Upcycling Coffee Waste Into AC/NiO Electrodes for Supercapacitors

Abstract

The conversion of spent coffee grounds into electrochemically active materials offers a route to integrate biomass waste valorization with aqueous energy storage. In this study, activated carbon derived from coffee‐ground waste (CGW‐AC) was prepared by KOH activation and subsequently combined with nickel oxide (NiO) through hydrothermal deposition to produce a CGW‐AC/NiO hybrid electrode. FTIR, Raman, XRD, SEM–EDS, and N 2 adsorption–desorption analyses confirmed the incorporation of crystalline NiO while preserving the hierarchical porous carbon framework. NiO incorporation reduced the BET surface area from 1189.24 to 552.77 m 2 ·g − 1 , indicating partial pore occupation, but substantially increased charge‐storage capability through the additional Faradaic contribution of NiO. In three‐electrode configuration under 1 M Na 2 SO 4 , CGW‐AC/NiO achieved a specific capacitance of 399 F·g − 1 , while CGW‐AC obtained a specific capacitance of 133 F·g − 1 at 1 A·g − 1 . Under two‐electrode configuration, the specific capacitance for CGW‐AC/NiO remains higher, reaching 90 F·g − 1 compared to 62 F·g − 1 for CGW‐AC. A capacitance retention of 87% for CGW‐AC/NiO after 6000 cycles suggests that the NiO present in the carbon structures are active sites that facilitates pesudocapacitance as also demonstrated by CV results. These results highlight the potential of coffee‐waste‐derived AC/NiO for hybrid electrodes in neutral aqueous supercapacitors.