Hierarchical porous 3D Ni3N-CoN/NC heterojunction nanosheets with nitrogen vacancies for high-performance flexible supercapacitor

In the realm of everyday existence, the allure of flexible portable electronic devices has captured widespread attention. Consequently, the imperative to conceive and fabricate flexible energy storage/conversion systems assumes paramount significance. Transition metal nitrides (TMNs), distinguished by their extraordinary electrochemical properties, emerge as compelling candidates for electrode materials in high-performance energy storage devices. This study undertakes the synthesis of three-dimensional Ni3N-CoN/NC heterojunction nanosheets via a meticulous two-step in situ growth process involving metal organic frameworks (MOFs) on carbon cloth (CC), succeeded by annealing in an ammonia-rich environment. The ensuing nitridation engenders copious ion pathways, engrossing a considerable specific surface area of 233.2 m2 g−1 and endowing nitrogen vacancies in abundance. The augmented conductivity of the nitrogen-vacancy-rich heterojunction is corroborated through density functional theory calculations. Employed as a flexible freestanding supercapacitor electrode, the Ni3N-CoN/NC/CC configuration evinces a marked enhancement in electrochemical performance attributable to its superior intrinsic conductivity and heightened active sites. Notably, the synthesized Ni3N-CoN/NC/CC flexible electrode showcases a remarkable specific capacitance of 468.3 mA h g−1 at a current density of 3 A g−1. Moreover, the integration of the Ni3N-CoN/NC/CC cathode with an activated carbon (AC) anode in a flexible asymmetric supercapacitor (ASC) yields an impressive energy density of 0.2144 mWh cm−2 and a maximum power density of 80 mW cm−2, exhibiting exceptional cycling stability of 92.3% even after 15,000 cycles. The exceptional performance exhibited by the synthesized freestanding Ni3N-CoN/NC/CC composite underscores its tremendous potential in the development of flexible energy storage devices.