Design and optimization of binder-free rGO/AlO(OH)/Al2O3 aerogels for energy storage

Abstract

This work reports a facile hydrothermal synthesis of reduced graphene oxide/aluminium oxide hydroxide/aluminium oxide (rGO/AlO(OH)/Al₂O₃) hydrogels without the use of external reducing agents. The resulting hydrogels were transformed into stable, binder-free aerogels via freeze-drying, yielding compact, porous materials with enhanced physicochemical and electrochemical properties. The incorporation of aluminium-based compounds boosted surface reactivity, mechanical stability, and electrolyte interaction of the composite. The aerogels exhibited a high surface area (261 m² g⁻¹) and a permeable microstructure, ideal for supercapacitor (SC) electrodes. Among various compositions, the sample with a 1:1 wt ratio of graphene oxide to Al(NO₃)₃·9H₂O (SAlGH-2) delivered the best electrochemical performance, achieving in a symmetric two-electrode SC a specific capacitance of 131.5 F g⁻¹, an energy density of 36.5 Wh kg⁻¹, and a power density of 328.8 W kg⁻¹ at a scan rate of 5 mV s⁻¹. In parallel, a COMSOL Multiphysics model incorporating pseudocapacitive and electrochemical double-layer capacitance (EDLC) processes provided insights into ion diffusion and interfacial charge storage behaviour during cyclic voltammetry. This performance stems from the synergistic effect of rGO's electric double-layer capacitance, the conductivity and pseudocapacitance of AlO(OH)/Al₂O₃, and the aerogel's hierarchical porous structure. The SC demonstrated excellent durability, with 95.5 % coulombic efficiency and 76 % specific capacitance retention after 10,000 cycles. Structural, spectroscopic, and morphological analyses further validated the aerogel's integrity, underscoring its potential as a high-performance electrode material for advanced energy storage systems.