Activated carbon (AC) electrodes from coffee waste (CW) were earlier assessed in supercapacitors, but showed lower supercapacitor performance, in terms of specific capacity (C_s), specific power (P_s) or both, compared to other biowastes. This work describes how CW-based AC electrode performance may be improved, if carefully prepared. Careful processing yields higher graphitization, carbon content (aromaticity), conductivity and porosity free of any residues. Thus, AC electrodes will exhibit higher C_s and P_s simultaneously. CW was first pyrolyzed (C_Pyrol), and then chemically activated by ZnCl₂ (AC_Chem).  Both materials were characterized using SEM, TEM, BET, FT-IR spectra, Raman spectra and XRD.  The AC_Chem exhibited much higher graphitization, crystallinity, specific-surface area (SSA), porosity and conductivity. From cyclic voltammetry, the AC_Chem electrode exhibited C_s 261 F/g, energy density 18.3 Wh/kg and P_s 360 W/kg at 0.33 A/g. From galvanostatic charge-discharge, a stable C_s of 150 F/g at 0.33 A/g over 5,000 charge discharge cycles. From electrochemical impedance spectroscopy, the Cs was ~180 F/g, with low equivalent-series resistance (ESR) of 0.56 Ω at frequency 0.01 Hz, compared to literature. The AC_Chem electrode was superior to C_Pyrol electrode and to earlier CW-based AC counterparts, with much lower resistance. Moreover, the electrode competed with other biowaste-based electrodes.

Title

Processes

Publisher

MDPI

Publisher Country

Switzerland

Indexing

Thomson Reuters

Impact Factor

2.8

Publication Type

Both (Printed and Online)

Volume

12

Year

2024

Pages

2832