Further research on versatile carbon superstructures constructed at nanoscale could revolutionize energy solutions and clean up carbon's image.

Burning carbon may no longer be viewed as the popular energy source, but there is still plenty of work to be done in establishing all that sustainably generated power – work that carbon, by its nature, is well-suited to perform.

Superstructured carbons (SSCs) are a unique category of cutting-edge nanomaterial that is fast moving out of the realm of theory and into practical application. With processes no less magical than transforming into graphene, coal or diamonds, carbon can be adjusted at the nanoscale, transforming it into a wide array of highly programmable structures and surfaces.

"[S]uperstructured carbons are a category of carbon-based materials characterized by precisely built pores, networks, and interfaces. This unique category satisfies the particular functional demands of high-performance devices and surpasses the rigid structure of traditional carbons," said Debin Kong et al. in a recent study published in Energy Materials and Devices.

Carbon isn't going away

Carbon alone isn't the enemy of sustainability. Its inefficient misuse as a basic source of energy has overlooked a truly remarkable element that makes it a better tool than fuel – something akin to using a laptop as a paperweight.

With an emphasis on customizability and efficiency, SSCs are a novel method of using carbon more effectively in green energy solutions, relieving design bottlenecks and offering increased functionality and enhanced performance in combination with more standard materials. They also have the potential of utilizing carbon more intentionally to exceed the current efficiency, performance and longevity of energy storage and conversion devices.

This form of nanomaterial customization can modify various metrics such as the specific capacity of the material (the amount of an electrical charge that can be delivered per gram of the material's weight,) increased structural stability, and improved surface utilization and coupling of interfaces for enhanced electron transference.

This means the potential of SSCs to outperform traditional carbon materials in devices like lithium-ion, lithium sulfide and metal-air batteries is really only limited by their possible permutations.

As a bonus, current battery electrochemical designs could profit from SCC integrative networks and pore structures, improving battery performance.

Scaling down, then back up

Nanostructures fall under four categories according to scale: zero-dimensional dots and particles; one-dimensional rods, tubes, fibers, and wires; two-dimensional sheets and membranes; and three-dimensional materials such as graphene aerogels, honeycomb structures, and activated carbon.

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There are several notable characteristics of carbon superstructures, including a) precisely customized pores, b) freely adjusted frameworks – flexible and able to deform, c) spongelike with variable density, and d) highly coupled interfaces that bond seamlessly to other materials.

The arrangement of nanoscale building blocks into superstructures of complex, integrative networks can both inherit the properties of individual module components as well as develop extra synergic benefits, including continuous pathways, more prolific exposed and active surfaces, and robust frameworks with superior mechanical strength, adaptability and efficiency.

"Overall, the concept of SSCs shows a way to solve the problems faced by current carbons, which is important to the practical applications of advanced carbons and their relevant high performance energy related devices in future," the study said.

The need for advanced carbon materials as key components in energy storage and conversion has only become more pressing with increasing demand for more devices with higher performance and efficiency.

Today's technologies are insufficient to handle the oncoming energy transition, requiring continued research to advance design and electrochemical structure.

SSCs are being developed through extensive experimentation and an array of new synthesis strategies to further explore the tunability of carbon's potential structural and functional properties.

These practical studies have resulted in an astounding variety of uniquely functional structures: not just struts and tubes but porous spheres, necklaces, honeycomb, urchins, flowerlike heads full of petals either ruffled or starlike, bulbous flasks, and even virus-like configurations, all by regulating the synthesis conditions.

The research has narrowed down three main structural characteristics:

• Precisely customized pore structures achieve far superior mass transfer and surface utilization compared with conventional carbon surfaces. Using porous carbon as part of the active material in batteries allows active substances and ion-diffusion/uptake kinetics to be captured or filtered, improving surface utilization, mass transfer and specific capacity – the amount of an electrical charge that can be delivered to the material per gram of the material's weight.

• Freely adjusted frameworks are flexible and spongelike, allowing for rapid electron transfer between materials. Interconnected, continuous, and three-dimensional frameworks can flex to densify the carbon structure and produce voids for high-capacity noncarbon materials for high volumetric capacity.

• Highly coupled interfaces further improve electron transfer, improving the overall function and performance of a battery. Interfaces that integrate completely allow for electrochemical reactions to occur more easily and without issues of degradation and separation. Powerful bonding between different components in carbon-based hybrids is vital for ideal electrochemical reactions.

Debin Kong, Tsinghua University

Superstructured carbon has a myriad of potential functionalities that can be tuned to improve upon traditional carbon materials used in energy storage and conversion devices.

What's next?

SSCs are manufactured by methods designed to produce customized structures with various arrangements, components, pore architectures, and morphologies-all with functionalities targeted for specific needs in the fields of energy management and storage applications.

Despite significant progress in discovering the expanding uses of SSCs, their scalable, reproducible, and cost-effective fabrication techniques are still in their infancy. Further study and development are imperative to extend the production scale of this emerging technology from the lab to industrial and commercial performance.

On the horizon developing alongside these nanoscale advancements are technologies like supercapacitors: energy-storage devices demonstrating seconds-long charge and discharge rates, high power output, ultralong service life, wide temperature range, and safety – all desirable prospects in portable electronics, large industrial-scale systems, and hybrid-electric vehicles.

At present, carbon-based supercapacitor electrodes are widely used due to good conductivity, large surface area, and adjustable porosity.

Zinc-ion hybrid capacitors (ZHCs) are another newly emerging energy storage device consisting of a zinc anode and carbon cathode, integrating the merits of both batteries and supercapacitors.

Zinc is considered to be an ideal anode due to its electrical superiority, natural abundance, high safety, and compatibility with aqueous electrolytes. A porous carbon cathode theoretically possesses an infinite cycling life without chemical-phase transformation, substantially revolutionizing the energy-storage metrics of ZHCs.