Green synthesis of carbon aerogels derived from rice husk for advanced supercapacitors

In the perspective of a green transition, coupling the use of sustainable materials with the development of efficient energy conversion and storage systems is highly desirable. Within this context, the present study focuses on the exploitation of rice husk (RH), an abundant agricultural waste, for the synthesis of carbon aerogels (CAs) derived from cellulose, and their application in energy storage devices. The synthetic process shown here includes a two-step pre-treatment removing lignin, hemicellulose, and silica, followed by gelation, drying, and carbonization. Variations on the developed methodology are presented, evaluating their impact on morphology, structure, and electrochemical performances of the CAs. A broad variety of characterization techniques, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray tomography, FTIR, XPS, and Brunauer-Emmett-Teller analysis, has been used to elucidate their morphological and structural properties. The electrochemical performances assessed by cyclic voltammetry and galvanostatic cycling tests demonstrates that when used as electrodes in supercapacitors, some of the obtained CAs display exceptional stability, with a capacitance retention up to 81.2 % after 10,000 cycles. Even without exploiting the well-known synergistic effect observed for composite carbon-based electrodes, the life cycle and capacitance retention we obtained are comparable to those of pyrolytic carbon synthesized from RH in harsher conditions and other 3D cellulose-based composites described in the literature, which proves the robustness of our best pristine CA, and offers a promising perspective on green energy storage solutions.