Facet effect of Co3O4 nanocrystals on visible-light driven water oxidation

The deep comprehension of water oxidation mechanisms and structure-activity relationships on heterogeneous catalysts remains challenging. Here, facet effect of model spinel Co3O4 on water oxidation driven by visible-light is investigated in a well-established [Ru(bpy)3]2+-S2O82− (bpy = 2,2-bipyridine) biomimetic system to unveil the internal water oxidation mechanism for the first time. Spinel Co3O4 catalysts in the morphologies of nanocube, nanorod and nanosheet are synthesized successfully by bottom-up nanotechnologies, and they predominantly expose the well-defined crystal planes of {100}, {110} and {112}, respectively. Using time-resolved laser flash photolysis approach, the dynamically electronic transfer in photocatalytic courses of three Co3O4 catalysts are distinguished in the nanosecond scale. The three model catalysts show a facet-dependent activity rule that the water oxidation performance of {112} is similar with that of {110} and much better than that of {100}. The Co2+-Co2+ active sites with an ionic distance of 3.495 Å for catalyzing water oxidation only appear in {112} and {110} planes except for {100}, which is possibly responsible for the unique activity order of three Co3O4 catalysts. Furthermore, the Co2+ ions in the tetrahedral sites of spinel Co3O4 are confirmed to be more active than the Co3+ ions in the octahedral sites under visible-light driven water oxidation. The new insights shed a light on developing advanced nanocatalysts for oxygen evolution reaction.