Rational design and electrochemical characterization of a 3D cobalt phosphate/MXene/vertical graphene nanohills (VGNHs) heterostructure for supercapacitor applications

초록

Transition metal phosphates (TMPs) are promising electrode materials for supercapacitors (SCs) due to their robust redox chemistry; however, the slow kinetics and low efficiency limit their energy storage capabilities. To overcome these challenges, we developed a binder-free Co-3(PO4)(2)/MXene/vertical graphene nanohills (VGNHs) nanocomposite (designated as the CMVC-series) on a carbon cloth (CC) substrate using simple chemical deposition approaches. In this synergistically integrated heterostructure, the Co-3(PO4)(2) nanospheres are directly grafted onto a highly conductive MXene/VGNHs framework, which provides abundant active sites, continuous charge transfer pathways, and exceptional mechanical strength, thereby improving the pseudocapacitive properties through dual charge storage mechanisms. Owing to these structural advantages, the CMVC-4 electrode attained a remarkable specific capacity of 924 C/g (256 mAh/g, 3.207 F/cm(2)) at a current density of 2.0 A/g based on the total mass of Co-3(PO4)(2)/MXene/VGNHs and retained 95 % of its initial capacity over 10,000 cycles. Moreover, CMVC-4 achieved a shorter relaxation time (tau(0)) of similar to 1.67 s, which indicates that such improved performance was due to rapid surface Faradaic processes enabled by the tailored nanospheres with a nanohills/nanosheets morphology of the nanocomposite. To demonstrate its potential for future device integration, we constructed a prototype solid-state symmetric SC using CMVC-4 electrodes and a PVA-KOH gel electrolyte. Operating within a potential window of + 1.3 V, this device delivered a high energy density of 12.3 Wh/kg and a power density of 1301.6 W/kg, retained 92 % of its capacity over 10,000 cycles, and successfully powered light-emitting diodes (LEDs). This study presents the Co-3(PO4)(2)/MXene/VGNHs nanocomposite as a high-performance electrode material, thereby providing a foundational platform for the future development of advanced, compact energy storage devices, subject to subsequent evaluations.

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