Selective Electrocatalytic Oxidation of Nitrogen to Nitric Acid Using Manganese Phthalocyanine

Abstract

Ammonia is produced through the energy-intensive Haber–Bosch process, which undergoes catalytic oxidation for the production of commercial nitric acid by the senescent Ostwald process. The two energy-intensive industrial processes demand for process sustainability. Hence, single-step electrocatalysis offers a promising approach toward a more environmentally friendly solution. Herein, we report a 10-electron pathway associated one-step electrochemical dinitrogen oxidation reaction (N 2 OR) to nitric acid by manganese phthalocyanine (MnPc) hollow nano-structures under ambient conditions. The catalyst delivers a nitric acid yield of 513.2 μmol h –1 g cat –1 with 33.9% Faradaic efficiency @ 2.1 V versus reversible hydrogen electrode. The excellent N 2 OR performances are achieved due to the specific-selectivity, presence of greater number of exposed active sites, recyclability, and long period stability. The extended X-ray absorption fine structure confirms that Mn atoms are coordinated to the pyrrolic and pyridinic nitrogen via Mn–N 4 coordination. Density functional theory-based theoretical calculations confirm that the Mn–N 4 site of MnPc is the main active center for N 2 OR, which suppresses the oxygen evolution reaction. This work provides a new arena about the successful example of one step nitric acid production utilizing a Mn–N 4 active site-based metal phthalocyanine electrocatalyst by dinitrogen oxidation for the development of a carbon-neutral sustainable society.