Over 90% of world energy generation and consumption rely on thermal transport, conversion, or storage processes, the performance of which is often limited by materials thermal properties. These materials limitations have motivated us to investigate how thermal conductivity, thermoelectric power factor, and heat of fusion may be modified at the nanoscale to exceed the current limits. One recent focus of our work is on graphene, bismuth telluride atomic layers, and other two-dimensional (2D) atomic layer materials because some of the highest thermal conductivity or thermoelectric figure of merit values have been found in their bulk counter parts. In one work, we found that reducing the thickness of graphite toward single- or few- atomic layer graphene can increase or decrease its record-high basal-plane thermal conductivity, depending on whether the obtained 2D materials are suspended or supported. Similar size effects are observed in 2D hexagonal boron nitride and bismuth telluride, the latter of which also exhibits intriguing thickness dependence of the thermoelectric power. We further demonstrated continuous foams of 2D building blocks as an effective architecture to overcome the interface thermal resistance bottleneck, which has limited the conductivity of percolated nanostructure networks. These three-dimensional covalent networks of 2D graphene and h-BN are loaded into phase change materials to increase the power capacity of thermophysical storage systems.

Engineering thermal energy transport, conversion, and storage with 2D materials

247th National Meeting (2014)

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