Observation of active sites for oxygen reduction reaction on nitrogen-doped multilayer graphene

Active sites and the catalytic mechanism of nitrogen-doped graphene in an oxygen reduction reaction (ORR) have been extensively studied but are still inconclusive, partly due to the lack of an experimental method that can detect the active sites. It is proposed in this report that the active sites on nitrogen-doped graphene can be determined via the examination of its chemical composition change before and after ORR. Synchrotron-based X-ray photoelectron spectroscopy analyses of three nitrogen-doped multilayer graphene samples reveal that oxygen reduction intermediate OH(ads), which should chemically attach to the active sites, remains on the carbon atoms neighboring pyridinic nitrogen after ORR. In addition, a high amount of the OH(ads) attachment after ORR corresponds to a high catalytic efficiency and vice versa. These pinpoint that the carbon atoms close to pyridinic nitrogen are the main active sites among the different nitrogen doping configurations.

Enhancing the carbon yield of cellulose based carbon fibres with ionic liquid impregnates

Here we show that ionic liquids (ILs), protic or aprotic in nature containing a phosphate anion, can be used as effective impregnating compounds resulting in a 50% improvement of the carbon yield of cellulose based carbon fibres and a 70 °C reduction in the onset of the depolymerization temperature. Using 13C NMR and FTIR spectra, we characterize the carbonized fibres with and without IL impregnates. The oxidative step in the formation of carbon fibres from cellulose precursors is very important in determining the final material properties, as such we examine this stage and show that the IL reduces the onset of the cellulose depolymerization temperature while improving the oxidative stability. This study highlights the ability of ILs to act as novel impregnates which can successfully reduce the formation of tar and volatile substances during carbonization of cellulose based carbon fibres resulting in an improved carbon yield and significant cost savings due to reduced maintenance and wear of equipment. This journal is

Thermal and rheological characteristics of biobased carbon fiber precursor derived from low molecular weight organosolv lignin

In the present work, electrospinnability as well as thermal, rheological, and morphological characteristics of low molecular weight hardwood organosolv lignin, as a potential precursor for carbon fiber, was investigated. Submicromter biobased fibers were electrospun from a wide range of polymer solutions with different ratios of organosolv lignin to polyacrylonitrile (PAN). Rheological studies were conducted by measuring viscosity, surface tension, and electrical conductivity of hybrid polymer solutions, and used to correlate electrospinning behavior of solutions with the morphology of the resultant electrospun composite fibers. Using scanning electron microscopy (SEM) images, the solutions that led to the formation of bead-free uniform fibers were found. Differential scanning calorimetry (DSC) analysis revealed that lignin-based fibers enjoy higher decomposition temperatures than that of pure PAN. Thermal stability of the lignin-based fibers was investigated by thermogravimetric analysis (TGA) indicating a high carbon yield of above 50% at 600 °C, which is highly crucial in the production of low-cost carbon fiber. It was also observed that organosolv lignin synergistically affects thermal decomposition of composite fibers. A significant lower activation energy was found for the pyrolysis of lignin-derived electrospun fibers compared to that of pure PAN.

Comparison of marine macrophytes for their contributions to blue carbon sequestration

Many marine ecosystems have the capacity for long-term storage of organic carbon (C) in what are termed "blue carbon" systems. While blue carbon systems (saltmarsh, mangrove, and seagrass) are efficient at long-term sequestration of organic carbon (C), much of their sequestered C may originate from other (allochthonous) habitats. Macroalgae, due to their high rates of production, fragmentation, and ability to be transported, would also appear to be able to make a significant contribution as C donors to blue C habitats. In order to assess the stability of macroalgal tissues and their likely contribution to long-term pools of C, we applied thermogravimetric analysis (TGA) to 14 taxa of marine macroalgae and coastal vascular plants. We assessed the structural complexity of multiple lineages of plant and tissue types with differing cell wall structures and found that decomposition dynamics varied significantly according to differences in cell wall structure and composition among taxonomic groups and tissue function (photosynthetic vs. attachment). Vascular plant tissues generally exhibited greater stability with a greater proportion of mass loss at temperatures > 300 degrees C (peak mass loss -320 degrees C) than macroalgae (peak mass loss between 175-300 degrees C), consistent with the lignocellulose matrix of vascular plants. Greater variation in thermogravimetric signatures within and among macroalgal taxa, relative to vascular plants, was also consistent with the diversity of cell wall structure and composition among groups. Significant degradation above 600 degrees C for some macroalgae, as well as some belowground seagrass tissues, is likely due to the presence of taxon-specific compounds. The results of this study highlight the importance of the lignocellulose matrix to the stability of vascular plant sources and the potentially significant role of refractory, taxon-specific compounds (carbonates, long-chain lipids, alginates, xylans, and sulfated polysaccharides) from macroalgae and seagrasses for their long-term sedimentary C storage. This study shows that marine macroalgae do contain refractory compounds and thus may be more valuable to long-term carbon sequestration than we previously have considered.