Role of Water in Electrochemical Urea Oxidation Revealed by Mechanistic Insight in MeCN–H 2 O Mixed Solvents

Urea electrolysis in water is an attractive approach for ultrapure water production; however, the mechanism of electrochemical urea oxidation reaction (UOR) remains unclear. Here, we investigated UOR in MeCN–H 2 O mixed solution by changing the water ratio to reveal the role of water via hydrogen bonding with urea, gaining a mechanistic insight into UOR. The effect of water on UOR was evaluated and argued based on the analysis using 1 H NMR spectroscopy and electrochemical measurements. The results indicated that water molecules can weakly interact with urea (binding constant ( K ) is 0.18 M −1 ), which affect the current on differential pulse voltammetry (DPV). However, the electrochemical urea decomposition rate exhibited a maximum value at 1% water fraction in the range of 0%–30% water contents because the oxidation potential of urea showed a positive shift at higher water fraction. Then, nitrogen‐containing products (NH 4 + , NO 2 − , NO 3 − , and N 2 ) derived from electrochemical UOR were characterized by GC and HPLC in the range of 0%–30% water contents. Judging from these results, we have concluded that the reactivity of electrochemical UOR is dependent on the water fraction and the mechanism of electrochemical UOR is influenced by water due to the hydrogen bonding with urea.