Tungsten Nitride Nanodots Embedded Phosphorous Modified Carbon Fabric as Flexible and Robust Electrode for Asymmetric Pseudocapacitor.

Abstract

Owing to the excellent physical properties of metal nitrides such as metallic conductivity and pseudocapacitance, they have recently attracted much attention as competitive materials for high-performance supercapacitors (SCs). However, the voltage window for metal nitride-based symmetric SCs is limited (0.6-0.8 V) in aqueous electrolyte due to the oxidation at high negative potentials. In this respect, ultra-small tungsten nitride particles onto the phosphorous modified carbon fabric (W2 N@P-CF) are engineered as a promising hybrid electrode for pseudocapacitors. Additionally, the fact that the W2 N@P-CF electrode can operate in the negative potential region is exploited to design asymmetric pseudocapacitors by coupling with a polypyrrole on carbon fabric (PPy@CF) as the positive electrode. Remarkably, the W2 N@P-CF//PPy@CF asymmetric cell can be cycled in a wide voltage window of 1.6 V that is almost two times higher than that of metal nitrides symmetric SCs. The pseudocapacitive behavior with matching different potential regions of W2 N@P-CF and PPy@CF, considerably enhance performance of asymmetric device. The device delivers high volumetric capacity (7.1 F cm-3 ), high energy (2.54 mWh cm-3 ), power densities, and good cycling stability (88%) over 20 000 cycles. Thus, pseudocapacitive metal nitride-based devices hold a great promise to provide high voltage and improved energy density in aqueous electrolyte.