Amorphous Cobalt Oxide Nanoparticles as Active Water‐Oxidation Catalysts

Abstract Artificial photosynthesis requires the practical use of efficient, robust, and economical water‐oxidation catalysts (WOCs) for chemical‐fuel production. The synthesis of amorphous cobalt oxide nanoparticles (ca. 2 nm) is reported as a WOC with a turnover frequency up to 8.6 s −1 in the photocatalytic Ru(bpy) 3 2+ –Na 2 S 2 O 8 system (bpy=2,2′‐bipyridyl). This activity is unprecedented in heterogeneous cobalt‐based WOCs and is even comparable to that of a state‐of‐the‐art homogeneous cobalt‐based polyoxometalate catalyst. With the help of experimental and computational X‐ray absorption spectroscopy, the atomic structure of the synthesized amorphous cobalt oxide nanoparticles was characterized, and it consists of a one‐dimensional chain of dimeric edge‐sharing CoO 6 octahedra. Theoretical calculations suggest that this structure was able to promote O−O bond coupling, unlike crystalline cobalt oxide WOCs, which led to the enhanced water‐oxidation activity.