Rice husk derived carbon aerogels for supercapacitor

Carbon aerogels (CAs) have gathered attention since their first fabrication in 1980s thanks to outstanding physical and chemical properties like low density, high conductivity, chemical stability, high specific surface and a 3D porous structure. CAs can be obtained from different precursors such as organic monomers, biomasses, polymers or carbon nanostructures like graphene or nanotubes. Regardless of the starting material, they are usually prepared in three steps, i.e. gelation, drying and carbonization. [1] Their abovementioned properties derive from the aerogel microstructure, which is a network of interconnected particles, and make CAs promising materials for many different applications, e.g., as adsorbents and supports for catalysis, electrodes for rechargeable batteries and supercapacitors. . In particular, the latter are especially relevant devices in electrochemistry due to their high energy density, power density, and long life. [2] The aim of this work is to build a light, stable and highly conductive CAs-based supercapacitor electrode made of cellulose purified from rice husk (RH). RH is an agricultural waste that represents a green and virtuous source of carbon, it is inexpensive, abundant, and eco-friendly. It is mostly made of cellulose (≈38%wt), lignin (≈22% wt), hemicellulose (≈18% wt), silica (≈20 wt% wt) and inorganic components. Due to its nontoxic nature and its good biodegradability, the use of cellulose to prepare CAs has already been reported. [2,3] The process hereby presented involves a two-step pretreatment, respectively with NaOH and with NaClO2 in acetic acid, aimed at the removal of silica, inorganic impurities and other carbonaceous components, i.e. lignin and hemicellulose. In order to form a gel, the purified cellulose thus obtained is dissolved in a solution of NaOH, urea and water at 0°C, then the gel is aged and regenerated with distilled water, freeze dried at -50°C for four hours and lastly carbonized in inert atmosphere. and applied as electrode. Preliminary results obtained by testing our material as electrode pave the way to the application of rice husk cellulose derived CAs in supercapacitors and to different electrochemical devices.