pH-Dependent Electrocatalytic Aqueous Ammonia Oxidation to Nitrite and Nitrate by a Copper(II) Complex with an Oxidation-Resistant Ligand
Hanyu Liu, Hannah M. C. Lant, Cristina Decavoli, Robert H. Crabtree, Gary W. Brudvig
Abstract
The electrocatalytic aqueous ammonia oxidation (AO) represents a more sustainable alternative to accessing nitrite (NO 2 – ) and nitrate (NO 3 – ). We now report that Cu(pyalk) 2 {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 2 – /NO 3 – was modified to permit the operation in the presence of the otherwise interfering Cu 2+ ion. Choosing the right pH is crucial for achieving high AO selectivity, with optimal formation of NO 2 – 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.