Morphology and crystal structure dependent pseudocapacitor performance of hydrated WO3 nanostructures

Abstract

The strategic morphology tuning of hydrated WO₃ nanostructures from two-dimensional (2D) nanosheets to three-dimensional (3D) slabs with enhanced in-plane crystalline nature and multilayered construction is realized via tailoring the synthesis temperature. The increasing synthesis temperature expands the degree of crystallinity, specific surface area and thickness of layered WO₃·H₂O sheets which results in slab like 3D morphology as characterized by X-ray diffraction spectra (XRD), Raman spectra and scanning electron microscopy (SEM). The electrochemical study reveals the higher specific capacitance (386 F g⁻¹) of 3D slabs compared to that of 2D nanosheets (254 F g⁻¹) at a scan rate of 2 mV s⁻¹. Moreover, 3D slabs demonstrate an excellent capacitance retention of 96% compared to 2D nanosheets (86%) after 3000 cycles. The enhanced performance of supercapacitors in 3D slabs is attributed to three significant aspects: first, confined coordinated hydrate in the crystalline layer provides a significant surface area and allows fast electrochemical proton insertion via the Eigen–Zundel–Eigen mechanism; second, the enhanced crystalline nature offers improved in-plane conductivity; and finally the structural defects and disorders due to the layered structure promote faradaic redox reactions.