Direct evidence of the mechanism for the electro-oxidation of urea on Ni(OH)2 catalyst in alkaline medium

The electrochemical oxidation mechanism of urea on a Ni(OH)2 catalyst in alkaline medium was investigated using in situ surface enhanced Raman spectroscopy. It was demonstrated that the urea oxidation follows a catalyst regeneration mechanism. In the proposed mechanism, Ni(OH)2 is electrochemically oxidized to NiOOH that mediates the urea oxidation reaction. During the urea oxidation process, the catalytically active NiOOH is chemically reduced to the inactive Ni(OH)2 by urea, concurrently, urea is chemically oxidized to its products. The inactive Ni(OH)2 is electrochemically oxidized to NiOOH due to the prevailing high oxidation potential thus regenerating the catalyst for further oxidation of urea molecules.