Green and facile fabrication of hierarchical N-doped porous carbon from water hyacinths for high performance lithium/sodium ion batteries

Exploitation of carbon materials by efficient and environment-friendly methods is of great scientific and technical significance in meeting the demands of energy storage devices. Here, we demonstrate a low-cost, simple and readily scalable approach for the synthesis of hierarchically N-doped porous carbon (NPC) from an eco-unfriendly and fast-growing hydrophyte, i.e., the stem medulla of water hyacinths. During carbonization treatment, the alkaline or alkali earth elements that naturally exist within the stem medulla can induce the formation of pores accompanying a self-activation process analogous to KOH-activation of carbon materials. The optimized NPC shows a specific area as high as 1005 m(2) g(-1) with a hierarchical porous structure, and manifests excellent electrochemical performance as anode materials for both Li-ion batteries (LIBs) and Na-ion batteries (SIBs), in terms of specific capacity, cycling stability, and rate capability, benefitting from the synergistic effects of the hierarchical porous structure and N-doping.