Evidence for Exclusive Direct Mechanism of Urea Electro-Oxidation Driven by In Situ-Generated Resilient Active Species on a Rare-Earth Nickelate

Stabilization of active NiOOH species for achieving exclusive operation of the direct mechanism of the urea electro-oxidation reaction (UOR) presents a formidable challenge. Despite the extensive repertoire of UOR electrocatalysts developed so far, the sustenance of active NiOOH species throughout the reaction remains unaccomplished due to the predominant operation of the indirect mechanism that involves the reduction of NiOOH into Ni(OH)2 during electrocatalysis. The capability of a UOR electrocatalyst to retain the active species is of paramount importance as it ensures the optimal engagement of the maximum pool of active Ni centers in the electrocatalytic process, resulting in enhanced activity with reduced Ni mass loading. In this context, the present study unveils the electrocatalytic UOR capability of a rare-earth nickelate, NdNiO3, showcasing high UOR activity with a reduced burden of Ni mass loading. From the detailed cyclic voltammetry studies, in situ X-ray absorption spectroscopy, and impedance analyses, it has been substantiated that NdNiO3 triggers the UOR to proceed through the unconventional direct mechanism, obviating the need for catalyst regeneration during UOR. The adsorption free energy calculation of reactants such as urea, OH– ions, and product CO2 reveals that NdNiO3 effectively interacts with the reactants, and its surface is highly tolerant toward COx poison when compared to NiO. The preferential direct mechanism of UOR, enhanced mass activity, and commendable resistance against COx poisons emanate from the more facile formation and effective stabilization of active NiOOH species on NdNiO3.