From seaweed to energy storage

Using seaweed to build batteries and capacitors might sound strange, but it may soon be a reality. Researchers are using carbohydrate molecules extracted from red algae seaweed to form complex structures that have high surface areas and readily controlled arrangements of pores. The potential for their use as energy storage devices is promising.

The raw material for the research is , a family of linear sulfur-bearing carbohydrate molecules readily extracted from seaweeds. Carrageenans are already harvested for use as gelling, thickening and stabilizing agents in the food industry.

“Current carrageenan production is more than 37,000 tons per year,” says researcher Dongjiang Yang of  in China. There is therefore a ready supply chain of the raw materials for the applications Yang and his colleagues discuss in the journal .

The raw material is converted into carbon-based “hierarchical” structures, which consist of a complex network of nested structures. This hierarchical structural arrangement is the key to squeezing a large carbon-based surface area into a small overall volume.

Further useful complexity is provided by networks of pores whose sizes can be controlled during the fabrication process. A structure built from carbon alone, however, is not sufficient. The necessary electrical storage characteristics depend on including iron ions and sulfur atoms at appropriate intervals.

The manufacture of the innovative materials is achieved by dropping carrageenan into an iron-bearing solution to form a watery “”. This is then washed and dried, and then the hydrogel is  at temperatures ranging from 300 to 600 degrees Celsius, depending on the precise structures desired.

Further treatment with acid and alkali, then heating at 800 degrees Celsius, yields the final product, which is technically known as “3D hierarchical macro-meso-microporous sulfur-doped carbon ” or just HPSCA.

“We have shown that HPSCAs can act as electrodes for high-performance energy storage devices – batteries and supercapacitors, in simple terms,” says Yang.

He points out that over the past decade hierarchical porous materials have attracted significant interest due to their immense potential in energy storage, and also in other fields including catalysis and selective gas adsorption.

“Our method offers a green and sustainable route to these high-performance energy storage materials,” Yang emphasizes. He adds that the team became interested in seeking this alternative route due to the complexities and associated high costs of traditional methods.

Yang acknowledges that further work is needed to make the process ready for large-scale commercialization. But he is optimistic that his new route to HPSCAs could have a bright future in the battery and  industry. It also seems likely that other applications in catalysis and gas treatment, for example, could follow.

Article details: Yang, D. et al.: "From double-helix structured seaweed to S-doped carbon aerogel with ultra-high surface area for energy storage" Energy Storage Materials (2019).