Influences of tungsten incorporation, morphology and calcination temperature on the electrocatalytic activity of Ni/C nanostructures toward urea elimination from wastewaters

Abstract

Electrooxidation of urea is an efficient methodology for the production of hydrogen with a simultaneous treatment of urea-containing wastewaters. In this study, tungsten was suggested as a co-catalyst to foster the activity of Ni/C nanostructures in the process of urea electro-oxidation. Beside optimization of the co-catalyst content, influences of the nano-morphology and the synthesis temperature have been investigated. The results indicated that WNi nanoparticles-incorporated carbon nanofibers can be produced from calcination of electrospun mats composed of nickel acetate, tungsten chloride, and ploy (vinyl alcohol). Compared to the nanoparticles, the morphology of nanofibrous was strongly foster the electrocatalytic activity. The W-free and the prepared, from calcination of an electrospun solution containing 10 wt% WCl2 at 850 °C, nanofibers give better performance compared to the nanoparticles having similar compositions. Compared to the nanoparticles, the nanofibrous morphology results in increasing the current density from 11.5 to 16 mA/cm2 (28% increase) and from 22 to 37.75 mA/cm2 (42% increase) for the pristine and W- containing catalyst, respectively. Studying the influence of the metallic nanoparticles composition indicated that the tungsten content strongly affects the electrocatalytic activity; the nanofibers prepared from electrospun solution containing 35 wt% tungsten precursor reveal the best performance. Investigating the effect of the calcination temperature indicated that 1000 °C is the optimum temperature compared to 700 and 850 °C. Numerically, for 10 wt% co-catalyst sample, the current density was duplicated four times when the calcination temperature increased from 850 to 1000 °C. Studying the kinetic of urea oxidation reaction concluded that the activation energy is ~17 kJ/mol.