Electrocatalytic reduction of O₂ by a Cu(II)-substituted electron-rich wheel-type oxomolybdate nanocluster

Catalysis of electron transfer by a Cu-substituted wheel-type oxomolybdate cluster-anion, [(H₄Cu₅^II)Mo₂₈ ^VMo₁₁₄^VIO₄₃₂(H₂O) ₅₈]^26-, {Mo₁₄₂Cu₅}, (1), is demonstrated. Data provided include aqueous-solution chemistry (stability) studies of 1 and [Mo₂₈^VMo₁₁₄^VIO ₄₃₂(H₂O)₅₈H₁₄]^26-, {Mo₁₄₂}, (2), derivatives of the "plenary" {Mo ₁₅₄} anion, [Mo₂₈^VMo₁₂₆ ^VIO₄₆₂(H₂O)₇₀H₁₄] ^14-, (3). Combined use of cyclic voltammetry and UV-vis spectroscopy shows that, while both 1 and 2 appear to be stable in solution at pH 0.33 (0.5 M H₂SO₄), 1 is more stable than 2 at pH 3 (in 0.2 M Na ₂SO₄). Cyclic voltammetric analysis in the presence of O₂ shows that 1 is an electrocatalyst for electron transfer to O ₂. Bulk electrolysis of 1 in the presence of O₂ (ca. 1 mM) is used to assess catalyst stability under turnover conditions, and to demonstrate that the final product of electrocatalytic reduction is water, rather than H₂O₂. Finally, control experiments using 1, 2, and CuSO₄ (no oxomolybdate-cluster present), show that catalytic activity is due to specific interaction(s) between Cu ions and the Mo ₁₄₂ type oxomolybdate structure of 1.