The Catalytic Properties Of Dinuclear Copper And Iron Complexes For Water Oxidation

Hydrogen is a pollution-free and renewable energy, and the development of hydrogen energy is considered to be a great way to solve the problem of energy sustainably. There is abundant water on the earth, and using water as the material to prepare hydrogen is regarded as one of the most economic method. Water oxidation, a complicated reaction involving the transfer of four electrons with a high energy barrier, is a bottleneck in the process of splitting water into hydrogen and oxygen. Therefore, how to synthesize highly efficient and stable water oxidation catalysts is an important research topic. Transition metal complexes with a wealth of optics, redox properties and catalytic performance have attracted much attention. So far, most reported water oxidation catalysts contain precious metals such as ruthenium and iridium. Recently, researchers have focused on the complexes of non-precious metals, especially those of manganese, copper, iron and cobalt. Compared with the precious metal catalysts, those based on the first transition metal complexes will have a low cost and a broad prospect of application. In this work, some dinuclear copper and iron complexes have been synthesized and their catalytic activities for water oxidation studied. The research work is as follows:1. Two dinuclear copper complexes [Cu2(tpbn)(CH3OH)4(ClO4)2](ClO4)2 (1),[Cu2(tpbn)(2,2’-bpy)2](C104)4(CH3COCH3)2(2)(tpbn=N,N,N’,N’-tetrakis(2-pyridinemethy-1)-1,4-butyldiamine; 2,2’-bpy=2,2’-bipyridine) have been synthesized and their structures determined by X-ray single crystallographic diffraction. The Cu(II) center of (1) is six-coordinated with a distorted octahedron geometry, while that Cu(II) center of (2) is five-coordinated with a square pyramidal geometry. Each tpbn chelates and bridges two Cu(II) ions.2. In the buffer solution of CH3COONa-NaOH, the catalytic activities of complexes (1) and (2) for water oxidation under different pH and concentrations have been investigated. When potassium hydrogen sulfate was used as the oxidant, (1) showed the best catalytic activity at pH 12.50 with a turnover number (TON) of 2.4. Under the same conditions, the TON value of (2) is 3.8. The electrocatalytic activities of both (1) and (2) have also been investigated. The onset potentials for water oxidation are at around 0.8 V.3. Three dinuclear iron complexes [Fe2O(C12H8N2)4](H2O)2(ClO4)4 (3) (Ci2H8N2= 1,10-phenanthroline), [Fe20(C10H8N2)4](H20)2(ClO4)4 (4) (C10H8N2 = 2,2’-pyridine), [Fe2O(C12H12N2)4](H2O)2(ClO4)4 (5) (C12H,2N2= 4,4’-dimethyl-2,2’-bipyridine) have been synthesized and their catalytic activities for water oxidation investigated. In the buffer solution of CH3COOH-CH3COONa, the catalytic activities of (3)-(5) for water oxidation under different pH and concentrations have been studied. When potassium hydrogen sulfate was used as the oxidant, (3) showed the best catalytic activity at pH= 4.50, and the TON value is 3.8. Complex (4) exhibited the best catalytic activity at pH= 3.45 with a TON value of 7.7. Complex (5) showed the best catalytic activity at pH= 7.00 with a TON value of 12.3. The electrocatalytic activities of (3)-(5) in CH3COOH-CH3COONa solutions at pH= 7.50 have been investigated. The onset potentials for water oxidation of three complexes are at around 1.20 V.