Facile synthesis of mesoporous ZnCo2O4 anchored on coffee ground/orange peel-derived carbon as an advanced electrode for energy storage

Abstract

The escalating global energy demand and the intermittency of renewable energy sources necessitate the urgent development of sustainable, high-performance energy storage systems, such as supercapacitors. This study aims to engineer a novel hybrid electrode by integrating a redox-active bimetallic oxide with a sustainable biomass-derived carbon scaffold to overcome the energy density limitations of conventional carbon materials. A green and cost-effective strategy was developed to synthesize a CGOP@ZnCo₂O₄ composite by coupling coffee ground/orange peel-derived carbon (CGOP) with ZnCo₂O₄ nanostructures via a wet-chemical route and thermal annealing. The biocarbon framework, derived from sustainable biomass, provides a highly conductive network and an abundance of oxygen- and nitrogen-containing functional groups that facilitate uniform growth and strong interfacial bonding of ZnCo₂O₄. Systematic optimization of the annealing temperature and precursor ratios revealed that the composite prepared at 450 °C with 0.134 mmol Zn(NO₃)₂ and 1.33 mmol Co(NO₃)₂ exhibited a hierarchically porous and well-crystallized architecture. This structural synergy between mesoporous biocarbon and crystalline ZnCo₂O₄ enables rapid ion diffusion and efficient charge transport, resulting in an outstanding specific capacitance of 556.1 F/g at 1 A/g and excellent cycling stability, with 81.1% retention after 5000 cycles. Furthermore, the reduced charge-transfer resistance and pseudocapacitive behavior confirm the improved electrochemical kinetics of the optimized composite. This work demonstrates an environmentally benign route for constructing a high-performance ZnCo₂O₄-based electrode through effective biocarbon coupling, offering a promising pathway for sustainable and scalable energy storage applications.