The continuing depletion of many energy resources requires the development of research to replace them. In order to solve the global issue, this study applied carbon nanomaterials to energy conversion and storage devices. Chapter 1 describes the overall carbon materials and their applications. In Ch...
The continuing depletion of many energy resources requires the development of research to replace them. In order to solve the global issue, this study applied carbon nanomaterials to energy conversion and storage devices. Chapter 1 describes the overall carbon materials and their applications. In Chapters 2 and 3, the applications of thermoelectric materials, one of the energy conversion devices, were used to improve the thermoelectric properties of bismuth antimony telluride (BST) and tungsten disulfide (WS2) using single-walled carbon nanohorns (SWCNH). Chapters 4 and 5 confirmed the potential of supercapacitors as energy storage devices using sulfur-doped carbon nanotubes and graphene oxide with SWCNH.
Chapter 2, BST, which was commercialized as thermoelectric materials for application in the low temperature range of less than 500 K, has been most actively researched. Among the various methods for increasing the thermoelectric performance of BST, an approach of improving the power factor by adjusting the electric conductivity and the Seebeck coefficient has been proposed. The carbon nanomaterials with excellent electrical conductivity to enhance the power factor can be expected to realize the excellent thermoelectric performance by controlling carrier concentration and carrier mobility. Among these carbon nanomaterials, SWCNH with spherical cluster shape of approximately 100 nm diameter have high dispersibility in various solvents and matrix materials, which is advantageous for manufacturing composites and improving electrical characteristic. In this chapter, in order to improve the thermoelectric effect of BST, the SWCNH nanoparticles were mechanically mixed with BST using the high frequency induction heated sintering system (HFIHS). The electrical conductivity, Seebeck coefficient, and power factor values were obtained using for terminal mode (ZEM-3 equipment) at 300-400 K. The highest power factor (3.96 mW m-1K-2) was obtained from the BST-SWCNH composites with content of 0.5 wt% SWCNH, which was 1.4 times higher than that of pure BST (2.83 mW m-1K-2). the use of nanostructured SWCNH filler improved the electrical properties, and thereby enhanced the thermoelectric effect.
Chapter 3, thermoelectric materials have many limitations in terms of scarcity and commercial viability. Of the thermoelectric materials, WS2 is not only advantageous in terms of scarcity commerciality, but also can be used as a next generation thermoelectric materials because it has a high Seebeck coefficient. However, since the electric conductivity is low, it is limited as a thermoelectric materials. In order to overcome this problem, we investigated WS2-SWCNH composites prepared by powder metallurgy. The thermoelectric properties were observed by increasing the content of SWCNH from 0 to 1 wt%. The WS2-SWCNH mixture was sintered by HFIHS in a vacuum (10-3 torr). We invested thermoelectric performance of WS2-SWCNH composites. The inclusion of a small content of SWCNH (0.1 wt%) was dramatically increased electrical conductivity (by 126%) with a moderate decrease in the Seebeck coefficient (by 6%) and a slightly increase in thermal conductivity (by 23%) improving both power factor and thermoelectric figure of merit at 780 K. Therefore, the possibility of SWCNH as a thermoelectric material additive was confirmed by analysis of WS2-SWCNH composites according to temperature and composition of SWCNH.
Chapter 4, S-doped carbon nanotubes (S-CNTs) were successfully synthesized by chemical vapor deposition (CVD) using Fe/zeolite as catalyst and dimethyl disulfide (C2H6S2) as carbon source, and followed by purification (P-S-CNTs). The P-S-CNTs with a diameter of 30–50 nanometers contained 1.74 wt% S. In order to confirm the S-doping effects, the doped S atoms were partially removed from P-S-CNTs by heat-treatment in H2 atmosphere (De-P-S-CNTs). Commercial activated carbon (MSP20) was used as active material, and commercial conducting agent (Super-P), commercial multi-walled CNTs (MWCNTs), and De-P-S-CNTs as well as P-S-CNTs were used as conducting materials of supercapacitor electrodes using organic electrolyte. The electrode with P-S-CNTs exhibited the highest specific capacitance at high discharge current density of 100 mA cm–2 (120.18 F g–1) and the lowest charge transfer resistance (6.19 Ω), which are far superior to those of Super-P (83.88 F g–1 and 15.16 Ω), MWCNTs (87.82 F g–1 and 17.02 Ω), and De-P-S-CNTs (90.05 F g–1 and 22.33 Ω). Furthermore, the P-S-CNTs as active material exhibited superior electrochemical performance compared to MWCNTs. The superior electrochemical performance of P-S-CNTs is attributed to excellent electrical conductivity due to the S-doping effect.
