metrics for carbon aerogel electrodes include specific capacitance (F/g), energy density (Wh/kg), power density (W/kg), and cycle stability. In supercapacitors, energy density scales with the square of the operating voltage, making electrolyte selection crucial. Aqueous electrolytes offer higher capacitance but lower voltage limits (~1 V), while organic or ionic liquid electrolytes enable voltages up to 3.5 V, albeit with slightly reduced capacitance. Long-term stability is another critical factor; carbon aerogels typically retain over 90% of their initial capacitance after 10,000 cycles, attributed to their mechanical robustness and resistance to electrochemical degradation.

Recent advancements focus on heteroatom doping (e.g., nitrogen, sulfur) to introduce pseudocapacitance, further boosting energy storage. Nitrogen-doped carbon aerogels, for instance, exhibit enhanced wettability and additional redox-active sites, increasing capacitance by 20–30%. Composite approaches, such as incorporating metal oxides or conductive polymers, also show promise but must balance added pseudocapacity with potential compromises in conductivity or cycle life.

Despite their advantages, challenges remain in scaling up carbon aerogel production cost-effectively. Supercritical drying is energy-intensive, and alternative methods like freeze-drying often yield inferior properties. Research into sustainable precursors (e.g., biomass-derived polymers) and simplified processing routes aims to address these limitations.

In summary, carbon aerogels represent a versatile platform for advanced energy storage, leveraging their unique pore structure and conductivity to outperform traditional carbon materials. Their applicability spans both supercapacitors and batteries, where they address critical needs for high power, long cycle life, and efficient ion transport. Continued optimization of synthesis methods and hybrid designs will further solidify their role in next-generation energy storage technologies.