Mechanistic Insights into the Stabilization of In Situ Formed γ-NiOOH Species on Ni60Nb40 Nanoglass for Effective Urea Electro-Oxidation

The formation of NiOOH on the catalyst surface is widely considered to be the active species in electrochemical urea oxidation reactions (UOR). Though in situ-formed NiOOH species are reported to be more active than the synthesized ones, the mechanistic study of the actual active species remains a daunting task due to the possibility of different phases and instability of surface-formed NiOOH. Herein, mechanistic UOR aspects of electrochemically activated metallic Ni60Nb40 Nanoglass showing stability toward the gamma-NiOOH phase are reported, probed via in situ Raman spectroscopy, supported by electron microscopy analysis and X-ray photoelectron spectroscopy in contrast with the beta-NiOOH formation favored on Ni foil. Detailed mechanistic study further reveals that gamma-NiOOH predominantly follows a direct UOR mechanism while beta-NiOOH favors indirect UOR from time-dependent Raman study, and electrochemical impedance spectroscopy (EIS) analysis. The Nanoglass has shown outstanding UOR performance with a low Tafel slope of 16 mV dec(-1) and stability for prolonged electrolysis (approximate to 38 mA cm(-2) for 70 h) that can be attributed to the nanostructured glassy interfaces facilitating more gamma-NiOOH species formation and stabilization on the surface. The present study opens up a new direction for the development of inexpensive Ni-based UOR catalysts and sheds light on the UOR mechanism.