Cation Substitution Strategy for Developing Perovskite Oxide with Rich Oxygen Vacancy-Mediated Charge Redistribution Enables Highly Efficient Nitrate Electroreduction to Ammonia

• Published in: Journal of the American Chemical Society 2023-10, Vol.145 (39), p.21387-21396
• Main Authors: Chu, Kaibin, Zong, Wei, Xue, Guohao, Guo, Hele, Qin, Jingjing, Zhu, Haiyan, Zhang, Nan, Tian, Zhihong, Dong, Hongliang, Miao, Yue-E., Roeffaers, Maarten B. J., Hofkens, Johan, Lai, Feili, Liu, Tianxi
• Format: Article
• Language: English
• Subjects: ammonia; cations; density functional theory; energy; hybridization; hydrogen production; nitrates; oxygen
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.3c06402

The electrocatalytic nitrate (NO3 –) reduction reaction (eNITRR) is a promising method for ammonia synthesis. However, its efficacy is currently limited due to poor selectivity, largely caused by the inherent complexity of the multiple-electron processes involved. To address these issues, oxygen-vacancy-rich LaFe0.9M0.1O3−δ (M = Co, Ni, and Cu) perovskite submicrofibers have been designed from the starting material LaFeO3−δ (LF) by a B-site substitution strategy and used as the eNITRR electrocatalyst. Consequently, the LaFe0.9Cu0.1O3−δ (LF0.9Cu0.1) submicrofibers with a stronger Fe–O hybridization, more oxygen vacancies, and more positive surface potential exhibit a higher ammonia yield rate of 349 ± 15 μg h–1 mg–1 cat. and a Faradaic efficiency of 48 ± 2% than LF submicrofibers. The COMSOL Multiphysics simulations demonstrate that the more positive surface of LF0.9Cu0.1 submicrofibers can induce NO3 – enrichment and suppress the competing hydrogen evolution reaction. By combining a variety of in situ characterizations and density functional theory calculations, the eNITRR mechanism is revealed, where the first proton–electron coupling step (*NO3 + H+ + e– → *HNO3) is the rate-determining step with a reduced energy barrier of 1.83 eV. This work highlights the positive effect of cation substitution in promoting eNITRR properties of perovskites and provides new insights into the studies of perovskite-type electrocatalytic ammonia synthesis catalysts.