Plasma Engineering of Co₄N/CoN Heterostructure for Boosting Supercapacitor Performance

Supercapacitor electrode materials play a decisive role in charge storage and significantly affect the cost and capacitive performance of the final device. Engineering of the heterostructure of metal-organic framework (MOF)-derived transition metal nitrides (TMNs) can be conducive to excellent electrochemical performance owing to the synergistic effect, optimized charge transport/mass transfer properties, and high electrical conductivity. In this study, a Co₄N/CoN heterostructure was incorporated into a nitrogen-doped support by radio-frequency (RF) plasma after simple pyrolysis of Co-based formate frameworks (Co-MFFs), with the framework structure well retained. Plasma engineering can effectively increase the ratio of Co₄N in the Co₄N/CoN heterostructure, accelerating the electron transfer rate and resulting in a rough surface due to the reduction effect of high-energy electrons and the etching effect of ions. Benefiting from the plasma modification, the obtained electrode material Co₄N/CoN@C-P exhibits a high specific capacitance of 346.2 F·g^-1 at a current density of 1 A·g^-1, approximately 1.7 times that of CoN/Co₄N@C prepared by pyrolysis. The specific capacitance of Co₄N/CoN@C-P reaches 335.6 F·g^-1 at 10 A·g^-1, approximately 96.9% of that at 1 A·g^-1, indicating remarkable rate capability. Additionally, the capacitance retention remains at 100% even after 1000 cycles, suggesting excellent cycling stability. The rational design and plasma engineering of the TMN heterostructures at the nanoscale are responsible for the excellent electrochemical performance of this novel composite material.