NH- and CH-Substituted Ureas as Self-Assembly Directing Motifs for Facile Synthesis and Electrocapacitive Applications of Advanced WO_3–x One-Dimensional Nanorods

Designing a solid state crystal architecture at nanoscale, using a soft chemistry approach, is the key step toward their scalable synthesis for sustainable application in electrochemical charge storage devices. We investigate the application of NH- and CH-substituted ureas, namely, carbohydrazide, semicarbazide, N-methylurea, and tetramethylurea as design elements/motifs in the tailored synthesis of WO3–x nanostructures via direct calcination of tungstic acid-substituted urea hybrid gels. The SEM, HRTEM, SAED, XRD, XPS, and TG-DTA studies reveal that NH-substitution in urea induces a profound growth of WO3–x one-dimensional (1D) nanorods, preferentially growing along the (002) plane with enhancement in the percentage of oxygen vacancies. On the contrary, with the increase in CH-substitution in urea, the tendency to form 1D nanorods via self- assembly process decreases, possibly due to an increase in the steric effect of the methyl groups. We further demonstrate the corresponding effect of morphological and chemical changes in WO3–x nanostructure on their improved electrified interfacial processes via H+ intercalation using cyclic voltammetry, galvanostatic charge–discharge, electrochemical impedance spectroscopy tests, and chronoamperometric studies. Our findings reveal that the enhancement in WO3–x nanorod growth, W5+/W6+ redox surface states, and abundance of (002) surface plane due to NH-substitution in urea play a crucial role in facilitating the diffusion process of H+/e– in and out of the WO3–x matrix. An area specific capacitance of 132 mF cm–2 at the current density of 1 mA cm–2 with excellent capacitance retention is reported. Moreover, significant improvements in the charge–discharge times were observed, the highest being the one for WO3–x nanorods obtained using carbohydrazide, demonstrating its potential for possible application in designing 1D nanomaterials for energy storage systems.