A New Facile Synthesis of Tungsten Oxide from Tungsten Disulfide: Structure Dependent Supercapacitor and Negative Differential Resistance Properties.

Tungsten oxide (WO3 ) is an emerging 2D nanomaterial possessing unique physicochemical properties extending a wide spectrum of novel applications which are limited due to lack of efficient synthesis of high-quality WO3 . Here, a facile new synthetic method of forming WO3 from tungsten sulfide, WS2 is reported. Spectroscopic, microscopic, and X-ray studies indicate formation of flower like aggregated nanosized WO3 plates of highly crystalline cubic phase via intermediate orthorhombic tungstite, WO3. H2 O phase. The charge storage ability of WO3 is extremely high (508 F g-1 at current density of 1 A g-1 ) at negative potential range compared to tungstite (194 F g-1 at 1 A g-1 ). Moreover, high (97%) capacity retention after 1000 cycles and capacitive charge storage nature of WO3 electrode suggest its supremacy as a negative electrode of supercapacitors. The asymmetric supercapacitor, based on the WO3 as a negative electrode and mildly reduced graphene oxide as a positive electrode, manifests high energy density of 218.3 mWhm-2 at power density 1750 mWm-2 , and exceptionally high power density, 17 500 mW m-2 , with energy density of 121.5 mWh m-2 . Furthermore, the negative differential resistance (NDR) property of both WO3 and WO3 .H2 O are reported for the first time and NDR is explained with density of state approach.