pH-Dependent Electrocatalytic Aqueous Ammonia Oxidation to Nitrite and Nitrate by a Copper(II) Complex with an Oxidation-Resistant Ligand.

The electrocatalytic aqueous ammonia oxidation (AO) represents a more sustainable alternative to accessing nitrite (NO) and nitrate (NO). We now report that Cu(pyalk) {pyalk = 2-(pyridin-2-yl)propan-2-oate}, previously employed as a homogeneous water oxidation (WO) catalyst, is also active for selective AO in aqueous environments. The traditional Griess analytical test for NO/NO was modified to permit the operation in the presence of the otherwise interfering Cu ion. Choosing the right pH is crucial for achieving high AO selectivity, with optimal formation of NO occurring at pH 9 (faradaic efficiency 62%). Electrochemical analysis reveals a monometallic reaction pathway and offers a plausible explanation for the chemoselectivity: at pH 9, AO is dominant, while at elevated pH 13, WO dominates.