Design of symmetric supercapacitor from biowaste derived carbon for flashlight applications with superior cycle’s stability

Abstract

Extraction of biodiesel from Pongamia pinnata seeds is a vital “Green” synthesis process which is reliable, sustainable, and eco-friendly. The cake obtained during this process is generally utilized as a fertilizer and rich in carbon & nitrogen content. In the present work, initially the material was subjected to carbonization process (PC) was activated with three different porogens such as KOH, KCl, K2HPO4 (K+ as common ion) and labeled as PC-1, PC-2 & PC-3 respectively. The physico-chemical properties of all the carbon materials were investigated by various analytical techniques such as Powder X-Ray diffraction (P-XRD), Brunner Emmett Teller (BET), Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS), Transmission Electron Microscopy and Selected Area Electron Diffraction (TEM-SAED), & Raman spectroscopy. PC-1 exhibited better electrochemical performance than the other activated carbons (ACs) & PC with specific capacitance (Cs) of 253F/g at 2.5 A/g, retained 75% Cs at the end of 10,000th cycle and 100% coulombic efficiency in 1 M KOH solution. The symmetric supercapacitor coin cell (SSC) using PC-1 (1 M KOH) exhibited a high Cs of 112F/g at scan rate of 2 mV/s, a maximum energy density (ED) of 38.6 Wh/kg and power density (PD) of 9 kW/kg. Interestingly, the coin cell demonstrated a total of 100 k cycles at high current density of 25 A/g with time gap of fifteen days for 50 k cycles. Six SSCs connected in series were successfully used to power up a flashlight with 15 white LED’s (each 4 V) connected in series for 3 min.