Sub-2 nm cobalt oxide cluster catalyst supported on alumina for efficient water oxidation

• Sub-2 nm cobalt oxide clusters supported on alumina were synthesized through mild oxidation of molecularly dispersed Co4(CO)12 precursor.
• The turnover frequency (TOF) of water oxidation on sub-2 nm CoOx clusters can reach as high as 0.067 s−1.
• The remarkably enhanced activity of cobalt oxide cluster is attributed to its more surface-exposed cobalt atoms and higher intrinsic activity.

Earth-abundant cobalt oxides as active water oxidation catalysts have attracted extensive attention, but the controlled synthesis of small cobalt oxide clusters still remains challenging. Herein we introduce a novel approach to deposit small cobalt oxide clusters on alumina which involves mild oxidation of molecularly dispersed Co4(CO)12 precursor. Scanning transmission electron microscope (STEM) shows that the size of prepared CoOx clusters is smaller than 2 nm. Turnover frequency (TOF) value of water oxidation on the synthesized cobalt oxide clusters can reach as high as 0.067 s−1 in photochemical Ru(bpy)32+-Na2S2O8 system, which is at least an order of magnitude higher than bulk cobalt oxide nanoparticles. The remarkably enhanced activity of cobalt oxide cluster is attributed to its more surface-exposed cobalt atoms and higher intrinsic activity.

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