Electrocatalytic Nitrate Reduction by a Cobalt Protoporphyrin Immobilized on a Pyrolytic Graphite Electrode

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• 作者：Jing Shen ; Yuvraj Y. Birdja ; Marc T. M. Koper
• 刊名：Langmuir
• 出版年：2015
• 出版时间：August 4, 2015
• 年：2015
• 卷：31
• 期：30
• 页码：8495-8501
• 全文大小：391K
• ISSN：1520-5827

文摘

A series of simple molecular catalysts, i.e., Co(III), Fe(II), Ni(II), Cu(II), and Rh(II) protoporphyrins (metal-PP), directly adsorbed on pyrolytic graphite have been utilized for catalyzing the electrochemical reduction of nitrate. These catalysts are studied by combining cyclic voltammetry with online electrochemical mass spectrometry (OLEMS) to monitor volatile products and online ion chromatography (IC) to detect ionic products in the aqueous electrolyte solution. Among all investigated porphyrins, the Co-based protoporphyrin shows the highest selectivity toward hydroxylamine (NH₂OH), which made it the catalyst of primary interest in the article. The reactivity and selectivity of the immobilized Co-protoporphyrin depend significantly on pH, with more acidic conditions leading to higher reactivity and higher selectivity toward hydroxylamine over ammonia. Potential controlled electrolysis results show that the potential also greatly influences the selectivity: at pH 1, hydroxylamine is the main product around 鈭?.5 V with approximately 100% selectivity, while hydroxylamine and ammonia are both formed at a more negative potential, 鈭?.75 V. The mechanism of the reaction is discussed, invoking of the possibility of two pathways for hydroxylamine/ammonia formation: a sequential pathway in which hydroxylamine is produced as an intermediate, with ammonia subsequently formed through the reduction of NH₂OH/NH₃OH⁺, and a parallel pathway in which the formation of hydroxylamine and ammonia is derived from a common intermediate.