In Situ Growth of Nitrogen-Doped Carbon Coated γ-Fe; O; Nanoparticles on Carbon Fabric for Electrochemical N; Fixation

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Abstract

Nitrogen fixation to ammonia (NH3) has attracted intensive attention because NH3 is the critical inorganic fertilizers and energy carrier. Haber-Bosch process, the industrial procedure for NH3 production, is confined to the extreme condition requirements. Hence, it is highly desirable to develop a renewable and environment-friendly route for nitrogen fixation to replace the conventional technology. Electrochemical nitrogen reduction reaction (NRR) is one of the most promising techniques since the electrical energy could be produced by synergy with the fast-growing renewable energy. However, electrochemical NRR approach faces huge challenge in breaking extremely high N≡N bond energy (940.95 kJ mol–1) in dinitrogen molecules. Therefore, the exploration of high-activity electrocatalysts for NRR is on the upswing. Here, we report the fabrication of free-standing 3D hybrid electrode by in situ growth of N-doped carbon coated γ-Fe2O3 nanoparticles supported on carbon fabric (γ-Fe2O3-NC/CF), For the architecture, scanning electron microscope (SEM) shows that the γ-Fe2O3-NPs are evenly distributed on the surface of carbon fabric. The enlarged SEM image and transmission electron microscopy (TEM) image of γ-Fe2O3-NC/CF-700 demonstrate that the γ-Fe2O3-NPs are composed of abundant cross-linked nanoparticles embedded into a thin layer of carbon. The high-resolution transmission electron microscopy (HRTEM) image confirms that the γ-Fe2O3 nanoparticles are well coated by amorphous thin carbon shells with lattice spaces of 0.263 nm and 0.253 nm, corresponding to the (220) and (311) planes of γ-Fe2O3. The elemental mapping images of the γ-Fe2O3-NC/CF-700, illustrating the homogeneously distribution of Fe, O, N, C elements. The level of Fe species in Fe2O3-NC/CF-700 hybrid is about 1.04 wt.% as detected by inductively coupled plasma atom emission spectrometry (ICP–AES) analysis. The XPS survey spectra confirm the existence of C, N, O, and Fe elements in all samples. Raman spectra suggest more surface defects in the γ-Fe2O3-NC/CF-700.

With such a novel structure, the free-standing 3D hybrid electrode with γ-Fe2O3-NC catalyst manifests a high Faradaic efficiency (FE) of 12.28 % and a considerable ammonia yield of 11.7×10–10 mo1 s–1 cm–2. The favorable properties, such as good conductivity, specific core-shell structure, and unique cation vacancies active sites, in the as-developed γ-Fe2O3-NC/CF endow the catalyst with highly activity, efficiency and stability toward catalysis of NRR. It is anticipated that this strategy can be promising to fabricate robust and stable electrocatalysts for large-scale nitrogen fixation under ambient conditions.

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