Hierarchical polypyrrole@cobalt sulfide-based flexible on-chip microsupercapacitors with ultrahigh energy density for self-charging system

Herein, we prepare the unique hierarchical polypyrrole@cobalt sulfide (PPy-hs@CoS) hollow sphere-based nanofilms as interdigitated electrodes for flexible on-chip micro-supercapacitors (MSC). Benefiting from the excellent flexibility and high electrical conductivity of PPy-hs combined with the great electrochemical activity of CoS, such PPy-hs@CoS composite material can not only inhibit the volume expansion of PPy but also promote the diffusion of the electrolyte ions. The PPy-hs@CoS film-based electrode delivers a greatly improved specific capacitance and small resistance. Density functional theory calculations infer that OH⁻ prefers to bind to PPy on CoS@PPy and confirms the synergistic effect of each component for enhanced reaction kinetics. A quasi-solid-state on-chip flexible asymmetric MSC based on PPy-hs@CoS and activated carbon (AC) microelectrodes exhibits large areal-specific capacitance (131.9 mF/cm² at 0.3 mA/cm²), ultrahigh energy density (0.041 mWh/cm²@0.224 mW/cm² and 25.6 mWh/cm³@140.6 mW/cm³), and long cycle lifespan. We demonstrate the possibility to scale up the PPy-hs@CoS nanofilm microelectrode by arranging two of our asymmetric MSC in series and parallel connections, which respectively increase the output voltage and current. A self-charging system by connecting our asymmetric MSCs with a piece of commercial solar cells is developed as a potential possible mode for future highly durable and high-voltage integrated electronics.