Selective Electrocatalytic Oxidation of Nitrogen to Nitric Acid Using Manganese Phthalocyanine
Ashadul Adalder, Sourav Paul, Biswajit Ghorai, Samadhan Kapse, Ranjit Thapa, N. Abharana, Uttam Kumar Ghorai
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.