Hybrid energy storage using nitrogen-doped graphene and layered-MXene (Ti3C2) for stable high-rate supercapacitors

Abstract

Easy disposal of supercapacitors at their end-of-life is a rarely discussed aspect in research literature. Due to thez demand for stable high-powered devices with significant specific energy, a cost effective and sustainable approach using 2D materials is presented in this work. N-doped graphene synthesized from a cheap and facile exfoliation of graphite in an aqueous salt electrolyte is combined with layered MXene nanostructures in an asymmetric hybrid design to exploit the merits of these electrode materials. The device was tested in a non-corrosive neutral KNO3 aqueous electrolyte and exhibited noteworthy performance. The hybrid device could operate at 1.6 V with a remarkable stability demonstrated by floating tests performed for >3 days and cycling for 25,000 cycles. A 90.4% capacitance retention with only a 0.5% loss in Coulombic efficiency was observed confirming the outstanding stability of these materials in a neutral aqueous electrolyte. The device is able to deliver an average specific energy of 28 Wh kg−1 and a maximum power of 16 Kw kg−1. The device performance is linked to the dopants in the exfoliated graphene sheets and abundant reactive sites in the layered MXene nanostructure which gives rise to rapid ion transport dynamics and efficient charge storage. The findings of this work will pave new routes in achieving safe and reliable supercapacitors using non-corrosive and eco-friendly materials with comparable electrochemical performance to conventional devices.