Chapter 5, the Ni/Co layered double hydroxide (LDH) material has received considerable attention as an excellent pseudocapacitor materials. A facile method of directly growing LDH hybrid hierarchical nanostructures on synthesis of highly densified carbon materials was developed by a hydrothermal method. To prepare the highly densified carbon materials, we successfully synthesized graphene and HNO3-treatment of SWCNH (NH) using spray drying method in heat air. During the synthesis process, NH played a pivotal role in dense spherical structure through quickly solvent evaporate into GOs and NH and well dispersed GO sheets wrap around the NH. The electrochemical activity of the LDH/spray-dried GOs-NH (M/SGO-NH) was evaluated by cyclic voltammetry (CV), cycle retentions, and electrochemical impedance spectroscopy (EIS). In comparison with the LDH/spray-dried GOs (M/SGO), M/SGO-NH exhibited the highest gravimetric specific capacitance of 1046 F g-1 at 1 mV s-1, desirable rate stability at 10 mV s-1 (82% retention after 1,000 cycles), and low charge transfer resistance (3.47 Ω) in the high frequency range of the Nyquist plot in a conventional three electrode cell in 6 M KOH. Due to fast ion and electron transfer and large reaction surface area, M/SGO-NH electrodes with pseudocapacitive and high densified hybrid nanostructures can be substituted energy storage devices, such as pseudocapacitors.
The continuing depletion of many energy resources requires the development of research to replace them. In order to solve the global issue, this study applied carbon nanomaterials to energy conversion and storage devices. Chapter 1 describes the overall carbon materials and their applications. In Chapters 2 and 3, the applications of thermoelectric materials, one of the energy conversion devices, were used to improve the thermoelectric properties of bismuth antimony telluride (BST) and tungsten disulfide (WS2) using single-walled carbon nanohorns (SWCNH). Chapters 4 and 5 confirmed the potential of supercapacitors as energy storage devices using sulfur-doped carbon nanotubes and graphene oxide with SWCNH.
Chapter 2, BST, which was commercialized as thermoelectric materials for application in the low temperature range of less than 500 K, has been most actively researched. Among the various methods for increasing the thermoelectric performance of BST, an approach of improving the power factor by adjusting the electric conductivity and the Seebeck coefficient has been proposed. The carbon nanomaterials with excellent electrical conductivity to enhance the power factor can be expected to realize the excellent thermoelectric performance by controlling carrier concentration and carrier mobility. Among these carbon nanomaterials, SWCNH with spherical cluster shape of approximately 100 nm diameter have high dispersibility in various solvents and matrix materials, which is advantageous for manufacturing composites and improving electrical characteristic. In this chapter, in order to improve the thermoelectric effect of BST, the SWCNH nanoparticles were mechanically mixed with BST using the high frequency induction heated sintering system (HFIHS). The electrical conductivity, Seebeck coefficient, and power factor values were obtained using for terminal mode (ZEM-3 equipment) at 300-400 K. The highest power factor (3.96 mW m-1K-2) was obtained from the BST-SWCNH composites with content of 0.5 wt% SWCNH, which was 1.4 times higher than that of pure BST (2.83 mW m-1K-2). the use of nanostructured SWCNH filler improved the electrical properties, and thereby enhanced the thermoelectric effect.
