KOH-activated microstructured carbon derived from Asclepias syriaca floss for extraordinary 200k cycle stability in supercapacitors

Abstract

We report a novel carbon material obtained from low-density fibrous fur-like biowaste Asclepias syriaca (milkweed) floss for use as low-cost and efficient electrodes in electrochemical double layer capacitors (EDLCs). Milkweed floss is pyrolyzed to carbon (MW) and activated with widely available and commonly used KOH as a porogen at 700 and 800 °C (MW-1 and MW-2). From Brunauer–Emmett–Teller (BET) analysis, the surface area and pore volume of MW-2 are found to be twice those of MW-1. Morphological and Raman analysis of MW-2 indicates high surface etching/defects. The high surface area and microporosity of MW-2 are due to the vaporized state of metallic potassium during chemical activation. MW-2 exhibits better electrochemical performance in a three-electrode system. A symmetric coin cell (SCC) designed using MW-2 in 1 M KOH exhibits high energy density (ED: 37.6 W h kg⁻¹) and power density (PD: 19.1 kW kg⁻¹) and low solution (R_s: 1.86 Ω) and charge transfer (R_ct: 3.24 Ω) resistance with remarkably high stability after 200k cycles. SCC retains 80% specific capacitance (C_s) with 100% coulombic efficiency and almost negligible change in R_s or R_ct values after 200 000 cycles, thus proving its high supercapacitance efficiency. Furthermore, six fabricated SCCs were connected in series and shown to power a flashlight.