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 WO 3 nanostructures were fabricated by hydrothermal method using K 2 SO 4 , Na 2 SO 4 , and (NH 4 ) 2 SO 4 as capping agents. Hexagonal phase was obtained with the assistant of Na 2 SO 4 and (NH 4 ) 2 SO 4 , while monoclinic phase was developed using K 2 SO 4 as agent. WO 3 nanostructures prepared by (NH 4 ) 2 SO 4 and Na 2 SO 4 exhibited superior specific capacitance (400 F/g and 388 F/g) relative to WO 3 prepared by K 2 SO 4 (259 F/g), suggesting hexagonal phase is more suitable for energy storage. The nanostructures prepared using Na 2 SO 4 exhibited inferior rate performance compared with those obtained by (NH 4 ) 2 SO 4 due to low specific surface area and high crystallinity. The electrochemical performance demonstrated nanostructures prepared by (NH 4 ) 2 SO 4 was surface-controlled whereas those using Na 2 SO 4 and K 2 SO 4 were battery-type material. These findings raise the prospects of developing tungsten oxide for energy storage. Graphical abstract