Structural and electrochemical characterization of cellulose derived carbon aerogels

Carbon aerogels (CAs) are unique porous solids made of a network of interconnected carbon structures. Thanks to properties as low density, electrically conductive frameworks, chemical stability, high surface to volume ratio and continuous porosities, they have been widely studied for applications in many fields, e.g. hydrogen adsorbents, supports for catalyst, energy storage. CAs can be fabricated from a wide spectrum of starting materials, such as organic monomers, polymers or biomasses. Regardless of precursors, the production process always involves three fundamental steps: gelation, drying and carbonization. The aim of this work is to study structural, morphological, and electrochemical properties of CAs obtained by cellulose purified from Rice Husk (RH). RH is the outer covering of rice and a green, economical, nontoxic, and biodegradable source of carbon. It is mostly made of cellulose, lignin and hemicellulose, but also of inorganic components as silica. Purification of cellulose occours with a two step pretreatment with sodium chlorite in acetic acid and sodium hydroxide. The gel is obtained dissolving cellulose in a solution of sodium hydroxide and urea in water and regenerated with pure water, freeze dried and carbonized in Ar atmosphere at 800°C. A full characterization of the thus obtained CAs has been performed using different techniques, aimed at understanding behaviour and best potential applications. Morphology, composition, and dimensions have been evaluated by scanning electron microscopy, X-ray tomography and energy dispersive X-ray spectroscopy. X-ray diffraction and Raman spectroscopy have been used to investigate structures and graphitization. Electrochemical behaviour has been studied with cyclic voltammetry and ciclations in order to further evaluate CAs performance as electrodes. This study represents a first step to fully understand the potential of rice husk as a green source for CAs and its most promising applications, and it paves the way to additional investigations towards the valorization of a low value agricultural waste.