Cobalt and cobalt oxides N-codoped porous carbon derived from metal-organic framework as bifunctional catalyst for oxygen reduction and oxygen evolution reactions.

Metal-organic framework (MOF)-derived transition metal/metal oxide-carbon hybrids are promising cost-effective electrocatalysts to replace noble metal catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Co@CoO@Co3O4-N/C was prepared by two-step thermal treatment of Co-MOF ([Co(INA)2]·0.5EtOH) (INA: isonicotinic acid). Firstly, Co-MOF, as precursor, was pyrolyzed at different temperatures in N2 atmosphere to obtain Co-N/C-T (T = 700, 800, 900 °C) materials among which Co-N/C-800 shows remarkably high ORR activity. After oxidation treatment, Co-N/C-800 is transformed into Co@CoO@Co3O4-N/C which exhibits enhanced electrocatalytic activities for both ORR and OER. The as-obtained Co@CoO@Co3O4-N/C has more positive onset potential (-0.136 V vs. Ag/AgCl) and higher limit current density (4.9 mA cm-2) than Co-N/C-800 (-0.143 V vs. Ag/AgCl and 3.9 mA cm-2), as well as better tolerance to methanol and stability (80.0%) than those of Pt/C (63.2%) for ORR. Co@CoO@Co3O4-N/C also displays outstanding OER performances, with lower overpotential (450 mV) than that of Co-N/C-800 (492 mV) at a current density of 10 mA cm-2. The excellent electrochemical performance of Co@CoO@Co3O4-N/C can be ascribed to uniformly dispersed Co-Nx active sites, strong synergistic effects between N-doped carbon support and Co@CoO@Co3O4 as well as ordered mesoporous structure, boosting mass transfer and accelerating electrocatalytic reaction.

[Diversity of soil bacterial community in banana orchards infected with wilt disease].

Six soil samples including 3 wilt disease-infected samples and 3 disease-free samples were collected from the banana orchards in 3 areas in Lingao County, Hainan Province of South China. The soil physical and chemical properties were determined by conventional methods, and the diversity of soil bacterial community was analyzed by terminal restriction fragment length polymorphism (T-RFLP). Then, the relationships between the soil bacterial community composition and the soil physical and chemical properties were investigated. In the same areas, most of the soil physical and chemical properties were poorer in disease-infected than in disease-free banana orchards, with the most obvious difference in soil available P content and pH. The T-RFLP analysis showed the diversity of soil bacterial community was richer in disease-infected than in disease-free banana orchards. The lengths of the dominant T-RFs in the 3 areas were 144, 147 and 233 bp, respectively. Through the comparison with phylogenetic assignment tool, it was deduced that the dominant species in the 3 areas were Bacillus subtilis, Staphylococcus and Eubacterium ruminantium. The distribution of most T-RFs was related to the soil alkaline hydrolyzable N, available K, available P and water content, and the relative abundance of most T-RFs was richer in disease-infected than in disease-free banana orchards.