Towards Tuneable Lignin-Derived Activated Carbons for Energy Storage Applications

A significant shift from fossil fuels to clean technology is required to reduce carbon dioxide emissions, and limit the effects of global warming. There is one class of materials which offers potential solutions in many areas of energy storage, from supercapacitors to Li-battery materials, and materials for adsorptive storage of gases, such as methane and hydrogen. These so-called nanoporous carbons have a lot in common with Leerdammer cheese. Although these materials are neither bright yellow nor edible, they are full of thousands of nano-scale sized pores. The performance of these carbon materials is strongly correlated to the size and geometry of their pores.

Lignin, an integral part of lignocellulosic biomass, is produced in large quantities by the paper and pulping industry. The wide-spread availability and low cost of lignin makes this a promising feedstock for industrial-scale production of activated carbons. Uniquely, the lignin structure varies depending on the plant species it is isolated from. This leads to the exciting possibility we will be able to tune the activated carbon structure, including the size and shape of its pores, simply by choosing the feedstock. The structure of four lignins systematically isolated using the same method, but from different feedstocks, was investigated. Despite a similar chemical composition, it became clear that each lignin was composed of different numbers of aromatic units. After lignin carbonisation, only the aromatic backbone remains, thus lignin from different feedstocks is likely to produce carbons with distinct structures. Initial experiments support this possibility, since the lignins exhibited different behaviours after carbonisation. This work shows promise for using selection of the biomass feedstock to tune activated carbons porosity for different applications.