Selecting between Ammonia and Water Oxidation: Electrochemical Oxidation of Ammonia in Water Using an Organometallic–Inorganic Hybrid Anode

Abstract

Electrocatalytic ammonia oxidation (AO) under ambient conditions in an aqueous solvent enables an ecofriendly production of nitrite and nitrate. Conventional formation of nitrite and nitrate by AO on noble metals often yields undesired dinitrogen and leads to detrimental nitride surface poisoning. We now find that our previously reported “Blue Layer” (BL), an organometallic–inorganic hybrid anode based on [IrO2] x nanoclusters (x ∼ 5), is active for selective AO in aqueous solution. Through adjustment of both pH and applied potential (E app), we identified optimal operating conditions (pH 8.0, 1.00 V) for AO, where BL achieves optimum selectivity toward nitrate (90.5%), effectively minimizing competitive water oxidation while maintaining activity against ammonia-induced degradation of the electrode.

Cooperative oxidation of NH3 and H2O to selectively produce nitrate via a nearly barrierless N–O coupling pathway

“…Nitrite (NO 2 − ) or nitrate (NO 3 − ) (denoted as NO x − ) is an essential bulk chemical widely utilized in various applications, such as fertilizers, feedstocks, pharmaceuticals, etc. 1,2 NO x − is mainly produced industrially by Ostwald ammonia (NH 3 ) oxidation, which is the second-largest nitrogen-based process worldwide. 3–5 The whole process is strongly exothermic with an energy release of −905.2 kJ mol −1 during NO production [4NH 3 (g) + 5O 2 (g) = 4NO(g) + 6H 2 O(g)].…”