Al³⁺ ion storage behaviour in organic-inorganic vanadyl acetate with aqueous and gel electrolytes

This report explores the Al³⁺ ion storage capacity of organic-inorganic vanadyl acetate (VA), as well as its composites with reduced graphene oxide (rGO/VA) and carbon nanotube (CNT/VA), using different aqueous and gel electrolytes. It is found that at lower scan rates, VA’s charge storage is mainly governed by diffusion, while at higher scan rates, both diffusion and surface processes play a role. The initial discharge specific capacitances for VA, rGO/VA and CNT/VA at a current density of 1 Ag^− 1 were calculated as 543 Fg^− 1, 614 Fg^− 1 and 1020 Fg^− 1 respectively, in a 1 M AlCl₃ aqueous electrolyte. While, there was an early drop in capacitance during cycling in 1 M AlCl₃, this issue was alleviated by increasing the pH of the solution and using a gel electrolyte. Thus, in a 1 M AlCl₃/NH₄OH (aq, pH = 3.6) electrolyte, VA delivered a specific capacitance of 852 Fg^− 1, remaining at 72 Fg^− 1 after 100 cycles. Similarly, with a 1 M AlCl₃/NH₄OH/PVA (gel, pH = 3.4) electrolyte, the initial discharge specific capacitance reached 1351 Fg^− 1 for the first cycle, holding at 80 Fg^− 1 after 100 cycles. Structural and morphological changes in VA during the electrochemical process were examined using ex-situ XRD, Raman, and FESEM analysis.