Thermal and electrical transport properties in multi-walled carbon nanotube-coated ZnO tetrapods and self-entangled multi-walled carbon nanotube tubes

Abstract

We present the electrical and thermal properties of highly porous (∼94% porous) three-dimensional (3D) ZnO network structures coated with a thin layer of self-entangled multi-walled carbon nanotubes (MWCNTs), resulting in the formation of MWCNT microtubes (MWCNTTs) around the ceramic backbone. Additionally, we compare the properties of the composite (MWCNT/ZnO) structures to free-standing MWCNTTs, a hierarchical network consisting solely of randomly interconnected MWCNTs. The random 3D architecture of the ZnO network results in isotropic properties, in contrast to the typical one-dimensional (1D) properties of other CNT assemblies. The electrical conductivity of the MWCNT/ZnO composite increases with MWCNT content suggesting that MWCNTs are dominant over the entire temperature range. On the other hand, the thermal conductivity is mainly determined by the ceramic ZnO backbone at low temperature while the thermal conductivity of the MWCNTs is mainly dominant above 300 K. The electrical conductivity of the MWCNT/ZnO composites could reach values of up to 49 ± 2 S m−1 at room temperature whereas the room-temperature thermal conductivity of the MWCNTTs is 0.08 ± 0.02 W m−1 K−1. Direct comparison between both the composite and the pure MWCNTTs allows for a better understanding concerning which material in the composite dominates the transport properties.