(765d) Mesoporous Spinels As Efficient Oxygen Evolution Catalysts

Solar energy harvesting in a sustainable and efficient way is more important today than ever before. One promising approach is to produce energy-rich solar fuels, e.g. hydrogen and methanol, from abundant resources, e.g. CO₂ and H₂O through an artificial photosynthetic approach. Regardless of the details in various methodologies, oxygen evolution from water holds the key to an efficient artificial photosynthetic system, because water is the only potential electron and proton source on earth that is capable to support terawatt scale energy products. Also, in order to achieve efficient solar fuel production, a higher TOF (100 s^-1nm^-2) is required for keeping up with the photon flux at high solar intensity. It is known that Pt is capable to reduce proton to hydrogen at a rate of 290 s^-1 per surface atom. Therefore, oxygen-evolving from water is the rate-limiting step and searching for efficient water oxidation catalysts is vital for building up an efficient solar fuel system.

Recent progress indicates that cobalt and manganese spinels could be highly efficient water oxidation catalysts. Although the origin of high activity is still unclear, it has been hypothesized that the metal sitting in the octahedral sites dominates the overall performance of spinel catalyst because of its cubane structure. Here, we will show our recent studies in mesoporous binary spinel systems, which suggest the metal sitting at the tetragonal site has huge impact on the water oxidation activity of spinel catalysts. A wide range of AB₂O₄ mixed oxide spinels with highly ordered mesoporous structures have been synthesized for the first time and their structures have been carefully characterized. The photocatalytic oxygen evolution activities of as-prepared samples were investigated using Ru(bpy)₃²⁺/Na₂S₂O₈ method. The preliminary results indicate the element at tetragonal sites has significant impact on the overall photocatalytic activities.

References:

1.   Rosen, J., Hutchings, G. S., & Jiao, F. Ordered Mesoporous Cobalt Oxide as Highly Efficient Oxygen Evolution Catalyst. Journal of the American Chemical Society 135, 4516-4521 (2013).

2.   Rosen, J., Hutchings, G. S., & Jiao, F. Synthesis, Structure, and Photocatalytic Properties of Ordered Mesoporous Metal-doped Co₃O₄. Journal of Catalysis (in press).