Unveiling Faradaic Storage of MgCo ₂ S ₄ /rGO Composite Nanostructure as Positive Electrode for Hybrid Supercapacitors

The present work develops a facile ultrasonication method to fabricate hybrid supercapacitor (HSC) positive electrodes based on pristine MgCo ₂ S ₄ and MgCo ₂ S ₄ /reduced graphene oxide (rGO) composite. The rGO has been synthesized from spent graphite in lithium‐ion batteries (LIBs) without any purification process. This inventive work initiates waste utilization to wealth strategies in the area of supercapacitor research, and the presence of rGO boosts the capacitive performance of the fabricated electrode. In this way, economically beneficial and the achievement of closed‐loop LIB recycling may be fulfilled with a mitigation of the environmental issues caused by spent LIB components. Morphological analysis establishes the homogenous distribution of MgCo ₂ S ₄ nanoregime particles on the surface of the rGO framework, and conductive networks are tuned via promotion of the electroactive sites, thereby speeding ionic migrations across the interface. Promisingly, the designed MgCo ₂ S ₄ /rGO composite delivers the specific capacity of 452 Cg ⁻¹ (1005 Fg ⁻¹ ) at 1 Ag ⁻¹ with excellent rate capability. The HSC device has been fabricated with the use of as‐prepared MgCo ₂ S ₄ ‐based nanostructures. The storage performance of 151 Fg ⁻¹ at 1 Ag ⁻¹ is marked for composite MgCo ₂ S ₄ /rGO HSC, whereas the pure MgCo ₂ S ₄ device shows a lower storage value (47 Fg ⁻¹ ). The proposed methodology is a facile and alternate approach to fabricate MgCo ₂ S ₄ /rGO nanostructure, establishing the higher electronic transport in the network as well as promoting redox active sites for faster reactions toward upcoming charge storage applications.