Iron Modified Graphitized Carbon Aerogels for Sustainable Energy Applications
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Iron Modified Graphitized Carbon Aerogels for Sustainable Energy Applications Praveen Kolla1, Kimberly Kerce2, Yong Zhao2, Joseph Houk3, Yahaya Normah3, Wendell Rhine4 and Alevtina Smirnova2 1 Material Engineering Science, 2Chemistry and Applied Biological Sciences, and 3Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701 4 Aspen Aerogel Inc., Northborough, MA 01532, USA ABSTRACT Mesoporous carbon aerogel has been impregnated with iron (10 and 15 wt. %) as a catalyst for graphitization by wet incipient method. The iron modified and non-modified carbon aerogels were heat treated at 900oC, 1200oC, and 1400oC in argon. The crystal structure, morphology, and electro catalytic activity of the resulting nano-composites have been studied. It was found that, the degree of graphitization was proportional to the concentration of Iron phase and the ratio of iron to iron nitride phase in the heat-treated samples. In carbon aerogel sample sintered at 1200oC with 15 wt. % of iron phase, mesoporosity in the range of 3-4 nm and microporosity (< 2nm) was significantly improved by graphitization without affecting the Carbon Aerogels mesoporosity in 10-30 nm range. In this case of 15 wt. % iron doped samples, HRTEM analysis confirms the presence of uniformly distributed ~43.5nm iron nanoparticles surrounded by graphene layers. Correspondingly, improved graphitization and presence of iron nitride resulted in 3.65 electron assisted oxygen reduction reaction. INTRODUCTION The materials for sustainable energy applications (e.g. protons exchange membrane fuel cells, super capacitors, and batteries) require high surface area, chemical stability and high electric conductivity. Sol-gel derived carbon aerogels (CA) with controlled surface area, porosity, and bulk chemistry have been successfully used for sustainable energy applications [1]. However, sp2-hybradized graphene and carbon nanotubes (CNT) show better electrical conductivity and chemical stability compared to amorphous carbon aerogels [2]. To increase the level of graphitization and electrochemical stability while retaining porosity, transition metal impregnated carbon aerogels have been studied. In presence of transition metals, high level of graphitization was obtained at significantly lower temperatures, than that in absence of the catalyst [3]. Graphitized carbon aerogels in the form of nanostructured rings, onions, and ribbons have been reported earlier when different transition metal doped carbon materials were treated under various conditions [4-7]. Nitrogen doping during graphitization in presence of transition metals improved four electron transfer supported oxygen reduction along with better chemical stability in acidic media [8, 9]. On other hand, transition metal doped carbon monoliths were successfully used for the direct single and MWCNT growth in the presence of carbon gaseous source in reduced environments [10-12]. The graphitization of transition metal doped carbon aerogels followed by CNT growth can improve mesoporo
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