NH- and CH- substituted ureas as self-assembly directing motifs for facile synthesis and electrocapacitive applications of advanced WO sub(3-x) 1D nanorods

Abstract

Designing a solid state crystal architecture at nanoscale using soft chemistry approach, is the key step towards 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 WO sub(3-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 WO sub(3-x) 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 WO sub(3-x) nanostructure on their improved electrified interfacial processes via H sup(+) intercalation using cyclic voltammetry, galvanostatic charge - discharge, electrochemical impedance spectroscopy tests and chronoamperometric studies. Our findings reveal that the enhancement in WO sub(3-x) nanorod growth, W sup(5+)/W sup(6+) redox surface states and abundance of (002) surface plane due to NH-substitution in urea, plays a crucial role in facilitating the diffusion process of H sup(+)/e sup(-) in and out of the WO sub(3-x) matrix. An area specific capacitance of 132 mF cm sup(-2) at the current density of 1 mA cm sup(-2) with excellent capacitance retention is reported. Moreover, significant improvement in the charge discharge times were observed, highest being the one for WO sub(3-x) nanorods obtained using carbohydrazide, demonstrating its potential for possible application in designing 1D nanomaterials for energy storage systems.