Electrocatalytic N₂ Fixation over Hollow VO₂ Microspheres at Ambient Conditions

Abstract

Electrochemical N 2 fixation has gained much attention as an environmentally friendly and sustainable process for NH 3 production at ambient conditions. Its efficiency depends greatly on identifying highly active electrocatalysts with good stability. In this work, we propose the use of VO 2 hollow microspheres as a robust non-precious metal catalyst for the N 2 reduction reaction (NRR). The catalyst operates efficiently and stably at neutral pH to high Faradaic efficiency (3.97 %) and NH 3 yield (14.85 μg h À 1 mg À 1 cat. ) under an applied potential of À 0.7 V (vs. the reversible hydrogen electrode). Note that this catalyst also presents a high selectivity for NH 3 synthesis without N 2 H 4 generation. Density functional theory reveals that the energetically favorable pathway for NRR is *N 2 !*NNH!*NHNH! *NHNH 2 !*NH 2 NH 2 !*NH 2 + NH 3 !*NH 3 + NH 3 !2NH 3 , where the first hydrogenation step to form *NNH is the potentialdetermining step. NH 3 is not only a vital chemical for the manufacture of agricultural and industrial products, but an attractive liquid fuel and a high-efficiency energy carrier (hydrogen content of 17.8 wt %). [1][2][3] The most abundant molecular N 2 , making up 78 % of the atmosphere, is so chemical inert that it does not engage in most chemical reactions, making artificial N 2 fixation a challenging task. [4] Industrially, N 2 reduction to NH 3 is performed by traditional Haber-Bosch process over an enriched Fe-or Ru-based catalyst at high temperature and pressure (350-550°C, 150-350 bar). [5,6] This process accounts for more than 1 % of the world's annual energy consumption. [7,8] Another concern with this process is that the production of H 2 from fossil fuels emits a large amount of greenhouse gas. [9] In this context, we need to explore more sustainable and greener approach to produce NH 3 .The electrochemical reduction of N 2 using water as a proton source is a particularly promising means to achieve this aim since it can operate at room temperature and atmospheric pressure powered by electricity produced from wind, solar or nuclear energy. [10][11][12] However, it needs active, selective and stable materials to catalyze the N 2 reduction reaction (NRR) and the catalysts play a significant role in NH 3 yield, efficiency, and production cost. A variety of noble metal-based NRR electrocatalysts have been investigated for NH 3 production at ambient conditions. [13][14][15][16] However, they are low-abundance and expensive, which limit the wide uses, inspiring the search for costeffective alternatives. So far, several studies have focused on utilizing earth-abundant materials to perform NRR. [17][18][19][20][21][22][23][24][25] Although progress has been achieved in this respect, identifying new such catalysts is still in great need.V plays a vital role in nitrogenases to catalyze biological N 2 fixation under mild conditions, [26] and its complexes have been designed and developed for N 2 reduction. [27] In this regard, it is quite interesting to investigate the electrochemical behavi...

CuO/Graphene Nanocomposite for Nitrogen Reduction Reaction

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Greatly Enhanced Electrocatalytic N2 Reduction over V2O3/C by P Doping

“…Our early study suggests that the VO 2 hollow microsphere is active for the NRR with an NH 3 yield of 14.85 μg h −1 mg −1 cat. and a Faradaic efficiency (FE) of 3.97% at −0.7 V vs. reversible hydrogen electrode (RHE) . To overcome the issue of intrinsically low electrical conductivity of V 2 O 3 with less toxicity, we developed V 2 O 3 /C shuttle‐like nanostructure from metal‐organic framework for N 2 reduction electrocatalysis, but further work still needs to enhance the NRR performances of such catalyst.…”

Structured Polyaniline: An Efficient and Durable Electrocatalyst for the Nitrogen Reduction Reaction in Acidic Media

“…Noble metal (Au, Ru, Rh, Ag, etc)‐based NRR catalysts show excellent activity, whereas the high cost limits their widespread utilizations. Therefore, exploration of non‐noble‐metal alternatives has gained much attention . Contrasted with above catalysts, metal‐free materials have a distinct advantages in avoiding metal ion release, which could reduce the environmental impact .…”