Ultrasound-assisted uniform deposition of Au nanoparticles on biomass derived activated carbon for high performance supercapacitors.

Biomass-derived activated carbon is a promising sustainable electrode material for supercapacitors; however, improving its electrochemical performance requires effective surface modification while preserving its porous structure. Gold nanoparticles (AuNPs) are attractive modifiers, but their effectiveness strongly depends on particle size and dispersion. In this study, high-frequency ultrasonic irradiation (200 kHz) generates acoustic cavitation to promote AuNP deposition on rice-straw-soluble-derived activated carbon, and its effect is compared with conventional magnetic stirring. Cavitation-induced micro-mixing and enhanced interfacial mass transfer facilitate Au precursor transport and nucleation while suppressing particle growth and coalescence. A control experiment demonstrates that ultrasonic irradiation alone increases structural disorder without improving capacitive performance, indicating that the beneficial effect of ultrasound primarily arises from its role in controlling AuNP deposition. Quantitative TEM analysis shows that ultrasound-assisted deposition produces smaller and more uniformly distributed AuNPs (26.88 nm) than magnetic stirring (81.79 nm), which causes pronounced agglomeration. The optimized ACAu-20-60-ul electrode retains a high specific surface area of 2180 m2 g-1 and delivers 387F g-1 at 0.5 A g-1, representing a 66% enhancement over pristine AC700 (233F g-1). In a symmetric device, ACAu-20-60-ul achieves 160F g-1 at 0.5 A g-1 and 22.2 Wh kg-1 at 500 W kg-1, with 96.5% capacitance retention after 5000 cycles. These results demonstrate that acoustic cavitation effectively controls AuNP formation and dispersion, providing an effective sonochemical strategy for engineering high-performance biomass-derived carbon electrodes.