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

Han-Yu Liu; Hannah M C Lant; Cristina Decavoli; Robert H Crabtree; Gary W Brudvig

doi:10.1021/jacs.4c11822

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

J Am Chem Soc. 2025 Jan 5. doi: 10.1021/jacs.4c11822. Online ahead of print.

Authors

Han-Yu Liu^{1

2}, Hannah M C Lant¹, Cristina Decavoli^{1

2}, Robert H Crabtree^{1

2}, Gary W Brudvig^{1

2}

Affiliations

¹ Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States.
² Energy Sciences Institute, Yale University, 810 West Campus Drive, West Haven, Connecticut 06516, United States.

PMID: 39757550
DOI: 10.1021/jacs.4c11822

Abstract

The electrocatalytic aqueous ammonia oxidation (AO) represents a more sustainable alternative to accessing nitrite (NO₂^-) and nitrate (NO₃^-). 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 NO₂^-/NO₃^- was modified to permit the operation in the presence of the otherwise interfering Cu²⁺ ion. Choosing the right pH is crucial for achieving high AO selectivity, with optimal formation of NO₂^- 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.