Synthesis of 1D WO3 nanostructures using different capping agents for pseudocapacitor applications.

To investigate the correlation between electrochemical performance and physicochemical properties, three types of 1D WO3 nanostructures were fabricated by hydrothermal method using K2SO4, Na2SO4, and (NH4)2SO4 as capping agents. Hexagonal phase was obtained with the assistant of Na2SO4 and (NH4)2SO4, while monoclinic phase was developed using K2SO4 as agent. WO3 nanostructures prepared by (NH4)2SO4 and Na2SO4 exhibited superior specific capacitance (400 F/g and 388 F/g) relative to WO3 prepared by K2SO4 (259 F/g), suggesting hexagonal phase is more suitable for energy storage. The nanostructures prepared using Na2SO4 exhibited inferior rate performance compared with those obtained by (NH4)2SO4 due to low specific surface area and high crystallinity. The electrochemical performance demonstrated nanostructures prepared by (NH4)2SO4 was surface-controlled whereas those using Na2SO4 and K2SO4 were battery-type material. These findings raise the prospects of developing tungsten oxide for energy storage. [ABSTRACT FROM AUTHOR]