A correlation of surface/textural properties of carbon derived from Musa acuminata stem and its high supercapacitance performance with superior cycle stability

Abstract

Carbonization of variety of biomass materials and activation using metal salts, oxides carbonates etc., aids in increasing its specific surface area (SSA) and activation site density utilized in many applications. Here, Musa acuminata (banana) stem has been carbonized at 450 °C and activated using five different porogens like KOH (C-1), ZnCl2 (C-2), KCl (C-3), NaHCO3 (C-4) & K2HPO4 (C-5) at 750 °C. The physico-chemical properties of these carbon materials have been analysed using P-XRD, SEM, EDS, TEM, SAED, BET and Raman techniques. Apart from usual amorphous graphitic peak in carbon materials, inorganic metal oxides/carbonate/silicate peaks are present due to interaction among biomass derived elements like C, O, K, Mg, Si & P etc., at high temperatures. Among ACs, C-1 shows superior surface properties with very high SSA of 3351 m2 g−1 but gave only specific capacitance (Cs) of 75 F g−1 at 5 A g−1. But C-3 with moderate surface properties exhibited a high Cs of 339 F g−1 at 5 A g−1. C-3 was subjected to continuous charge-discharge cycles at 15 A g−1 indicated 80% Cs retention & 100% coulombic efficiency at 25,000th cycle. A symmetric coin cell (CR2032) fabricated using C-3 in 1 M KOH solution, exhibited a high Cs, specific energy (SE) & specific power (SP) of 88 F g−1 at 2 mV s−1, 62 F g−1 at 1 A g−1 remarkably 34.4 Wh kg−1 and 25.6 kW kg−1 respectively. The coin cell was subjected to enormous number (75,000) of cycles at 25 A g−1 showed Cs retention of 75% with 100% coulombic efficiency. Two-coin cells, each cell operating in the potential range from 0–2 V connected in series are used to power 1-watt LED for 3 minutes.