N-type thermoelectric textile fabrics based on vapor grown carbon nanofibers

Thermoelectric (TE) devices that convert a heat gradient directly into electricity are considered as a clean technology for energy harvesting. Both hole-transporting (p-type) and electron-transporting (n-type) materials are required in order to fabricate a thermoelectric module. Carbon nanotube (CNT)-based textile fabrics are relevant in this context for the production of wearable TE modules due to the combination of the high electrical conductivity and thermopower (Seebeck coefficient) from the CNT and the low thermal conductivity and flexibility provided by the textile fabric [1]. Nevertheless, most as-produced CNTs are p-type materials due to their inherent oxygen doping, and therefore the production of air- and thermally stable n-type CNT-based textile fabrics remains a challenge nowadays [2]. On the other hand, vapor-grown carbon nanofibers (VGCNF), produced by chemical vapor deposition (CVD), have similar structures to multiwall carbon nanotubes (MWCNT), which make them valuable for electronic applications. For instance, by adjusting process variables during their CVD and post-growth heat treatment, VGCNF can be tailored to have a wide range of thermal conductivity and electrical conductivity at room temperature. In particular, the unexpected n-type character at room temperature that they supply to dip-coated cotton fabrics will be the issue of this presentation [3]

Lifetime assessment of solid-state hybrid supercapacitors based on cotton fabric electrodes

Electrodes based on activated carbon and manganese oxide coated on a cotton woven fabric were developed and investigated. The electrodes were then assembled with two polymer electrolyte membranes, Nafion®115 and Aquivion®E87-05S, and two different supercapacitors were produced with specific capacitances and energy densities of 130 and 132 F g−1, and 11.5 and 11.7 Wh kg−1, respectively. Furthermore, a new durability methodology, which combines galvanostatic charge/discharge cycles together with potentiostatic floating conditions, was used to get insight into their electrochemical performance under stringent conditions. The supercapacitor assembled with Nafion®115 electrolyte worked successfully for 10 k cycles and 140 h under a constant voltage of 1.6 V (floating condition), whereas the supercapacitor assembled with Aquivion®E87-05S electrolyte worked successfully for more than 15 k cycles and 210 h, without any appreciable degradation of their electrochemical properties. In summary, hybrid solid-state supercapacitors based on electrodes produced by simple methodologies and low-cost materials, and with long durability performance under very harsh conditions were developed and analysed for their potential utilization as flexible energy storage devices.This work was supported by Project UID/CTM/00264/2019 of 2C2T – Centro de Ciência e Tecnologia Têxtil, funded by National Founds through FCT/MCTES. This research was also partially supported by the Cost Action 15107, Grant No. ECOST-STSM-CA15107-300118-092731

Solid-state carbon-based textile supercapacitors for energy storage applications

In this work, carbon-based conducting electrodes based on two different types of carbon nanofibers (CNF) have been produced by the dip and dry coating method onto cotton substrates. Furthermore, activated carbon (Norit A Supra Eur) and manganese oxide (MnO2) have been subsequenlty added to the CNF-based dip-coated cotton fabrics electrodes and asymmetric supercapacitors have been constructed and tested with the focus of obtaining devices with increased capacitive performance. In particular, the carbon-based active layer was prepared by spreading on the CNF-based electrodes a slurry containing the activated carbon (AC) material, graphite fibres, polyvinylidene difluoride (PVDF) as binder and N,N dimethylacetamide (DMA) solvent, whereas the MnO2 based active layer was prepared by spreading on the CNF-based textile electrodes a slurry formed by MnO2, carbon black, graphite fibers, PVDF and DMA. A solution of 1M Na2SO4 impregnated in porous paper separator (Nippon Kodoshi Corportion, Japan) was employed as neutral aqueous electrolyte. The supercapacitors were electrochemical investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results indicated that with this particular combination of carbon and manganese oxide active layers on CNF-based cotton fabrics it was possible to obtain specific capacitance of 100 F/g and a high specific energy density of 10 Wh/kg.This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007136. A. J. Paleo acknowledges the support of COST Action CA15107- Multi-Functional Nano-Carbon Composite Materials Network (MultiComp) by means of a short term scientific mission (STSM).info:eu-repo/semantics/publishedVersio

Carbon and MnO₂ materials on carbon nanofibers cotton textile substrate for hybrid solid-state supercapacitors

This work is focused on the design and development of hybrid solid-state energy storage devices with high capacitive performance. In particular, the work includes, the preparation of carbon composite electrodes based on a carbon nanofibers (CNF) supported on a cotton fabric. The coating of CNF to the cotton cloth is obtained by the dip and dry method. On these so-obtained composite substrates, further layers of activated carbon (Norit A Supra Eur) and manganese oxide (MnO2) material have been subsequenlty deposited to enhance the electrochemical performances of negative and positive electrodes, respectively. The preparation of carbon-based active layers comprises the spreading on the negative CNF-substrate of a slurry containing the activated carbon (AC) material, graphite fibres and polyvinylidene difluoride (PVDF) in N,N dimethylacetamide (DMA). Whereas the positive electrode is prepared by spreading a slurry of MnO2, carbon black, graphite fibers, PVDF in DMA. A 1M Na2SO4 solution impregnated in the porous paper separator (Nippon Kodoshi Corportion, Japan) and a polymer electrolyte membrane (Nafion 115) have been employed as electrolytes. The different supercapacitors were electrochemically characterized by cyclic voltammetry (CV), galvanostatic charge/discharge (G–CD), electrochemical impedance spectroscopy (EIS) and long-term cycling stability tests. The hybrid carbon-based textile supercapacitors exhibited capacitance performance of 137 and 120 F/g with the porous separator and Nafion 115 membrane, respectively. Specially, the solid-state (Nafion membrane) hybrid device demonstrated very long stability in cycling (10000 cycles) and holding voltage condition at 1.6 V (more than 100 h). Besides, these textile-based capacitors also showed slow self-discharge.This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology (project POCI-01-0145-FEDER-007136). A. J. Paleo acknowledges the European COST Action CA15107- Multi-Functional Nano-Carbon Composite Materials Network (MultiComp) that conceded a Short Term Scientific Mission (STSM) at CNR-ITAE of Messina.info:eu-repo/semantics/publishedVersio

