Redesign of Carbon Materials for Novel Storage, Mechanical and Optical Properties
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Redesign of Carbon Materials for Novel Storage, Mechanical and Optical Properties Stefano Leoni1, Igor A. Baburin1, S. E. Boulfelfel2, D. Selli1 1 2
Technische Universität Dresden, Institut für Physikalische Chemie, 01062 Dresden, Germany Stony Brook University, Department of Geosciences, New York 11794-2100, USA
ABSTRACT We revisit the polymorphism of carbon along two directions. First, we discover novel polymorphs in the vicinity of graphite, with outstanding optical and mechanical properties. Using numerical methods and graph-theoretical tools, we find as many as 4 novel superhard and transparent polymorphs, with great technological potential. Second, scaling up a model of rod packing to carbon nanotube (CNT) scaffoldings, we discover that such complex assemblies of CNTs are outstanding adsorbers of hydrogen, capable of reaching the DOE target (~6.0 wt% at ambient conditions). Along this line, we highlight novel paradigms for revisiting carbon, in view of remarkable qualities and superior properties. INTRODUCTION Carbon remains the most versatile material. In the era of energy efficiency and reversible storage, carbon has the potential of providing clean and very effective solutions within an upcoming hydrogen economy. The polymorphism of carbon has been the object of repeated surprise over the years. Novel forms, ranging from extended (graphene) to finite (nanotubes and fullerenes) have appeared, with outstanding properties [1]. In this work we review recent results on the polymorphism of carbon along two lines: a) novel superhard and transparent sp3 carbon materials [2, 3], b) carbon nanotubes assemblies with superior hydrogen storage properties [4]. The quest for carbon materials with enhanced mechanical properties and a modified optical gap is a topic of high priority. Property engineering is tightly connected with the ability to predict crystal structures, which remains a central issue in both basic solid-state research and modern materials science. In the effort of achieving superior materials for hydrogen storage and gas segregation, structure prediction stands out for its capacity to efficiently indicate viable target compounds. The identification of metastable modifications that can exhibit interesting physical and chemical properties is the central challenge of numerical approaches to predicting materials. A recent scientific challenge consists in identifying the crystalline product of cold graphite compression. At high pressures and high temperatures graphite is transformed into diamond. Cold compression on the contrary produces a hard and transparent product, which is nonetheless different either from cubic or hexagonal diamond [5]. Recent works deal with the nature of this product of cold graphite compression [6]. The two energetically most preferable candidates so far, M- and W-carbon, can be considered as parallel sets of corrugated graphene sheets interconnected by odd rings fused into characteristic ‘5+7’ patterns. Following this structural principle, other possibilities may arise.
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