Bifunctional Electro-Catalysts Stemmed from Ln-Substituted Monovacant/Saturated Keggin Polyoxotungstates and Cu-Terpyridine Chlorides

Abstract

Three inorganic–organic hybrids based on monovacant/saturated polyoxotungstates and 3d-4f metal chlorides: [Cu2(tpy)2][Sm(H2O)3K(α-HSiW11O39)]Cl·2H2O (1), [Cu2(tpy)2][Eu(H2O)3K(α-HSiW11O39)]Cl·2H2O (2), Cu4Cl4(tpy)4(α-SiW12O40)]·2H2O (3), (tpy = 2,2′:6′,2″-terpyridine), were fabricated in the same POW/Ln/Cu-tpy reaction systems by adjusting pH. Compounds 1 and 2 display 1D circle-connecting-circle chain structure featured by {Ln–α–SiW11} polyoxoanion clusters and {Cu/tpy} units. Compound 3 with 3D supramolecular structure consists of saturated α-SiW12 clusters and [Cu2Cl2(tpy)2]2+ motifs. Compounds 1–3 exhibit bifunctional electro-catalytic behaviors for not merely reduction of nitrite but also oxidation of ascorbic acid. Electrocatalytic tests make clear that Sm-substituted hybrid based on POWs exhibits better activity than that for Eu-substitued/statured Keggin hybrids for electrocatalytic reduction of nitrite, statured Keggin hybrid shows better electro-catalytic performance for oxidations of ascorbic acid than those for Ln-substituted hybrids. The differences of electro-catalytic performances among three hybrids should be attributing to the distinctions of structures and electrochemical properties. Three inorganic-organic hybrids based on monovacant/saturated polyoxotungstates and 3d–4f metal chlorides were fabricated in the same POM/Ln/Cu-tpy reaction systems by adjusting pH. Compounds 1 and 2 display 1D circle-connecting-circle chain structure featured by {Ln–α–SiW11} polyxoanion clusters and {Cu/tpy} units, Compound 3 with 3D supramolecular structure consists of saturated α-SiW12 clusters and [Cu2Cl2(tpy)2]2+ motifs. Cyclic voltammetries of n-CPEs (n = 1–3) displayed bifunctional electrocatalytic activities toward reduction of nitrite and oxidation of ascorbic acid.