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Cluster size and composition dependent water deprotonation by free manganese oxide clusters.
Phys Chem Chem Phys ; 18(23): 15727-37, 2016 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-27226138
ABSTRACT
In the quest for cheap and earth abundant but highly effective and energy efficient water splitting catalysts, manganese oxide represents one of the materials of choice. In the framework of a new hierarchical modeling strategy we employ free non-ligated manganese oxide clusters MnxOx+y(+) (x = 2-5, y = -1, 0, 1, 2) as simplified molecular models to probe the interaction of water with nano-scale manganese oxide materials. Infrared multiple-photon dissociation (IR-MPD) spectroscopy in conjunction with first-principles spin density functional theory calculations is applied to study several series of MnxOx+y(H2O)n(+) complexes and reveal that the reaction of water with MnxOx+y(+) leads to the deprotonation of the water molecules via hydroxylation of the cluster oxo-bridges. This process is independent of the formal Mn oxidation state and occurs already for the first adsorbed water molecule and it proceeds until all oxo-bridges are hydroxylated. Additional water molecules are bound intact and favorably form H3O2 units with the hydroxylated oxo-bridges. Water adsorption and deprotonation is also found to induce structural transformations of the cluster core, including dimensionality crossover. Furthermore, the IR-MPD measurements reveal that clusters with one oxygen atom in excess MnxOx+1(+) contain a terminal O atom while clusters with two oxygen atoms in excess MnxOx+2(+) contain an intact O2 molecule which, however, dissociates upon adsorption of a minimum number of water molecules. These basic concepts could aid the future design of artificial water-splitting molecular catalysts.

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Texto completo: Disponível Coleções: Bases de dados internacionais Base de dados: MEDLINE Idioma: Inglês Revista: Phys Chem Chem Phys Assunto da revista: Biofísica / Química Ano de publicação: 2016 Tipo de documento: Artigo País de afiliação: Alemanha