Experimental and theoretical understanding on electrochemical activation and inactivation processes of Nb3O7(OH) for ambient electrosynthesis of NH3
Experimental and theoretical understanding on electrochemical activation and inactivation processes of Nb3O7(OH) for ambient electrosynthesis of NH3
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Nb3O7(OH)用于常温电合成NH3的电化学活化和失活过程的实验和理论理解
DOI：
10.1039/c9ta05155d
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发表时间：
2019
影响因子：
11.9
通讯作者：
Zhao Huijun
中科院分区：
文献类型：
--
作者：
Wu Tianxing;Han Miaomiao;Zhu Xiaoguang;Wang Guozhong;Zhang Yunxia;Zhang Haimin;Zhao Huijun
深入理解电催化剂的电化学活化和失活过程对于建立高效的氮还原反应（NRR）合成NH3体系至关重要。在这里，我们报告了利用一个简单的气相水热（VPH）方法，直接生长超细Nb 3 O 7（OH）纳米粒子的商业碳纤维布（Nb 3 O 7（OH）/CFC）的NRR。结果表明，Nb 3 O 7（OH）/CFC可以提供622 μg h−1 mgcat.−1的平均NH3产率，在-0.4 V时，与0.1 M Na 2SO 4电解质（pH = 6.1）中的可逆氢电极（RHE）相比，NRR 30 min内的法拉第效率（FE）高达39.9%，超过了最近报道的水基NRR电催化剂的性能。实验和理论计算结果表明，NRR过程中由Nb 3 O 7（OH）原位电化学转化的NbO是催化活性相，N2吸附自由能为-0.97eV;然而反应时间超过30分钟，在 *N-NH3 → *N +中生成的活性 *N原子NRR过程中的NH3氢化步骤在热力学上有利于与NbO的氧空位结合，形成具有降低的N2吸附自由能的含氧NbN0.64（-0.32 eV），导致NRR活性显著降低。我们的研究表明，尽管NbO具有高的NRR活性，但由于在NRR过程中容易形成低活性的氮氧化铌，因此它可能不是合适的NRR电催化剂。
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 μg h−1 mgcat.−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 N2 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 N2 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.