Comparing the mechanism of urea and ammonia electro-oxidation reactions on Ni-based catalysts
Résumé
In recent decades, special attention has been paid to the electrochemical oxidation of organic
compounds, such as urea (H2NCONH2) from urine, in order to avoid their natural degradation into
detrimental products, as well as to produce energy by using fuel cells [1]. Its presence in sewages and
its natural decomposition into ammonia (NH3) can adversely affect our environment. Urea is naturally
decomposed into ammonia by the enzyme urease, therefore, the electro-oxidation of both compounds
must be addressed as concomitant reactions, and requires a comparative study. Nickel-based materials
have received attention for both urea and ammonia electro-oxidations due to their low cost, high
abundance, and high activity in alkaline solutions. However, it has been suggested that urea follows
an indirect pathway involving a chemical reaction with NiOOH (EC’ mechanism), different to
ammonia, in which case it follows a direct electrochemical pathway (E mechanism) [2].
This work aims to compare the mechanism of urea and ammonia electro-oxidation reactions on Nibased
nanocatalysts (Ni and NiO) as a function of applied potential under controlled mass transport
conditions. Hence, rotating disk electrode (RDE), cyclic voltammetry, electrochemical impedance
spectroscopy (EIS), and chronoamperommetry results are presented (fig.1). The effect of urea electrooxidation
byproducts such as cyanate, ammonia, nitrite, and carbonate, the impact of the supporting
electrolyte and urea concentrations, as well as the effect of ions and other molecules present in
samples of artificial human urine such as Cl- and creatinine have been successfully studied herein.