Sustainable biochar for advanced electrochemical/energy storage applications

Biochar is a carbon-rich solid prepared by the thermal treatment of biomass in an oxygen-limiting environment. It can be customized to enhance its structural and electrochemical properties by imparting porosity, increasing its surface area, enhancing graphitization, or modifying the surface functionalities by doping heteroatoms. All these features in biochar are highly desired to successfully utilize it in energy storage (in supercapacitors and batteries) or for hydrogen storage. This review focuses on the preparation strategies of biochar-based materials for energy and hydrogen storage. Also, how the structural properties of biochar can be tuned and optimized for individual applications have been discussed. The hierarchical porous structure of biochar with heteroatom surface functionalities is a desirable feature for supercapacitor application. While for battery applications, graphitic structure and interlayer spacing play a critical role. For H2 storage in biochar, a high surface area with micropore dominant structure and O-rich functional groups are required.