Yes, we CAN: Active mixed-valent MnOx water oxidation catalysts through partial oxidation of nanostructured MnO particles

Very Important Paper in Angewandte Chemie by Prof. Dau and Driess

Yes, we CAN: Partial oxidation of inactive MnO nanoparticles by Ce^IV as oxidant gives active MnO_x catalysts that are suitable for effective photochemical and electrochemical water oxidation. The active MnO_x catalyst contains mixed-valent Mn^II, Mn^III, and Mn^IV species (see picture; green and violet) interconnected through oxido bridges (red) with defects and disorders. MnO_x is analogous to calcium–manganese oxide systems where the calcium sites are replaced by Mn^II or Mn^III ions.

The unexpected facile conversion of catalytically inactive nanostructured MnO precursors  into active amorphous MnOx catalysts is report for the first time for effective water oxidation by using ceric ammonium nitrate (CAN) as an oxidant (“corrosion agent”). The effective photochemical water oxidation of the active catalysts has been carried out in the presence of [Ru(bpy)₃]²⁺ as a photosensitizer. 

Structural characterization of the active MnOx catalyst by XAS revealed the presence of Mn^II, Mn^III, and Mn^IV sites. A series of defects and structural disorder in the di-µ-oxido-bridged structure makes the catalyst analogous to calcium-manganese oxide systems, but the calcium sites are occupied by Mn^II, or Mn^III ions. 

In other words, the structural motif of the active MnOx catalyst is close to biomimetic water oxidation catalyst systems, which explains its efficient catalytic activity in water oxidation.

This paper of Holger Dau and Matthias Driess has been selected as a very important paper in Angewandte Chemie.

Angew. Chem. Int. Ed. 2013; DOI: anie.201307543
Published online 31 October 2013.

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