Electrochemical applications of carbons derived from lignin

Lignin is an abundant natural material that has been studied for several commercial applications. However, this precious organic matter is still underutilized. Now a new review article published in the journal Carbon Neutralizationwritten by Chinese scientists, investigated the electrochemical applications of lignin-derived carbons.

Study: Carbon materials derived from lignin for catalysis and electrochemical energy storage. Image Credit: Rattiya Thongdumhyu/Shutterstock.com

The need for a more sustainable future

Over the past few decades, it has become clear that humanity’s overreliance on fossil fuels is causing environmental damage on a historically unprecedented scale. Carbon emissions have been linked to climate change, rising global temperatures, ocean acidification, altered ecosystems and loss of biodiversity. Moreover, fossil fuels are finite resources, which will lead to a serious energy deficit in the future if they are not phased out in favor of sustainable resources.

Schematic of lignin-derived carbonaceous materials for catalysis and electrochemical energy storage.

Schematic of lignin-derived carbonaceous materials for catalysis and electrochemical energy storage. Image Credit: Wang, H et al., Carbon Neutralization

Several renewable energy technologies have been developed, including solar energy harvesting, wind energy, hydroelectric energy, geothermal energy and energy solutions derived from biomass. Research into sustainable biofuels and alternative green materials has accelerated in recent years.

Lignin and carbons derived from lignin

Manufacturing materials from biomass versus conventional fossil fuel derivatives offers significant advantages for multiple industries. Among the abundant biomass sources that have been explored by researchers, lignin has emerged as a suitable candidate material for building sustainable alternatives.

Lignin is universally abundant and is found in plant cell walls. It is a major component of lignocellulose and provides rigidity to cell wall structures while playing a role in water transport and inhibition of antimicrobial and enzymatic degradation. A key attractant of lignin is the presence of multiple functional groups in its aromatic ring structure, which allows the manufacture of many functional materials.

In addition to natural lignin, the papermaking and biorefining industries annually produce fifty million tons of industrial lignin worldwide. Lignin possesses advantages such as low cost, vast resource reserves, and enhanced aromatization, making it a promising carbon precursor for multiple industrial applications.

Lignin-derived carbons, which offer a possible route to lignin upgrading, have stable physiochemical properties, tunable morphologies, high porosity and good electrical conductivity, and these materials have high specific surface area. The three main types of lignin-derived carbons are porous carbons, which exhibit a range of morphologies, lignin carbon composites, and heteroatom-doped carbons.

The study

The new paper provided a comprehensive review of the current state of lignin-derived carbon research. Recent advances in the use of these innovative materials in electrochemical energy and catalytic storage systems have been explored in depth by the authors, and this is the primary focus of the review.

Lignin-derived carbons applied in several applications have been extensively explored. Heterostructure construction, pore structure adaptation, and heteroatom doping are also discussed in the article. A comprehensive summary of bottlenecks and future research trends is included to guide future studies in this area.

Carbon Lignin Applications

Lignin-derived carbons have been explored in recent research for a variety of catalytic and electrochemical energy storage applications. Lithium-ion batteries, sodium-ion batteries, supercapacitors and thermocatalytic, photocatalytic and electrochemical catalytic applications have all been studied extensively by several teams.

The suitability of these carbonaceous materials for efficient catalysis is due to their stable physico-chemical properties. Their stability and resistance to corrosion in alkaline and acidic media make them attractive substrate materials for this purpose. The tunable microstructures of these materials are an added advantage for catalysis research.

Lignin-derived carbon materials can be prepared as carbon dots, sheet-like porous materials, and 3D porous carbons. Several studies have provided promising results for these highly tunable carbon structures as catalytic materials.

Lignin porous carbons can be used as high-performance electrode materials in supercapacitors due to their abundant and durable resources, low cost, and high carbon content. Several green synthesis methods, such as bacterial activation, have been explored to prepare these materials.

Several researchers have proven the feasibility of using lignin as a raw material for lithium-ion batteries, with cathode and anode materials prepared from lignin-derived carbons. The unique structure of the lignin-derived carbon functional group and its diverse microscopic structure greatly enhance the electrochemical activity. Some studies focus on selecting suitable activators to improve the ordered carbon structure of lignin carbon to further enhance it.

Heteroatomic doping and lignin carbon composites have been widely explored in lithium-ion battery research in recent years. Fully exploiting the modification of lignin’s abundant redox sites to enhance the loading of nanoparticles with lithium storage capabilities is one of the goals of the current study. Research into the use of lignin carbons as cathodes for sodium-ion batteries is currently a key area of ​​electrochemical energy storage research.

Outlook

Lignin is a very promising carbon precursor for use in electrochemical energy storage and catalytic applications. However, some key challenges remain that create bottlenecks and need to be addressed in future work. The development of sustainable, green and highly efficient activation technologies is needed. In addition, the carbonization mechanism of lignin needs to be further investigated.

Another promising area for future work will be the in-depth study of the structure-performance relationship between the carbon microstructure of lignin and practical applications. More advanced characterization methods, such as in situ Raman spectroscopy and X-ray diffraction, will be needed to detect how the carbon structure of lignin changes during energy storage. This will help improve their performance in battery technologies.

Finally, since the composition of lignin varies from source to source, efficient purification methods produce lignin feedstocks from various sources with very similar structures. Overall, the paper provided an in-depth review of current progress in this area of ​​study and will help improve future research on functionalized lignin carbon materials and their applications.

Reference

Wang, H et al. (2022) Carbon materials derived from lignin for catalysis and electrochemical energy storage Carbon Neutralization [online] onlinelibrary.wiley.com. Available at: https://doi.org/10.1002/cnl2.29

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