Trash to Treasure: Waste Eggshells Used as Reactor and Template for Synthesis of Co₉S₈ Nanorod Arrays on Carbon Fibers for Energy Storage

Abstract

The disposal of eggshell waste is an environmentally and economically challenging problem. We demonstrate here a novel application of waste eggshell as a multifunctional reaction system to regulate the reactants and pH inside the reactor and using eggshell membrane as protein-based and active substrates to collect the nanostructures formed in a controlled environment. We outline an idea of transferring waste eggshell (or "trash") into a unique reaction system (or "treasure") for the synthesis of 1-D nanorod arrays on eggshell membrane protein fibers. Subsequently, the intrinsic sulfur element contained in the eggshell membrane protein fibers is utilized to transform the Co(OH)2 nanorod arrays into Co9S8 nanorod arrays. Meanwhile, the protein fibers are in situ carbonized into carbon fibers. The as-synthesized composite of crystalline Co9S8 nanorod arrays on carbon fibers is demonstrated to be a potential electrode for both lithium-ion and sodium-ion batteries. The idea of in situ carbonization and sulfurization based on proteins could be generalized for the synthesis of a composite of carbon and sulfides.