Nitrogen-Doped Carbon Nanotube/Polypropylene Composites with Negative Seebeck Coefficient

Abstract

This study describes the application of multi-walled carbon nanotubes that were nitrogen-doped during their synthesis (N-MWCNTs) in melt-mixed polypropylene (PP) composites. Different types of N-MWCNTs, synthesized using different methods, were used and compared. Four of the five MWCNT grades showed negative Seebeck coefficients (S), indicating n-type charge carrier behavior. All prepared composites (with a concentration between 2 and 7.5 wt% N-MWCNTs) also showed negative S values, which in most cases had a higher negative value than the corresponding nanotubes. The S values achieved were between 1.0 μV/K and −13.8 μV/K for the N-MWCNT buckypapers or powders and between −4.7 μV/K and −22.8 μV/K for the corresponding composites. With a higher content of N-MWCNTs, the increase in electrical conductivity led to increasing values of the power factor (PF) despite the unstable behavior of the Seebeck coefficient. The highest power factor was achieved with 4 wt% N-MWCNT, where a suitable combination of high electrical conductivity and acceptable Seebeck coefficient led to a PF value of 6.1 × 10−3 µW/(m·K2). First experiments have shown that transient absorption spectroscopy (TAS) is a useful tool to study the carrier transfer process in CNTs in composites and to correlate it with the Seebeck coefficient.

Nanocomposites with p- and n-Type Conductivity Controlled by Type and Content of Nanotubes in Thermosets for Thermoelectric Applications

“…The three different kinds of lab-made nitrogen-doped MWCNTs show n-type behavior deduced from negative S values. This is in good agreement with other investigations of N-MWCNT reported in Krause et al [12,13].…”

“…Within CPCs, mainly thermoplastic matrices are currently considered, e.g., poly(vinylidene fluoride) (PVDF) [7], polypropylene (PP) [8][9][10][11][12][13][14] and polycarbonate [15][16][17]. Other polymers such as rubber, cellulose [18] or thermoset matrices (epoxy systems) have been studied less, or not at all.…”

“…Whereas multi walled CNTs (MWCNTs, namely Nanocyl NC7000 and Applied NanoStructured Solutions LLC CNS-PEG) always lead to p-type behavior, single walled CNTs (SWCNTs, namely OCSiAl Tuball 75% and Unidym HiPco super pure) resulted in certain polymer types, such as different polyamides (PAs) and acrylo butadiene styrene (ABS), in negative Seebeck coefficient values [12]. On the other hand, nitrogen doped MWCNTs always resulted in negative Seebeck values of their composites [12,13]. In these investigations on melt-mixed composites, performed with filler contents between 0.1 and 7.5 wt.…”

Carbon and carbon composites for thermoelectric applications

“…Then the melt-processed thermoplastics-based TE composites emerged from different research groups. [137][138][139][140][141] Pötschke et al [140][141][142][143][144][145][146] performed a series of TE research on melt-processed thermoplastics/CNT composites in terms of various aspects. They compared the effect of surface functionalization of MWCNT on the TE performance of melt-mixing polycarbonate (PC)/MWCNT at fixed MWCNT loading.…”

Preparation and Characterization of Electrically Conductive Polymer Nanocomposites with Different Carbon Nanoparticles

“…In addition to providing the ability to conduct heat and electricity since they can exhibit the Peltier and Seebeck effect, [23,24] such effects are beneficial in the development of thermoelectric materials, polymeric nanocomposites have also exhibited a noticeable improvement in mechanical properties, a barrier to gases, thermal stability [6,9,25,26] as well as the ability to modify the electrical properties of the host matrix to generate materials for capacitors, electromagnetic and/or radiofrequency shields, have even allowed the development of metamaterials capable of modifying their refractive index, dielectric constant and/or Seebeck effect [27][28][29].…”