Chapter 3, thermoelectric materials have many limitations in terms of scarcity and commercial viability. Of the thermoelectric materials, WS2 is not only advantageous in terms of scarcity commerciality, but also can be used as a next generation thermoelectric materials because it has a high Seebeck coefficient. However, since the electric conductivity is low, it is limited as a thermoelectric materials. In order to overcome this problem, we investigated WS2-SWCNH composites prepared by powder metallurgy. The thermoelectric properties were observed by increasing the content of SWCNH from 0 to 1 wt%. The WS2-SWCNH mixture was sintered by HFIHS in a vacuum (10-3 torr). We invested thermoelectric performance of WS2-SWCNH composites. The inclusion of a small content of SWCNH (0.1 wt%) was dramatically increased electrical conductivity (by 126%) with a moderate decrease in the Seebeck coefficient (by 6%) and a slightly increase in thermal conductivity (by 23%) improving both power factor and thermoelectric figure of merit at 780 K. Therefore, the possibility of SWCNH as a thermoelectric material additive was confirmed by analysis of WS2-SWCNH composites according to temperature and composition of SWCNH.
Chapter 4, S-doped carbon nanotubes (S-CNTs) were successfully synthesized by chemical vapor deposition (CVD) using Fe/zeolite as catalyst and dimethyl disulfide (C2H6S2) as carbon source, and followed by purification (P-S-CNTs). The P-S-CNTs with a diameter of 30–50 nanometers contained 1.74 wt% S. In order to confirm the S-doping effects, the doped S atoms were partially removed from P-S-CNTs by heat-treatment in H2 atmosphere (De-P-S-CNTs). Commercial activated carbon (MSP20) was used as active material, and commercial conducting agent (Super-P), commercial multi-walled CNTs (MWCNTs), and De-P-S-CNTs as well as P-S-CNTs were used as conducting materials of supercapacitor electrodes using organic electrolyte. The electrode with P-S-CNTs exhibited the highest specific capacitance at high discharge current density of 100 mA cm–2 (120.18 F g–1) and the lowest charge transfer resistance (6.19 Ω), which are far superior to those of Super-P (83.88 F g–1 and 15.16 Ω), MWCNTs (87.82 F g–1 and 17.02 Ω), and De-P-S-CNTs (90.05 F g–1 and 22.33 Ω). Furthermore, the P-S-CNTs as active material exhibited superior electrochemical performance compared to MWCNTs. The superior electrochemical performance of P-S-CNTs is attributed to excellent electrical conductivity due to the S-doping effect.
Chapter 5, the Ni/Co layered double hydroxide (LDH) material has received considerable attention as an excellent pseudocapacitor materials. A facile method of directly growing LDH hybrid hierarchical nanostructures on synthesis of highly densified carbon materials was developed by a hydrothermal method. To prepare the highly densified carbon materials, we successfully synthesized graphene and HNO3-treatment of SWCNH (NH) using spray drying method in heat air. During the synthesis process, NH played a pivotal role in dense spherical structure through quickly solvent evaporate into GOs and NH and well dispersed GO sheets wrap around the NH. The electrochemical activity of the LDH/spray-dried GOs-NH (M/SGO-NH) was evaluated by cyclic voltammetry (CV), cycle retentions, and electrochemical impedance spectroscopy (EIS). In comparison with the LDH/spray-dried GOs (M/SGO), M/SGO-NH exhibited the highest gravimetric specific capacitance of 1046 F g-1 at 1 mV s-1, desirable rate stability at 10 mV s-1 (82% retention after 1,000 cycles), and low charge transfer resistance (3.47 Ω) in the high frequency range of the Nyquist plot in a conventional three electrode cell in 6 M KOH. Due to fast ion and electron transfer and large reaction surface area, M/SGO-NH electrodes with pseudocapacitive and high densified hybrid nanostructures can be substituted energy storage devices, such as pseudocapacitors.
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#Carbon nanomaterials Thermoelectric materials Supercapacitor
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