Soybean carbon coated zinc oxide nanoparticles as a cathode in aluminium ion battery

Abstract Aluminium–ion and aluminium–air batteries offer potential as cost-effective and sustainable energy storage systems, but their commercial application remains limited due to challenges such as aluminium anode self-corrosion, slow oxygen reduction reaction (ORR) kinetics, and the use of expensive catalysts. In this study, nitrogen-rich soybean carbon-coated zinc oxide (C-ZnO) nanoparticles were synthesized and incorporated into a polyvinyl alcohol (PVA) matrix to form a cathode film. The composite was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Elemental analysis revealed 4.68% nitrogen in the soybean carbon. XRD confirmed crystalline ZnO (peaks at 2θ = 31.84° to 61.2°) and hexagonal carbon structure (2θ ≈ 26.32°), with a particle size of 27.41 nm. SEM images showed nanofibrous morphology, and TGA indicated four-stage weight loss with 43.56% residue at 800 °C. The particle size and polydispersity index were 5432.236 nm and 0.1, respectively. Electrochemical behaviour was studied using cyclic voltammetry, and a prototype aluminium-ion battery was assembled. The battery powered a red LED for 86 hours continuously at 1.8 V with a 30 mA discharge current, achieving 54 mW power. Using 4.38 g aluminium anode and 1.45 g cathode material in 4 M KOH, the battery delivered a specific capacity of 326 mAh g⁻¹ and energy density of 3243 Wh kg⁻¹. This work demonstrates a promising bio-derived cathode approach for aluminium-based batteries