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

In Situ Synthesis of Manganese Oxide as an Oxygen Evolving Catalyst A New Strategy

All studies on oxygen-evolution reaction by Mn oxides in the presence of cerium(IV) ammonium nitrate (CAN) have been so far carried out by synthesizing Mn oxides in the first step. And then, followed by the investigation of the Mn oxides in the presence of oxidants for oxygen-evolution reaction (OER). This paper presents a case study of a new and promising strategy for in situ catalyst synthesis by the adding Mn-II to either CAN or KMnO4/CAN solution, resulting in the formation of Mn-based catalysts for OER. The catalysts were characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both compounds contained nano-sized particles that catalyzed OER in the presence of CAN. The turnover frequencies for both catalysts were 0.02 (mmolO2 /mol(Mn) center dot s)

Mechanistic Understanding of Water Oxidation in the Presence of a Copper Complex by In Situ Electrochemical Liquid Transmission Electron Microscopy

The design of molecular oxygen evolution reaction OER catalysts requires fundamental mechanistic studies on their widely unknown mechanisms of action. To this end, copper complexes keep attracting interest as good catalysts for the OER, and metal complexes with TMC TMC 1,4,8,11 tetramethyl 1,4,8,11 tetraazacyclotetradecane stand out as active OER catalysts. A mononuclear copper complex, [Cu TMC H2O ] NO3 2 TMC 1,4,8,11 tetramethyl 1,4,8,11 tetraazacyclotetradecane , combined both key features and was previously reported to be one of the most active copper complex based catalysts for electrocatalytic OER in neutral aqueous solutions. However, the functionalities and mechanisms of the catalyst are still not fully understood and need to be clarified with advanced analytical studies to enable further informed molecular catalyst design on a larger scale. Herein, the role of nanosized Cu oxide particles, ions, or clusters in the electrochemical OER with a mononuclear copper II complex with TMC was investigated by operando methods, including in situ vis spectroelectrochemistry, in situ electrochemical liquid transmission electron microscopy EC LTEM , and extended X ray absorption fine structure EXAFS analysis. These combined experiments showed that Cu oxide based nanoparticles, rather than a molecular structure, are formed at a significantly lower potential than required for OER and are candidates for being the true OER catalysts. Our results indicate that for the OER in the presence of a homogeneous metal complex based pre catalyst, careful analyses and new in situ protocols for ruling out the participation of metal oxides or clusters are critical for catalyst development. This approach could be a roadmap for progress in the field of sustainable catalysis via informed molecular catalyst design. Our combined approach of in situ TEM monitoring and a wide range of complementary spectroscopic techniques will open up new perspectives to track the transformation pathways and true active species for a wide range of molecular catalyst

Nickel Vanadium Layered Double Hydroxide under Water Oxidation Reaction New Findings and Challenges

Nickel-Vanadium Layered Double Hydroxide under Water-Oxidation Reaction: New Findings and Challenge