Solvent‐in‐Gas System for Promoted Photocatalytic Ammonia Synthesis on Porous Framework Materials

Abstract

Photocatalytic nitrogen reduction reaction (PNRR) is emerging as a sustainable ammonia synthesis approach to meet global carbon neutrality. Porous framework materials with well‐designed structures have great opportunities in PNRR; however, they suffer from unsatisfactory activity in the conventional gas‐in‐solvent system (GIS), owing to the hindrance of nitrogen utilization and strong competing hydrogen evolution caused by overwhelming solvent. In this study, porous framework materials are combined with a novel “solvent‐in‐gas” system, which can bring their superiority into full play. This system enables photocatalysts to directly operate in a gas‐dominated environment with a limited proton source uniformly suspended in it, achieving the accumulation of high‐concentrated nitrogen within porous framework while efficiently restricting the solvent‐photocatalyst contact. An over eightfold increase in ammonia production rate (1820.7 µmol g−1 h−1) compared with the conventional GIS and an apparent quantum efficiency as high as ≈0.5% at 400 nm are achieved. This system‐level strategy further finds applicability in photocatalytic CO2 reduction, featuring it as a staple for photosynthetic methodology.

In Situ Construction of Metal–Organic Frameworks as Smart Channels for the Effective Electrocatalytic Reduction of Nitrate at Ultralow Concentrations to Ammonia

“…The possible intermediates or products adsorbed on the electrode surface were characterized by in situ FTIR spectroscopy under different applied potentials from 0 to −1.4 V (vs RHE) . As illustrated in Figure c, the band observed at 1650 cm –1 is due to the O–H bending of H 2 O, and the broad band at about 3300 cm –1 is associated with the O–H stretching vibration of interfacial H 2 O in the sulfate electrolyte . The band located at about 3600 cm –1 is the N–H stretching vibration, which is responsible for ammonia formation during the electrocatalytic nitrate reduction reaction process.…”

“…33 As illustrated in Figure 4c, the band observed at 1650 cm −1 is due to the O−H bending of H 2 O, and the broad band at about 3300 cm −1 is associated with the O−H stretching vibration of interfacial H 2 O in the sulfate electrolyte. 9 The band located at about 3600 cm −1 is the N−H stretching vibration, which is responsible for ammonia formation during the electrocatalytic nitrate reduction reaction process. The negative bond of nitrate (∼1382 cm −1 ) is observed when the potential reaches −0.6 V (vs RHE), while no bands associated with possible intermediates are observed because of the excess nitrate and low coverage of nitrate reduction intermediates.…”

“…It is increasingly critical to remove nitrates from water and subsequently convert them into harmless or, better yet, high-value-added products. Electrocatalytic reduction driven by renewable electricity has emerged as an effective strategy to manage nitrates in water, during which nitrogen oxyanions, hydroxylamine, dinitrogen, and ammonia are the main products. , Particularly, ammonia (NH 3 ) is the cornerstone for agricultural fertilizer and industrial chemical manufacture and also an important energy storage medium and carbon-free energy carrier. − Industrial-scale NH 3 production heavily relies on the energy-intensive Haber–Bosch process, which requires harsh operating conditions (including high temperature and pressure) and consumes significant amounts of energy. − As an alternative, the electrocatalytic dinitrogen (N 2 ) reduction reaction (NRR) in water under ambient conditions has attracted increasing attention for its safety, low cost, and environmental friendliness. , However, the reaction rate and selectivity are hampered by the extremely stable NN triple bond (941 kJ mol –1 ) in nonpolar N 2 gas. , Ideally, NO 3 – is considered as an attractive nitrogen source because of the relatively low dissociation energy of the NO bond (204 kJ mol –1 ). Simultaneously, it is one of the most widespread water pollutants in the world, which seriously endangers human health and the ecological environment .…”

Green and large‐scale production of ammonia: Laser‐driven pyrolysis of nitrogen‐enriched biomass

“…As is well‐known, various technical routes, such as thermocatalysis and photocatalysis, were employed to achieve efficient ammonia synthesis. From a comprehensive perspective in Figure 4F, the ammonia production of 260.4 mg/h by laser‐driven pyrolysis outperformed an order of magnitude than previous results, such as thermocatalysis (catalyst: Ni/CeN, NH 3 yield: 11.05 mg/h), photocatalysis (catalyst: F‐Vo‐TiO 2 , NH 3 yield: 1.75 mg/h) 35–42 . In addition, laser‐driven pyrolysis only needed a 20 W pulse laser, which consumed one to two orders of magnitude less energy (2.4 ⨯ 10 11 J/mt NH3 ) than the reported ammonia synthesis methods (Figure 4G).…”

“…From a comprehensive perspective in Figure 4F, the ammonia production of 260.4 mg/h by laser-driven pyrolysis outperformed an order of magnitude than previous results, such as thermocatalysis (catalyst: Ni/CeN, NH 3 yield: 11.05 mg/h), photocatalysis (catalyst: F-Vo-TiO 2 , NH 3 yield: 1.75 mg/h). [35][36][37][38][39][40][41][42] In addition, laser-driven pyrolysis only needed a 20 W pulse laser, which consumed one to two orders of magnitude less energy (2.4 ⨯ 10 11 J/mt NH3 ) than the reported ammonia synthesis methods (Figure 4G). 37,[43][44][45] Most importantly, the laser-driven pyrolysis of biomass for ammonia synthesis effectively utilized the green and renewable sources of hydrogen and nitrogen, avoiding the consumption of high-value H 2 .…”