Porous molybdenum tungsten oxynitrides enable long-life supercapacitors with high capacitance

Abstract

Binary transition metal oxides with multiple active sites are considered as one of the most potential anode candidates for high-performance supercapacitors (SCs) but their inferior conductivity is utterly disappointing. Herein, a molybdenum tungsten oxynitride with a porous architecture is designed and synthesized by nitriding its bimetallic oxide counterpart under ammonia atmosphere. The ingenious introduction of nitrogen atoms into the binary oxide not only leads to an enlarged specific surface area with complete hydrophilicity, but also results in an optimized electrical conductivity, which synergistically strengthen its supercapacitive properties. As a proof of concept, the oxynitride electrode displays a remarkable areal capacitance of 2.43 F cm−2 at 4 mA cm−2 and exhibits high cycling stability (no noticeable decay after 20,000 cycles), considerably superior to that of the pristine sample. A high-performance aqueous asymmetric SC with long lifespan is also achieved by coupling the oxynitride anode with a MnO2 cathode. Specifically, the device delivers an energy density of 1.67 mW h cm−3 and holds a power density of 0.23 W cm−3, outstripping plenty of recently reported asymmetric SCs. This work provides a new train of thought for boosting the performance of energy storage systems based on binary transition metal oxides.