Lignin is an abundant natural material that has been investigated for several commercial applications. However, this valuable organic material is still under-utilized. Now, a new review paper published in the journal Carbon Neutralization, authored by scientists from China, has investigated the electrochemical applications of lignin-derived carbons.
Study: Lignin-derived carbon materials for catalysis and electrochemical energy storage. Image Credit: Rattiya Thongdumhyu/Shutterstock.com
The Need for a More Sustainable Future
In recent decades, it has become clear that humanity’s over-reliance on fossil fuels is causing environmental damage on a historically unprecedented scale. Carbon emissions have been linked to climate change, rising global temperatures, acidifying oceans, changing ecosystems, and loss of biodiversity. Furthermore, fossil fuels are finite resources, which will cause a severe energy gap in the future if not phased out in favor of sustainable resources.
Schematic of lignin-derived carbon 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 power, hydroelectric power, geothermal energy, and biomass-derived energy solutions. Research into sustainable biofuels and alternative green materials has accelerated in recent years.
Lignin and Lignin-derived Carbons
Manufacturing materials from biomass compared to conventional fossil fuel derivatives provides significant benefits for multiple industries. Amongst the abundant biomass sources that have been explored by researchers, lignin has emerged as a suitable candidate material for the construction of sustainable alternatives.
Lignin is universally abundant and found in plant cell walls. It is a major component of lignocellulose and provides rigidity to cell wall structures as well as playing a role in water transport and antimicrobial and enzymatic degradation inhibition. One key attractive element of lignin is the presence of multiple functional groups in its aromatic ring structure, which allows for the manufacture of many functional materials.
Aside from naturally occurring lignin, the papermaking and biorefinery industries produce fifty million tons of industrial lignin globally per year. Lignin possesses benefits such as low cost, vast resource reserves, and enhanced aromaticity, making it a promising carbon precursor for multiple industrial applications.
Lignin-derived carbons, which provide a feasible route toward lignin valorization, have stable physiochemical properties, tunable morphologies, high porosity, and good electrical conductivity, and these materials have a high specific surface area. The three main types of lignin-derived carbons are porous carbons, which display a range of morphologies, lignin carbon composites, and heteroatom-doped carbons.
The Study
The new paper has provided a comprehensive review of the current state-of-the-art in lignin-derived carbon research. Recent advances toward utilizing these innovative materials in electrochemical energy and catalytic storage systems have been explored in-depth by the authors, and this is the main focus of the review.
Lignin-derived carbons applied in several applications have been thoroughly explored. Heterostructure construction, pore structure tailoring, and heteroatom doping are also discussed in the paper. A thorough summary of bottlenecks and future research trends is included, with a view toward guiding future studies in this area.
Lignin Carbon 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 the focus of intense study by multiple teams.
The suitability of these carbonaceous materials for high-performance catalysis is due to their stable physiochemical properties. Their stability and corrosion resistance in both alkali and acidic media means they are attractive substrate materials for this purpose. The adjustable microstructures of these materials are an added benefit 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 sustainable 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 raw materials for lithium-ion batteries, with both cathode and anode materials prepared from lignin-derived carbons. The unique functional group structure of lignin-derived carbon and its diverse microscopic structure significantly improves electrochemical activity. Some studies are focusing on the selection of suitable activators to improve lignin carbon’s ordered carbon structure to improve it further.
Heteroatom 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 focus of the current study. Research into utilizing lignin carbons as cathodes for sodium-ion batteries is a key area of electrochemical energy storage research at the moment.
Outlook
Lignin is a highly promising carbon precursor for use in electrochemical energy storage and catalytic applications. However, some key challenges remain that produce bottlenecks and must be addressed in future work. The development of sustainable, green, and highly-efficiency activation technologies is needed. Additionally, lignin’s carbonization mechanism must be further studied.
Another promising area of future work will be the in-depth investigation of the structure-performance relationship between lignin carbon microstructure and practical applications. More advanced characterization methods, such as in-situ Raman spectroscopy and X-ray diffraction, will be needed to detect how lignin carbon structure changes during energy storage. This will help improve their performance in battery technologies.
Finally, as the composition of lignin varies between sources, efficient purification methods produce lignin feedstocks from diverse sources with highly similar structures. Overall, the paper has provided a thorough review of the current progress in this area of study and will help to improve future research into functionalized lignin carbon materials and their applications.
Reference
Wang, H et al. (2022) Lignin-derived carbon materials 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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