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

• Published in: Journal of composites science Vol. 4; no. 1; p. 14
• Main Authors: Beate Krause, Ioannis Konidakis, Mohammad Arjmand, Uttandaraman Sundararaj, Robert Fuge, Marco Liebscher, Silke Hampel, Maxim Klaus, Efthymis Serpetzoglou, Emmanuel Stratakis, Petra Pötschke
• Format: Journal Article
• Language: English
• Published: MDPI AG 2020
• Subjects: carbon nanotube; nitrogen doping; polypropylene; thermoelectric
• ISSN: 2504-477X
• DOI: 10.3390/jcs4010014

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.