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Water oxidation by copper (II) complex: New findings, questions, challenges and a new hypothesis

Abstract

Copper(II) complexes are very promising catalysts for water oxidation. Herein new findings for the water-oxidizing activity of a few copper(II) complexes under the water oxidation conditions are reported. Copper compounds in this study are copper(II) phthalocyanine-3,4′,4″,4″′-tetrasulfonic acid tetrasodium salt (1), the product from the hydrolysis of Cu(II)tptz(H2O)(CH3COO)2 (tptz: 2,4,6-tris(2-pyridyl)-s-triazine) (2), Cu(II)(phen)(CH3CN)2(ClO4)2 (3), Cu(II)(phen)2(CH3CN)(ClO4)2 (4), and copper(II) sulfate pentahydrate (Cu(II) salt), which were investigated in the context of the water-oxidation reaction by electrochemical and related methods. The experiments showed that among these compounds at pH = 11, only Cu(II) salt and 3 led to immediate water oxidation. On the other hand, for stable complexes: 1, 2 and 4 even after a few minutes low water oxidation rates were observed. The role of nanosized particles of Cu oxide or Cu ions for electrochemical water oxidation was investigated. Under the water-oxidation conditions, the electrode, Cu(II) complexes and Cu(II) salt were studied and a relationship between the stability of Cu(II) complex and water oxidation was suggested. It is proposed that Cu(II) ions or cluster than the starting copper(II) complex or copper(II) oxide are the true catalysts for the investigated water oxidation process for the short-term amperometry. For 3 and for long-term amperometry, CuOx was detected. The experiments showed that a molecular mechanism for the water-oxidation reaction in the presence of copper(II) complexes should be carefully analyzed to verify the role of copper ions or cluster formation for the water-oxidation reaction.

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Supplementary files

Publication details

The article was received on 09 May 2018, accepted on 07 Jun 2018 and first published on 07 Jun 2018


Article type: Paper
DOI: 10.1039/C8DT01876F
Citation: Dalton Trans., 2018, Accepted Manuscript
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    Water oxidation by copper (II) complex: New findings, questions, challenges and a new hypothesis

    M. M. Najafpour, S. Mehrabani, Y. Mousazade and M. Holynska, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT01876F

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