Upcycling Waste into Carbon Electrodes for Sustainable Energy Storage

The integration of sustainable materials into high-performance energy storage and conversion systems is essential for driving the successful transition to green resource use. In this work, we explore the use of rice husk (RH), an abundant and underutilized agricultural byproduct, as a renewable precursor for synthesizing carbon-based materials suitable for energy storage applications. Two types of materials were derived from RH: carbon aerogels (CAs) and graphene quantum dots (GQDs). The CAs were synthesized through a multi-step process involving two-stage chemical pretreatment to remove lignin, hemicellulose, and silica, followed by gelation, drying, and carbonization. In parallel, GQDs were produced using a simple, solvent-free ball milling method. Both materials were thoroughly characterized using a range of analytical techniques to assess their morphological and structural properties. Their electrochemical performance was then evaluated in lithium-ion batteries and supercapacitors. The GQDs exhibited capacitive behavior with ion intercalation and surface charge accumulation, as demonstrated by cyclic voltammetry and galvanostatic cycling. However, their long-term performance was limited, likely due to poor contact with the electrode matrix and current collector—an issue that may be resolved through optimized formulation strategies. In contrast, the CAs displayed excellent cycling stability, retaining up to 81.2% of their initial capacitance after 10,000 charge–discharge cycles. These findings underscore the potential of rice husk-derived carbon materials as low-cost, sustainable alternatives for the development of efficient and durable energy storage devices.