Washing-Engineered Graphene Aerogels: From Acid Etching to Electrolyte-Targeted Energy Storage Performance

The porous structure and surface chemistry of graphene aerogels (GAs), critical to their energy storage performance in aqueous supercapacitors, can be effectively modulated by postoxidation washing treatments. In this study, three graphene aerogel samples, namely water-washed graphene aerogel (GA-W), acid–water cowashed graphene aerogel (GA-A/W), and acid-washed graphene aerogel (GA-A), were prepared through hydrothermal assembly of graphene oxide with different washing protocols. Experimental characterizations and density functional theory calculations confirm that residual protons trigger the transformation of carbonyl groups to hydroxyl moieties, accompanied by lattice distortion and pore collapse. Electrochemical measurements show that GA-W with a microporous structure and intact sp2 network achieves a specific capacitance of 319 F g–1 at 1 A g–1 in 6 M KOH electrolyte via dominant electric double-layer capacitance. Benefiting from high mesopore fraction (86.7%) and moderate carbonyl retention, GA-A/W delivers a capacitance of 248 F g–1 at 1 A g–1 in 0.5 M (NH4)2SO4 electrolyte, owing to matched ion transport channels and enhanced proton-coupled electron transfer (PCET) pseudocapacitance. This work elucidates the proton-induced structural degradation mechanism of GAs and proves that washing engineering is a facile and scalable approach to develop electrolyte-adaptive carbon electrodes for aqueous supercapacitors.