Journal
JOURNAL OF MATERIALS CHEMISTRY A
Volume 7, Issue 28, Pages 16969-16978Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c9ta05155d
Keywords
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Funding
- Natural Science Foundation of China [51602315, 51672277, 61804154]
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Deeply understanding the electrochemical activation and inactivation processes of an electrocatalyst is critically important for establishing a high-efficiency nitrogen reduction reaction (NRR) to synthesize an NH3 system. Here we report the utilization of a facile vapor-phase hydrothermal (VPH) method to directly grow ultrafine Nb3O7(OH) nanoparticles on commercial carbon fiber cloth (Nb3O7(OH)/CFC) for the NRR. The results demonstrate that the Nb3O7(OH)/CFC can afford an average NH3 yield rate of 622 mu g h(-1) mg(cat.)(-1) with a high faradaic efficiency (FE) of 39.9% at -0.4 V versus the reversible hydrogen electrode (RHE) in 0.1 M Na2SO4 electrolyte (pH = 6.1) within 30 min of the NRR, surpassing the performance of most recently reported aqueous-based NRR electrocatalysts. The experimental and theoretical calculation results reveal that the in situ electrochemically converted NbO from Nb3O7(OH) during the NRR is the catalytic active phase with a N-2 adsorption free energy of -0.97 eV; however with a reaction time over 30 min, the generated active *N atoms in the *N-NH3 -> *N + NH3 hydrogenation step during the NRR are thermodynamically favourable for binding to the oxygen vacancies of NbO to form oxygen-containing NbN0.64 with reduced N-2 adsorption free energy (-0.32 eV), resulting in significantly decreased NRR activity. Our studies suggest that although NbO possesses high NRR activity, it may not be a suitable NRR electrocatalyst, owing to easy formation of low active niobium oxynitride during the NRR.
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