Functionalized aluminum-graphene oxide for enhanced ion transport in solid polymer electrolytes

This study reports the fabrication and characterization of aluminum-functionalized graphene oxide (GO–Al) composite membranes for solid polymer electrolyte applications. The aim of this work is to investigate how aluminum functionalization modifies the interlayer structure of graphene oxide membranes and influences ion transport behavior. Graphene oxide was synthesized via the Tour method and functionalized with Al³⁺ ions derived from AlCl₃ at different loadings of 3.52, 14.68, and 25.93 wt%. Intercalation of trivalent aluminum ions induced an expansion of the GO interlayer spacing from 0.8125 to 0.8278 nm and promoted the conversion of epoxy (C–O–C) groups into hydroxyl (C–OH) and carboxyl (C–OOH) groups through the formation of stable Al–O–C coordination bonds. These structural modifications enhanced membrane hydrophilicity, structural stability, and ion transport capability. Raman spectroscopy revealed increased structural disorder, while thermogravimetric analysis indicated improved thermal stability with reduced total weight loss. Electrochemical impedance spectroscopy demonstrated a significant enhancement in ionic conductivity from 0.282 to 0.553 S·m⁻¹, attributed to Grotthuss-type ion hopping through hydrated transport pathways. Among the investigated compositions, the GO–Al 25.93% membrane exhibited the most favorable balance between interlayer expansion, defect structure, and ionic transport performance, highlighting its potential as a solid polymer electrolyte.