NbO₂ Electrocatalyst Toward 32% Faradaic Efficiency for N₂ Fixation

Abstract

challenging even on the catalyst surface. [4] Thus, although the thermodynamic potentials of nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) are similar, the kinetic activity of NRR (such as the exchange current density) is several orders of magnitudes lower than that of HER. [5,6] As a consequence, the conversion and selectivity of these NRR electrocatalysts have remained prohibitively low.From a kinetic point of view, the key bottleneck for this electrochemical reaction to proceed should rely on the realization of highly efficient electrocatalysts that can not only process NRR effectively, but also limit the water reduction under this condition. [7] Nonetheless, most of the NRR electrocatalysts reported to date are prone to bind water molecules or protons. Ionic liquids, [8] organic solvents, [9] or solid-state proton conductors under high temperatures [10] have also been used to inhibit the HER and to improve the faradaic efficiency of ammonia production (FE NH3 ) to ≈60%. [8] However, these approaches are even more expensive than the traditional Haber-Bosch reaction and not capable of being implemented for large-scale deployment.Theoretical calculations [11] have proposed that several oxides, including the (110) facets of NbO 2 , ReO 2 , and TaO 2 , are potentially excellent NRR electrocatalysts, due to their reasonably high capability for nitrogen reduction to ammonia while simultaneously suppressing the competing water reduction. As NbO 2 is near the top of the volcano plot of potential determining step for electrochemical NRR against the binding energy of *NNH and it is relatively low cost, NbO 2 is considered to be a promising NRR electrocatalyst. A more recent study reported that Nb 2 O 5 nanofiber can serve as a good NRR electrocatalyst with a high FE NH3 of 9.26%. [12] Nonetheless, such an efficiency is still far from the demand for practical electrochemical ammonia synthesis powered by renewable energy like solar power. [7] In this work, we demonstrate that NbO 2 containing Nb 4+ can act as a highly efficient NRR electrocatalyst for ambient ammonia synthesis. Compared to the Nb 2 O 5 counterpart, NbO 2 exhibits both higher FE and production rate of ammonia in an acidic electrolyte, reaching the highest FE NH3 of 32% at −0.6 V versus reversible hydrogen electrode (RHE) and the highest ammonia yield rate of 11.6 µg h −1 mg cat.−1 at −0.65 V versus RHE. The excellent NRR performance of NbO 2 can be attributed to the The electrocatalytic N 2 reduction reaction (NRR) to produce ammonia is an attractive but highly challenging approach, due to the extreme inertness of N 2 molecules and significantly lower N 2 concentration compared to the surrounding water molecules. Herein, NbO 2 nanoparticles are demonstrated as an efficient NRR electrocatalyst with significantly improved electrochemical performances. Compared to Nb 2 O 5 with a similar crystal structure unit but different linkage, the Nb 4+ cation not only provides empty d-orbitals for strong N 2 adsorption, but also a single d-ele...

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

“…Due to the important role played by Fe‐based and Mo‐based catalysts in biological nitrogen fixation, their electrochemistry has been lucubrated. Sun and co‐workers proved that the Mo−C bond can reduce the difficulty of releasing NH 3 from the Mo surface through DFT calculations . This provides a scheme for ameliorating the NRR performance of transition metal catalysts by introducing non‐metal atoms with strong electronegativity.…”

Recent progress towards mild-condition ammonia synthesis

“…The performance is higher than that obtained using noble metals (Ru/C) as an electrocatalyst under comparable reaction conditions [96] . The author proposed that the specific sites formed at the interface between Fe NPs and CNT was responsible for N 2 activation and subsequent hy- [105] and NbO 2 nanoparticles [106] could serve as good NRR electrocatalysts mainly due to the efficient molecular N 2 adsorption and activation, which is caused by the strong electron transfer between Nb oxide and N 2 molecule. Differing from the approaches mentioned above, Chen et al proposed a Li + incorporation strategy for ammonia electrosynthesis under ambient conditions [107] .…”

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

“…In large‐scale applications, noble metal catalyst ssuffer from cost issue . Encouragingly, in recent years, scientists efforts have been put to search and identify earth‐abundant alternatives . V is involved in dinitrogenase for biological N 2 fixation and V‐based complexes also enable N 2 reduction .…”