Facile Preparation of Carbon Shells-Coated O-Doped Molybdenum Carbide Nanoparticles as High Selective Electrocatalysts for Nitrogen Reduction Reaction under Ambient Conditions

Abstract

Electrochemical nitrogen reduction reaction (NRR) has been considered as a promising alternative to the traditional Haber–Bosch process for the preparation of ammonia (NH3) under ambient conditions. The development of cost-effective electrocatalysts with suppressive activity for hydrogen evolution reaction is critical for improving the efficiency of NRR. Herein, oxygen-containing molybdenum carbides (O-MoC) embedded in nitrogen-doped carbon layers (N-doped carbon) can be easily fabricated by pyrolyzing the chelate of dopamine and molybdate. A rate of NH3 formation of 22.5 μg·h–1·mgcat –1 is obtained at −0.35 V versus reversible hydrogen electrode with a high faradaic efficiency of 25.1% in 0.1 mM HCl + 0.5 M Li2SO4. Notably, the synthesized O-MoC@NC-800 also exhibits high selectivity (no formation of hydrazine) and electrochemical stability. The moderate electron structure induced by the interaction between O-MoC and N-doped carbon shells can effectively weaken the activity of hydrogen evolution reaction and increase the faradaic efficiency of NRR. Additionally, by applying the in situ Fourier transform infrared spectroscopy, an associative reaction pathway is proposed on O-MoC@NC-800. This work provides new insights into the rational design of carbon-encapsulated metal nanoparticles as efficient catalysts for NRR at ambient conditions.

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

“…Interestingly, it displayed better performance by delivering 8.13% efficiency with 95.1 µg h −1 mg cat yield rate at −0.3 V. [88] Recently, Sun et al came up with innovative carbon shells-coated O-doped Mo 2 C NPs embedded in N doped carbon layers (O-MoC@NC) to optimize the electrocatalytic activity of Mo 2 C for NRR. O-MoC@NC manifested high efficiency (25.1%) with yield rate of 22.5 µg h −1 mg cat −1 at −0.35 V. [89] Its noteworthy to note that 0.1 × 10 −3 m HCl + 0.5 m LiSO 4 electrolyte has been adopted in this work. The outstanding activity was assigned to enhanced electron transfer between Mo 2 C and N-doped carbon sheets.…”

Recent Advances in Electrochemical Synthesis of Ammonia through Nitrogen Reduction under Ambient Conditions

“…Therefore, the associative distal pathway theoretically has higher product selectivity because it is a continuous six‐electron reaction process without a partial four‐electron step. However, this does not mean that N 2 H 4 must be produced through the mechanism of alternating hydrogenation; through research of the NRR catalyst library, there are many materials showing excellent selectivity without N 2 H 4 production, such as Nb 2 O 5 and O−MoC at NC . This phenomenon may be caused by the reaction process following a six‐electron approach instead of generating N 2 H 4 through four electron transfer as the feeble second and third bonds of N 2 make hydrogenation simple.…”

“…Sun et al. prepared oxygen‐doped molybdenum carbides (O−MoC) embedded in nitrogen‐doped carbon layers (O−MoC@NC) via pyrolyzing the chelate of dopamine and molybdate . As shown in Figure , SEM and TEM show the flake morphology and core‐shell structure of O−MoC@NC.…”

“…The author employed in‐situ FTIR to probe the NRR course on O−MoC@NC. With the appearance of H−N−H bending, −NH 2 wagging and N−N stretching in the in‐situ FTIR spectra, the process of the may follow the alternating pathway . Although some excellent transition metal catalysts have been developed by designing the distribution and structures of active sites, the HER side reaction in the reaction system still dominates.…”

“…reported the use of a simple method to introduce oxygen vacancies to improve nitrogen reduction. It is reported that the oxygen vacancy provides a rich Lewis base for R−BiOI, thus improving the adsorption and activation ability of nitrogen . Moreover, defect engineering and heteroatom doping strategies can also provide new insights into improving nitrogen reduction reaction by overcoming the kinetic limitations of nitrogen reduction to increase the selectivity of the catalyst to nitrogen.…”