NICKEL COMPLEXES AS POTENTIAL CATALYSTS FOR UREA CONVERSION

In order to meet the growing global demands for energy in the age of environmental awareness, alternative clean energy sources must be explored. Hydrogen gas is such a source of energy, with water being the only byproduct in its energy conversion process. Urea electrolysis is a promising new technology that has the capacity to produce high-purity hydrogen from sustainable sources, such as wastewater. Urea is a highly attractive hydrogen carrier, because it is abundant, stable, non-toxic and non-flammable, and can be stored and transported conveniently, since it is solid under ambient conditions.

Nickel metal and nickel oxides have been studied extensively as electrocatalysts for urea conversion, providing relatively high current densities and low overpotentials of oxidation to CO₂ and N₂. Moreover, nickel is intimately involved in urea hydrolysis within the active site of the enzyme urease, and this has inspired chemists to mimic the naturally-occurring bimetallic core of this enzyme. Simplified synthetic bimetallic model systems have been studied as part of the effort to probe the enzymatic mechanism, as well as examine other reactivity patterns.

To the best of our knowledge, no molecular nickel-based system has thus far been reported to promote the electrochemical conversion of urea. Herein, we present the synthesis and characterization of nickel complexes of phenol-based binucleating ligands. These are intended to mimic the active nickel-oxide surfaces previously shown to promote urea conversion, with the aim of developing catalysts for urea electrooxidation.