Transforming hazelnut shell waste into high value electrode materials through bismuth oxide functionalization for supercapacitor applications

Abstract

The development of sustainable and low-cost electrode materials from biomass has gained significant interest for advanced energy storage applications. In this study, high-surface-area activated carbon (HSAC) was synthesized from hazelnut shells through pyrolysis followed by KOH activation. To improve electrochemical performance, a nitrogen-enriched Bi2O3-decorated hybrid composite (Bi2O3@HSAC) was prepared via a hydrothermal method. The structural, morphological, and surface properties of the materials were characterized using XRD, SEM-EDS, FTIR, Raman spectroscopy, XPS, and N2 adsorption-desorption analyses. The results confirmed the successful incorporation of Bi2O3 onto the porous carbon matrix while preserving its hierarchical pore structure and high surface accessibility. Electrochemical investigations in 1 M H2SO4 demonstrated typical capacitive behavior for both electrodes. The Bi2O3@HSAC electrode exhibited nearly twice the specific capacitance of pristine HSAC at 1.0 A g(-1), indicating the positive contribution of Bi2O3 to charge storage. Furthermore, the hybrid electrode retained 90.7% of its initial capacitance after extended cycling, confirming its excellent stability. A symmetric supercapacitor assembled with the optimized electrode delivered an energy density of 3.2 Wh kg(-1) at a power density of 262 W kg(-1) and maintained 1.2 Wh kg(-1) at 540 W kg(-1), demonstrating good rate capability. The improved electrochemical performance is attributed to the synergistic effect between the electrical double-layer capacitance of the biomass-derived porous carbon and the pseudocapacitive contribution of Bi2O3. These findings provide an effective approach for converting agricultural waste into value-added electrode materials and demonstrate the potential of hazelnut shell-derived Bi2O3@HSAC composites for sustainable supercapacitor applications.