Synthesis and optical properties of turquoise-and green-colored brownmilleritetype Ba_2In_(2-x-y)Mn_xAl_yO_(5+x) codoped with manganese and aluminum

Brownmillerite-type oxides Ba_2In_（2-x-y）Mn_xAl_yO_（5＋x）（0 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.5） were prepared at 1300°C through solid-state reaction. X-ray diffraction（XRD） analysis showed that the structure symmetry evolved from orthorhombic to cubic with increasing Mn and Al contents. When y was greater than 0.3, peaks associated with small amounts of BaAl_2O_4 and Ba_2InAlO_5 impurities were observed in the XRD patterns. When substituted with a small amount of Mn（x ≤ 0.3）, the Ba_2In_（2-x-y）Mn_xAl_yO_（5＋x） samples exhibited an intense turquoise color. The color changed to green and dark-green with increasing Mn concentration. UV–vis absorbance spectra revealed that the color changed only slightly upon Al doping. The valence state of Mn ions in Ba_2In_（2-x-y）Mn_xAl_yO_（5＋x） was confirmed to be ＋5 on the basis of X-ray photoelectron spectroscopic analysis. According to this analysis, the intense turquoise color of the Ba_2In_（2-x-y）Mn_xAl_yO_（5＋x） samples is rooted in the existence of Mn^（5＋）; thus, the introduction of Al does not affect the optical properties of the compounds.

Three-dimensional nitrogen and phosphorous Co-doped graphene aerogel electrocatalysts for efficient oxygen reduction reaction

The development of efficient electrocatalysts for oxygen reduction reaction(ORR) is of importance for fuel cells and metal-air batteries. Herein, three-dimensional nitrogen and phosphorous co-doped graphene aerogel(NPGA) was prepared via the pyrolysis of polyaniline(PANi) coated graphene oxide aerogel synthesized by oxidative polymerization of aniline on graphene oxide(GO) sheets in the presence of phytic acid. The uniform coating of PANi thin layer on the surface of GO sheets enables the formation of highly porous composite aerogel of PANi and GO. The subsequent thermal treatment is able to prepare the porous NPGA due to the carbonization of PANi and phytic acid as nitrogen and phosphorous resources. When used as electrocatalysts,the as-prepared NPGA electrocatalysts exhibited good catalytic activity to ORR via an efficient four-electron pathway with good stability, benefiting from the highly porous structure and the heteroatom co-doping. More importantly, Zn-air batteries operated in ambient air have been fabricated by coupling a Zn plate with the NPGA electrocatalyst in an air electrode, demonstrating the maximal power density as high as ~260 W/g and a good long-term stability with slightly potential decay for over 450 h. The facile method for preparing efficient carbon based ORR electrocatalysts would generate other potential applications including fuel cells and others.