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 (N2OR) 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 gcat –1 with 33.9% Faradaic efficiency @ 2.1 V versus reversible hydrogen electrode. The excellent N2OR 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–N4 coordination. Density functional theory-based theoretical calculations confirm that the Mn–N4 site of MnPc is the main active center for N2OR, 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–N4 active site-based metal phthalocyanine electrocatalyst by dinitrogen oxidation for the development of a carbon-neutral sustainable society.

Controlling the Metal–Ligand Coordination Environment of Manganese Phthalocyanine in 1D–2D Heterostructure for Enhancing Nitrate Reduction to Ammonia

“…In the XRD pattern, a peak is observed at ∼25 degrees (2 theta), confirming the formation of RGO for the (002) plane. In Figure a, two main diffraction peaks at 2 theta values of 6.91 and 9.12° are indexed to (100) and (1̅02), respectively (card no #02–063–3894), confirming the formation of β–MnPc. , A broad peak at ∼25 degrees (2 theta) was also observed, which indicates the formation of a 1:2 MnPc:RGO system. Different types of chemical bonds present in 1:2 MnPc:RGO were identified by Fourier transform infrared spectroscopy (FTIR) (Figures b and Table S1).…”

“…The in-plane C–N and C–C stretching vibrations were assigned to 1200–1800 cm –1 . The peak at 1078 cm –1 corresponds to the C–N out-of-plane bending vibration in the MnPc:RGO system. , The UV–vis spectra of MnPc and the 1:2 MnPc:RGO electrocatalyst were analyzed in an ethanol medium. The UV–vis spectrum of MnPc:RGO showed (Figure S2) a characteristic B-band (Soret band) in the 353 nm region.…”

High-Entropy Perovskite Oxides as a Family of Electrocatalysts for Efficient and Selective Nitrogen Oxidation

“…52,53 As exhibited in Figures 4g and S13−S14, the consecutive cycling experiment of Ru-HEP catalyst was carried out at 1.9 V (vs RHE), displaying a negligible fluctuation range of FE and NO 3 − yield rates in 15 consecutive cycles, suggesting its good stability. 54,55 XRD and XPS studies were further carried out for the Ru-HEP catalyst after the NOR test (Figures S15−S17), which indicated that the electronic structure and oxygenvacancy-site concentration of Ru-HEP presented negligible change after NOR catalysis, demonstrating that its oxygenvacancy-enriched structure was well maintained. These results confirmed that the increased oxygen-vacancy concentration of Ru-HEP derived from its high-entropy configuration can facilitate the activation and/or dissociation of N 2 , thus improving its NOR performance.…”

Fe(TCNQ)2 nanorod arrays: an efficient electrocatalyst for electrochemical ammonia synthesis via the nitrate reduction reaction

“…1–3 The industrially exemplary Haber-Bosch process, which is energy demanding and produces an extensive amount of greenhouse gases, is the primary method for the large scale industrial production of NH 3 . 4–6 A sustainable, environment-friendly, and energy efficient strategy for NH 3 synthesis is the desperate need of the hour. The production of NH 3 from N 2 via the nitrogen reduction reaction (NRR) has recently attracted an enormous amount of research interest.…”