Homogeneous Cobalt/Vanadium Complexes as Precursors for Functionalized Mixed Oxides in Visible‐Light‐Driven Water Oxidation

Abstract

The heterometallic complexes (NH₄ )₂ [Co(H₂ O)₆ ]₂ [V₁₀ O₂₈ ]⋅4 H₂ O (1) and (NH₄ )₂ [Co(H₂ O)₅ (β-HAla)]₂ [V₁₀ O₂₈ ]⋅4 H₂ O (2) have been synthesized and used for the preparation of mixed oxides as catalysts for water oxidation. Thermal decomposition of 1 and 2 at relatively low temperatures (<500 °C) leads to the formation of the solid mixed oxides CoV₂ O₆ /V₂ O₅ (3) and Co₂ V₂ O₇ /V₂ O₅ (4). The complexes (1, 2) and heterogeneous materials (3, 4) act as catalysts for photoinduced water oxidation. A modification of the thermal decomposition procedure allowed the deposition of mixed metal oxides (MMO) on a mesoporous TiO₂ film. The electrodes containing Co/V MMOs in TiO₂ films were used for electrocatalytic water oxidation and showed good stability and sustained anodic currents of about 5 mA cm^-2 at 1.72 V versus relative hydrogen electrode (RHE). This method of functionalizing TiO₂ films with MMOs at relatively low temperatures (<500 °C) can be used to produce other oxides with different functionality for applications in, for example, artificial photosynthesis.