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

This work reports a facile hydrothermal synthesis of reduced graphene oxide/aluminium oxide hydroxide/aluminium oxide (rGO/AlO(OH)/Al 2 O 3 ) 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 m 2 g -1 ) and a permeable microstructure, ideal for supercapacitor electrodes. Among various compositions, the sample with a 1:1 weight ratio of graphene oxide to Al(NO 3 ) 3 ·9H 2 O (SAlGH-2) delivered the best electrochemical performance, achieving in a symmetric two-electrode supercapacitor (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)/Al 2 O 3 , 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. Binder-free rGO/AlO(OH)/Al 2 O 3 aerogels were synthesized via hydrothermal and freeze-drying methods, forming lightweight, porous structures with high surface area. Used in supercapacitors, these aerogels exhibited high specific capacitance, energy density and long-term stability. COMSOL Multiphysics modelling visualised the dynamic behaviour of ion transport and charge storage, capturing both capacitive and Faradaic contributions to overall performance. These results highlight the structural and electrochemical advantages of the aerogels for energy storage and conversion applications. • Novel binder-free rGO/AlO(OH)/Al 2 O 3 aerogels with high surface area and structural stability. • Optimized aerogel delivers 131.5 F g -1 capacitance and 36.5 Wh kg -1 energy density in aqueous symmetric supercapacitors. • Supercapacitor retains 76% capacitance after 10,000 cycles with 95.5% coulombic efficiency. • A COMSOL Multiphysics model incorporating ion diffusion and pseudocapacitive kinetics simulated the cyclic voltammetry behaviour of the supercapacitor.