Highly active postspinel-structured catalysts for oxygen evolution reaction.

The rational design principle of highly active catalysts for the oxygen evolution reaction (OER) is desired because of its versatility for energy-conversion applications. Postspinel-structured oxides, Ca O ( = Cr, Mn, and Fe), have exhibited higher OER activities than nominally isoelectronic conventional counterparts of perovskite oxides LaO and spinel oxides Zn O. Electrochemical impedance spectroscopy reveals that the higher OER activities for Ca O series are attributed to the lower charge-transfer resistances.

Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO and SrFeO Perovskites.

The Ruddlesden-Popper (RP)-type layered perovskite is a candidate material for a new nitrogen oxide (NO) storage catalyst. Here, we investigate the adsorption and oxidation of NO on the (001) surfaces of RP-type oxide SrFeO for all of the terminations by comparing to those of simple perovskite SrFeO by the density functional theory (DFT) calculations. The possible (001) cleavages of SrFeO generate two FeO- and three SrO-terminated surfaces, and the calculated surface energies indicated that the SrO-terminated surface generated by the cleavage at the rock salt layer is the most stable one.

Complementary evaluation of structure stability of perovskite oxides using bond-valence and density-functional-theory calculations.

Estimation of structure stability is an essential issue in materials design and synthesis. Global instability index () based on bond-valence method is applied as a simple indication, while density functional theory calculation is adopted for accurate evaluation of formation energy. We compare the and total energy of typical O-type perovskite oxides and rationalize their relationship, proposing that the criteria for empirically unstable structures ( > 0.

Covalency Competition in the Quadruple Perovskite CdCuFeO.

Cadmium ions (Cd) are similar to calcium ions (Ca) in size, whereas the Cd ions tend to form covalent bonds with the neighboring anions because of the high electronegativity. The covalent Cd-O bonds affect other metal-oxygen bonds, inducing drastic changes in crystal structures and electronic states. Herein, we demonstrate high-pressure synthesis, crystal structure, and properties of a new quadruple perovskite CdCuFeO.

Bifunctional Oxygen Reaction Catalysis of Quadruple Manganese Perovskites.

Bifunctional electrocatalysts for oxygen evolution/reduction reaction (OER/ORR) are desirable for the development of energy conversion technologies. It is discovered that the manganese quadruple perovskites CaMn O and LaMn O show bifunctional catalysis in the OER/ORR. A possible origin of the high OER activity is the unique surface structure through corner-shared planar MnO and octahedral MnO units to promote direct OO bond formations.