Assembly of some composites of Keggin-type polyoxometalate bearing Zn/Cu-organic complexes as high capacity electrode materials

With the overuse of fossil energy and the destruction of ecological environment, it is urgent for the design and preparation of environmentally friendly and renewable energy storage supercapacitors (SCs) materials. Herein, four Keggin-based complexes [Zn4(Ccbypy)10(H2O)4(SiMo12O40)2]·8H2O (1), [Cu2(Ccbypy)4(H2O)2(SiMo12O40)]·3H2O (2), [Zn4(Ccbypy)10(H2O)4(SiW12O40)2]·6H2O (3) and [Cu2(Ccbypy)4(H2O)2(SiW12O40)]·4H2O (4), (Ccbupy = 4-Carboxy-1-(2′-cyano-biphenyl-4-ylmethyl)-pyridinium) are synthesized by hydrothermal method. Complexes 1 and 3 as well as 2 and 4 are isomorphous. Four complexes show unique two-dimensional supramolecular layers or three-dimensional supramolecular framework structures through hydrogen bonding interactions. Furthermore, 2–GCE demonstrates the largest cyclic voltammetry area and the best electrical conductivity in 2 M H3PO4 solution. Benefiting from the three-dimensional supramolecular framework formed by the intermolecular hydrogen bonding and the variable oxidation state of the Cu. 2–GCE exhibits an optimal capacitance of 1520.8 F g–1 at 1 A g–1 and excellent cycle stability with 96.61 % capacitance retention after 1000 cycles. Additionally, the SCs performance of 2–GCE is far better than that the many previous reported POMs-based materials. These POMs materials provide new idea and guidance for the synthesis of high-performance energy storage devices.