Facile synthesis of tungsten nitride/carbide quantum dots supported on amorphous carbon for supercapacitor applications

Transition-metal nitrides/carbides are potential electrode materials for supercapacitor applications due to their intrinsic metallic conductivity, potential surface redox, and good chemical stability. In this study, a facile pyrolysis route was applied to synthesize the amorphous carbon (AMC) supported tungsten nitride/tungsten carbide quantum dots (designated as W2N/W2C@AMC). The highly disordered carbon can act as the matrix to anchor W2N/W2C quantum dots with the diameter of 2-4 nm. The specific surface area of the W2N/W2C@AMC composite was as large as 178.47 m2 g-1, which was beneficial to exposure of active sites of the material. The performance of the W2N/W2C@AMC composites for the application of supercapacitors was analyzed by using the electrochemical tests. The W2N/W2C@AMC electrode exhibited a high areal specific capacitance of 1669.6 mF cm-2 at the current density of 1 mA cm-2, corresponding to the gravimetric-specific capacitance of 2921.8 F g-1 at 1.75 A g-1, in a 0.5 M H2SO4 aqueous solution. The asymmetric supercapacitors were fabricated by applying W2N/W2C@AMC and active carbon as the positive and negative electrodes, respectively. The as-fabricated ASC devices exhibited a high energy density of 68.2 W h kg-1 at a power density of 400.1 W kg-1. The outstanding performance of the hybridized electrodes can be attributed to the synergistically utilizing of capacitors contribution originated from the different components, rapid charge transferring, and solidly embedding of W2N/W2C on amorphous carbon. Therefore, the W2N/W2C@AMC composite is a potential candidate for the application of supercapacitors. This work also provides a simple route for the preparation of carbon supported transition-metal nitrides or oxides.