Development of carbon/MnO₂ coated on nanofiber textile electrodes for hybrid solid-state supercapacitors

This work is focused on the design and development of hybrid solid-state energy storage devices with high capacitive performance. In particular, the work includes, the preparation of carbon composite electrodes based on a carbon nanofibers (CNF) supported on a cotton fabric. The coating of CNF to the cotton cloth is obtained by the dip and dry method. On these so-obtained composite substrates, further layers of activated carbon (Norit A Supra Eur) and manganese oxide (MnO2) material have been subsequenlty deposited to enhance the electrochemical performances of negative and positive electrodes, respectively. The preparation of carbon-based active layers comprises the spreading on the negative CNF-substrate of a slurry containing the activated carbon (AC) material, graphite fibres and polyvinylidene difluoride (PVDF) in N,N dimethylacetamide (DMA). Whereas the positive electrode is prepared by spreading a slurry of MnO2, carbon black, graphite fibers, PVDF in DMA. A 1M Na2SO4 solution impregnated in the porous paper separator (Nippon Kodoshi Corportion, Japan) and a polymer electrolyte membrane (Nafion 115) have been employed as electrolytes. The different supercapacitors were electrochemically characterized by cyclic voltammetry (CV), galvanostatic charge/discharge (G–CD), electrochemical impedance spectroscopy (EIS) and long-term cycling stability tests. The hybrid carbon-based textile supercapacitors exhibited capacitance performance of 137 and 120 F/g with the porous separator and Nafion 115 membrane, respectively. Specially, the solid-state (Nafion membrane) hybrid device demonstrated very long stability in cycling (10000 cycles) and holding voltage condition at 1.6 V (more than 200 h). Besides, these textile-based capacitors also showed really slow self-discharge.info:eu-repo/semantics/publishedVersio

Nonlinear thermopower behaviour of n-type carbon nanofibres and their melt mixed polypropylene composites

The temperature dependent electrical conductivity σ (T) and thermopower (Seebeck coefficient) S (T) from 303.15 K (30 °C) to 373.15 K (100 °C) of an as-received commercial n-type vapour grown carbon nanofibre (CNF) powder and its melt-mixed polypropylene (PP) composite with 5 wt.% of CNFs have been analysed. At 30 °C, the σ and S of the CNF powder are ~136 S m−1 and −5.1 μV K−1, respectively, whereas its PP/CNF composite showed lower conductivities and less negative S-values of ~15 S m−1 and −3.4 μV K−1, respectively. The σ (T) of both samples presents a dσ/dT S (T) shows a dS/dT > 0 character, also observed in some doped multiwall carbon nanotube (MWCNT) mats with nonlinear thermopower behaviour, and explained here from the contribution of impurities in the CNF structure such as oxygen and sulphur, which cause sharply varying and localized states at approximately 0.09 eV above their Fermi energy level (EF).Antonio J. Paleo gratefully acknowledges support from FCT-Foundation for Science and Technology by the “plurianual” 2020–2023 Project UIDB/00264/2020. E. Muñoz acknowledges support from Fondecyt grant number 1190361 and from ANID PIA Anillo ACT/192023

Dielectric relaxation of near-percolated carbon nanofiber polypropylene composites

In this work, the morphological, structural and dielectric analysis of near-percolated polypropylene (PP) com- posites containing carbon nano bers (CNF) processing by melt-mixing are investigated. Whereas the morpholog- ical analysis shows that CNF exhibit some tendency to agglomerate within the PP matrix, the structural analysis showed rst a general decrease in the intensity of the IR bands as a consequence of the interaction between carbon nano bers and PP matrix and second an increase of the crystallinity degree of the PP/CNF composites when compared to the pure PP. The dielectric analysis demonstrates enhanced dielectric constants (from 2.97 for neat polymer to 9.7 for 1.9 vol% loaded composites at 200 Hz) and low dielectric losses. Furthermore, the dielectric relaxation for composites with concentrations in the vicinity of percolation is evidenced and well de- scribed by the generalized polydispersive Cole-Cole model from which the values of static dielectric constant , high frequency dielectric constant , distribution of relaxation time (α) and mean relaxation time (τo ), are determined, suggesting that this latter analysis constitutes a strong tool for understanding the relationships between microstructure and dielectric properties in this type of polymer composites.This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT–Foundation for Science and Technology within the scope of the project POCI-01–0145-FEDER-007136. A. Ares-Pernas acknowledge the financial support to Xunta de Galicia-FEDER (Program of Consolidation and structuring competitive research units (GRC2014/ 036).info:eu-repo/semantics/acceptedVersio