title: Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation.
abstract: Previous measurements show that calcium manganese oxide nanoparticles are better water oxidation catalysts than binary manganese oxides (Mn3O4, Mn2O3, and MnO2). The probable reasons for such enhancement involve a combination of factors: The calcium manganese oxide materials have a layered structure with considerable thermodynamic stability and a high surface area, their low surface energy suggests relatively loose binding of H2O on the internal and external surfaces, and they possess mixed-valent manganese with internal oxidation enthalpy independent of the Mn(3+)/Mn(4+) ratio and much smaller in magnitude than the Mn2O3-MnO2 couple. These factors enhance catalytic ability by providing easy access for solutes and water to active sites and facile electron transfer between manganese in different oxidation states.
authors.affiliation: Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit, University of California, Davis, CA 95616, USA.
authors.forename: Nancy
authors.initials: N
authors.lastname: Birkner
authors.forename: Sara
authors.initials: S
authors.lastname: Nayeri
authors.forename: Babak
authors.initials: B
authors.lastname: Pashaei
authors.forename: Mohammad Mahdi
authors.initials: MM
authors.lastname: Najafpour
authors.forename: William H
authors.initials: WH
authors.lastname: Casey
authors.forename: Alexandra
authors.initials: A
authors.lastname: Navrotsky
mesh_terms: D017610:Calcium Compounds / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002384:Catalysis; D017895:Manganese Compounds / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D013816:Thermodynamics; D013818:Thermogravimetry; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D017610:Calcium Compounds; D017895:Manganese Compounds; D010087:Oxides; D014867:Water; C027424:manganese oxide
keywords: nanomaterials; thermochemistry