A 2.0 V capacitive device derived from shape-preserved metal nitride nanorods

A high working voltage and fast charging/discharging capability are important to a supercapacitor device in order to achieve decent energy densities with high power. In this work, we report 2.0 V quasi-solid-state symmetric capacitive device based on Fe₂N-Ti₂N (FTN) core-shell nanorod array electrodes. Through a surface protection by a thin and ultra-stable Ti₂N shell, Fe₂N converted from its oxyhydroxide precursor inhibits the original nanorod structure. Due to advantageous features of these core-shell metal nitride electrodes (e.g., high conductivity, structure stability, direct current path), the symmetric device permits ultrahigh scan rates (up to 50 V s^-1) and delivers fairly stable capacitance in long-term cycles (~82 F g^-1 with ~99% capacitance retention in 20,000 cycles). As a result, the supercapacitor exhibits an impressive energy density of ~48.5 W h kg^-1 at the power of 2700 W kg^-1. These results demonstrate the potentialities of metal nitride nanorods array for high energy density capacitive device.