Ultra-stable capacitance retention over 600 hours via dual cation-coupled interaction in redefined high-quality graphene

Achieving long-life and high-performance aqueous supercapacitors remains a major challenge because of narrow voltage windows and electrode degradation. Here, for the first time, we report the integration of a Rochelle salt (Na⁺/K⁺ tartrate) as a dual-cation electrolyte with high-quality graphene (r²GO) electrodes to unleash an ultra-stable energy storage system. A redefined two-step reduction strategy yields r²GO with an ideal interlayer spacing (0.31 nm), high conductivity, and abundant defect-active sites, effectively suppressing restacking and enabling rapid ion transport kinetics. Density functional theory (DFT) calculations revealed strong coordination between Na⁺/K⁺ ions and tartrate ligands, suppressing parasitic evolution reactions and enabling a widened voltage window. Atomic force microscope (AFM) analysis confirmed the enhanced structural homogeneity and surface roughness of r²GO, whereas scanning electrochemical microscope (SECM) measurements provided direct evidence of the superior charge-transfer kinetics associated with r²GO compared to rGO. Electrochemical testing demonstrated remarkable cycling stability, with r²GO retaining 99% capacitance after 100 000 cycles and exhibiting outstanding long-term stability over 600 hours of continuous operation, far surpassing rGO. To validate practical applicability, an r²GO//KNaC₄H₄O₆//r²GO symmetric pouch-cell device was fabricated, successfully powering portable electronics with excellent flexibility and reliability. The unprecedented combination of Rochelle salt dual-cation electrolytes and r²GO electrodes establishes a new material electrolyte design paradigm for next-generation aqueous supercapacitors, delivering record-breaking durability and real-world applicability.