Sonochemical synthesis of Co3O4/graphene/Co3O4 sandwich architecture for high-performance supercapacitors

Conversion of cobalt from spent LIBs to Co3O4 electrode material for application in supercapacitors

The cathode material of lithium-ion batteries (LIBs) is endowed with valuable metals, such as cobalt. The improper treatment of these batteries pollutes the environment and causes enormous resource waste. Therefore, the recovery of valuable metals from spent LIBs has attracted widespread attention. In this study, Co3O4 electrode materials were prepared by a simple homogeneous precipitation method and heat treatment using a leaching solution of spent LIBs-positive electrode material as the cobalt source. The crystal structure and morphology of the products were examined at different annealing temperatures, and their electrochemical performance was analyzed. The results show that low-temperature annealing contributes to grain refinement. The Co3O4 material prepared at 300°C annealing temperature has a rod-like structure with distinct pores and a specific surface area of 58.98 m2 g-1. Furthermore, electrochemical performance testing reveals that Co3O4 prepared at 300°C displays the best electrochemical performance as an electrode material, with a specific capacitance of 97.93 F g-1 and a cycle retention rate of 79.12% after 500 charge-discharge cycles. These findings demonstrate the feasibility of recycling valuable metal cobalt from spent LIBs cathode materials to produce Co3O4 materials for use as supercapacitor electrode materials, opening up new avenues for the recycling and utilisation of spent LIBs.

Interaction of Co3O4 Nanocube with Graphene and Reduced Graphene Oxide: Adhesion and Quantum Capacitance

The composites on the base of Co3O4 and graphene are in demand in the field of portable, flexible energy storage devices due to their small size, lightweight, big specific capacitance, good cycle stability and appropriate capacitance retention. The synthesis of this material always starts from the treatment of graphene oxide, so as a result, experimenters receive Co3O4 nanocubes incorporated into reduced graphene oxide indicates the presence of different oxygen-containing groups in the compound. This fact may limit the advantages of the considered material. Our theoretical quantum chemical calculations show that the process of Co3O4 incorporation between reduced graphene oxide layers is more energetically favorable in comparison to pure graphene. However, the win in the quantum capacitance in the case of pure graphene is in the range of 300–500 F/g in dependence on the applied voltage. The obtained result may indicate the need for modification of the current methods of graphene/Co3O4 synthesis to improve its application in supercapacitors and lithium-ion batteries.

Microwave-assisted synthesis of hierarchically porous Co3O4/rGO nanocomposite for low-temperature acetone detection

Acetone sensors with high response and excellent selectivity are of enormous demand for monitoring the diabetes. This paper has reported a novel porous 3D hierarchical Co₃O₄/rGO nanocomposite synthesized by a microwave-assisted method, by which Co₃O₄ nanoparticles are rapidly and uniformly anchored on rGO nanosheets. The phase composition, surface morphology of the Co₃O₄/rGO composites and the effect of rGO on their acetone-sensing performance were systematically investigated. The results show that the sample with an optimized content of rGO (Co₃O₄/rGO-1) achieves the highest stability and response to acetone (0.5 ~ 200 ppm) at a relatively low temperature (~160 °C). Also, the Co₃O₄/rGO-1 exhibits a high acetone-sensing selectivity against the gases (or vapors) of H₂S, H₂, CH₄, HCHO, CH₃OH, C₃H₈O and C₂H₅OH. The enhanced acetone-sensing performance of the Co₃O₄/rGO composite can be attributed to the Co₃O₄/rGO p-p heterojunction and the Co³⁺-C coupling effect between Co₃O₄ and rGO, improving transport of carriers. In addition, the unique 3D hierarchically porous structure and large surface areas are favorable to adsorption and desorption of gas molecules. This facile microwave-assisted method provides a charming strategy to develop smart rGO-based nanomaterials for real-time detection of harmful gases and rapid medical diagnosis.