Treated Nanolayered Mn Oxide by Oxidizable Compounds: A Strategy To Improve the Catalytic Activity toward Water Oxidation.

Herein, we investigate the effect of post-treatment of nanolayered manganese oxide by different inorganic and organic compounds. We use the fact that nanolayered manganese oxides are among the strongest naturally occurring oxidants, capable of oxidizing a wide range of organic molecules. Post-treatment of the synthetic Mn oxides with oxidizable compounds increases the cerium(IV)-driven water oxidation catalyzed by treated layered manganese oxides more than 25 times. On the basis of X-ray absorption investigations, we attribute this effect to the increased amount of manganese(III) ions. This finding can explain some puzzles in water oxidation by manganese oxides and may help to advance toward an efficient design strategy of water-oxidizing catalyst in artificial photosynthetic systems.

The role of nano-sized manganese oxides in the oxygen-evolution reactions by manganese complexes: towards a complete picture.

Eighteen Mn complexes with N-donor and carboxylate ligands have been synthesized and characterized. Three Mn complexes among them are new and are reported for the first time. The reactions of oxygen evolution in the presence of oxone (2KHSO5·KHSO4·K2SO4) and cerium(iv) ammonium nitrate catalyzed by these complexes are studied and characterized by UV-visible spectroscopy, X-ray diffraction spectrometry, dynamic light scattering, Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, scanning electron microscopy, membrane-inlet mass spectrometry and electrochemistry. Some of these complexes evolve oxygen in the presence of oxone as a primary oxidant. CO2 and MnO4(-) are other products of these reactions. Based on spectroscopic studies, the true catalysts for oxygen evolution in these reactions are different. We proposed that for the oxygen evolution reactions in the presence of oxone, the true catalysts are both high valent Mn complexes and Mn oxides, but for the reactions in the presence of cerium(iv) ammonium nitrate, the active catalyst is most probably a Mn oxide.

Mechanism, decomposition pathway and new evidence for self-healing of manganese oxides as efficient water oxidizing catalysts: new insights.

The electrochemical water-oxidation reaction usually requires a catalyst to reduce the overpotential and Earth-abundant catalysts, like MnO2, are attracting much attention. Here we use chemometric analysis, EPR and UV-Vis spectroscopies to track Mn(II) and MnO4(-) byproducts to the reaction of a MnO2 film in the presence of cerium(IV) ammonium nitrate. Permanganate ion is involved in at least two key reactions: it may oxidize water to O2 or can combine with Mn(II) to remake MnO2 solid. We propose mechanisms for water oxidation and present a self-healing process for this reaction.