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.