Oxygen electrochemistry is at the core of several emerging energy conversion technologies. The role of carbon nanostructures in the electrocatalysis of the oxygen reduction reaction is not well understood. Herein we report an investigation of the role of graphitic edges in oxygen electrochemistry. A new synthetic method was used to create all-carbon model electrode materials with controlled morphology. Electron microscopy results show that synthesized materials possess a high density of graphitic edges. Electrochemical intercalation experiments however indicate that the density of electroactive edges does not correlate positively with microscopy results. The materials were then characterized as electrodes for the oxygen reduction reaction in alkaline media. Results suggest that electrochemical determinations of edge and defect density more accurately predicts electrocatalytic activity thus suggesting that in situ characterization techniques are needed to understand the carbon/electrolyte interface.
Three-dimensional (3D) customized scaffolds capable to mimic a native extracellular matrix open new frontiers in cells manipulation and advanced therapy. The major challenge is in a proper substrate for in vitro models on engineered scaffolds, capable to modulate cells differentiation. Here for the first time we demonstrate novel design and functionality of the 3D porous scaffolds of aligned, self-assembled ceramic nanofibers of ultra-high anisotropy ratio (~107), augmented into graphene shells. This unique hybrid nano-network allows an exceptional combination of selective guidance stimuli of stem cells differentiation, immune reactions variations, and local immobilization of cancer cells, which was not available before. The scaffolds were shown to be able to direct human mesenchymal stem cells (important for stimulation of neuronal and muscle cells) preferential orientation, to suppress major inflammatory factors, and to localize cancer cells; all without additions of specific culture media. The selective downregulation of specific cytokines is anticipated as a new tool for understanding of human immune system and ways of treatment of associated diseases. The effects observed are self-regulated by cells only, without side effects, usually arising from use of external factors. New scaffolds may open new horizons for stem cells fate control such as towards axons and neurites regeneration (Alzheimer’s disease) as well as cancer therapy development.
In this work, a catalyst-free direct deposition of multi-layered graphene closed shells around highly aligned alumina nanofibers with aspect ratio of 107 is demonstrated for the first time. A single – step chemical vapor deposition process of specified parameters was used for development of hybrid structures of carbon shells around the core alumina nanofibers. Transmission electron microscopy and Raman spectroscopy were used to confirm formation of graphene layers and to understand the morphology of the various structures. The developed routine for growth of peculiar carbon nanostructures opens new opportunities for deposition of the tailored carbon structures on dielectric substrates.
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