Soluble alkali-metal carbon nanotube salts for n-type thermoelectric composites with improved stability

Dörling, Bernhard; Rodríguez‐Martínez, Xabier; Álvarez-Corzo, Ivan; Reparaz, J. S.; Campoy‐Quiles, Mariano

doi:10.1063/5.0047338

Cited by 13 publications

(19 citation statements)

References 37 publications

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“…To further investigate the final oxidation state after long-term aging, the time-dependence of the postaging TE properties was determined by completely immersing the sample in water for 28 days to deliberately induce an electrophilic reaction between the electron-activated sites and water molecules. 77 After 7 days, the σ value of 12-8-12/CNT increased from 2083 to 4564 S cm −1 (Figure 4B). This phenomenon cannot be fully explained by current models, although rinsing with water is considered to remove molecules from CNTs that interact as ions rather than covalently bonded molecules.…”

Section: Carbon Nanotube (Cnt)mentioning

confidence: 94%

Water‐resistant organic thermoelectric generator with >10 μW output

et al. 2022

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Flexible p–n thermoelectric generator (TEG) technology has rapidly advanced with power enhancement and size reduction. To achieve a stable power supply and highly efficient energy conversion, absolute chemical stability of n‐type materials is essential to ensuring large temperature differences between device terminals and ambient stability. With the aim of improving the long‐term stability of the n‐type operation of carbon nanotubes (CNTs) in air and water, this study uses cationic surfactants, such as octylene‐1,8‐bis(dimethyldodecylammonium bromide) (12–8–12), a gemini surfactant, to stabilize the nanotubes in a coating, which retains the n‐doped state for more than 28 days after exposure to air and water in experiments. TEGs with 10 p–n units of 12–8–12/CNT (n‐type) and sodium dodecylbenzene sulfonate/CNT (p‐type) layers are manufactured, and their water stability is evaluated. The initial maximum output of 16.1 µW (75 K temperature difference) is retained after water immersion for 40 days without using a sealant to prevent TEG module degradation. The excellent stability of these CNT‐based TEGs makes them suitable for underwater applications, such as battery‐free health monitoring and information gathering systems, and facilitates the development of soft electronics.

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Section: Carbon Nanotube (Cnt)mentioning

confidence: 94%

Water‐resistant organic thermoelectric generator with >10 μW output

et al. 2022

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“…More specifically, after approximately 30 d of aging, the σ values plateau until 120 d. The initial changes in the σ values were attributed to the adsorption of atmospheric oxygen. 53 Initially, the electrophilic reaction of oxygen on the CNT surfaces proceeds rapidly and then decelerates as the accessible active surface area decreases, subsequently resulting in a steady change in the level of doping. The n-type PF value of DTAB/CNT decreased from 219 to 126 μW m −1 K −2 after 30 d, retaining only 58% of the initial output characteristics.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…However, the σ values for these two samples show a decreasing trend with time. More specifically, after approximately 30 d of aging, the σ values plateau until 120 d. The initial changes in the σ values were attributed to the adsorption of atmospheric oxygen . Initially, the electrophilic reaction of oxygen on the CNT surfaces proceeds rapidly and then decelerates as the accessible active surface area decreases, subsequently resulting in a steady change in the level of doping.…”

Section: Results and Discussionmentioning

confidence: 99%

Surfactant-Wrapped n-Type Organic Thermoelectric Carbon Nanotubes for Long-Term Air Stability and Power Characteristics

Hata

Maeshiro

Shiraishi

et al. 2022

ACS Appl. Electron. Mater.

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The low air stability and unfavorable power properties of n-type carbon nanotubes (CNTs) limit the development of flexible electronics and organic transistors. Hence, determining an optimal n-dopant remains crucial. We propose the high surface coverage of adsorbed surfactant layers on nanotubes to maintain a continuous carrier stability and preserve the organic thermoelectric properties of n-type materials. Aqueous solutions of gemini surfactants with a tail length of 8 or 12 C atoms (8-3-8 and 12-3-12) were used as dispersants for the nanotubes. The gemini surfactants facilitated the enhanced dispersion of nanotubes to a greater degree than single-chain surfactants, ultimately improving the thermoelectric performance of films. An in-plane dimensionless figure-of-merit value of 6.04 × 10 −3 was recorded for the optimized 12-3-12/CNTs, which was comparable to that of oil-soluble dopants. In addition, the n-type thermoelectric characteristics had not been previously investigated beyond 100 d in conventional systems because of a significant drop in the power factor, which was caused by a decrease in the negative Seebeck coefficient. We therefore evaluated the air stabilities of CNTs fabricated using 8-3-8 and 12-3-12, observing that gemini surfactants extended the lifetimes and enhanced the thermoelectric performances of n-type carriers to a greater extent than single-chain surfactants. Approximately 83% of the initial power characteristics were retained for 12-3-12/CNTs after 120 d under air, which was attributed to the high surface area of the adsorbed gemini surfactant on the nanotubes. The low specific surface areas of the bare nanotubes reduced the oxygen-accessible area, suppressing hole doping caused by atmospheric oxygen and improving the stabilities and power characteristics of n-type CNTs. The future design of surfactants to control the form of cationic molecular adsorption is therefore essential to achieve sustained air stabilities and favorable output properties for n-type materials.

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“…Compared to 303 K, the electrophilic reaction of oxygen on the CNT surface was more rapid. 23 Nevertheless, the S values for all films confirmed the high air stability of surfactant/CNTs even under accelerated degradation conditions, with S values remaining consistently negative over time. The trend of the PF values was similar to that of σ values, except for P-C12/ CNT.…”

mentioning

confidence: 99%

“…Contrastingly, aging at 353 K gradually reduced the σ value of the three samples. Compared to 303 K, the electrophilic reaction of oxygen on the CNT surface was more rapid . Nevertheless, the S values for all films confirmed the high air stability of surfactant/CNTs even under accelerated degradation conditions, with S values remaining consistently negative over time.…”

mentioning

confidence: 99%

Long-Alkyl-Chain Phosphonium Surfactant Molecular Wrapping to Block Oxygen Impurities in n-Type Carbon Nanotubes for Thermoelectric Applications

Hata

Kitano

Ihara

et al. 2023

ACS Appl. Eng. Mater.

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In several electronics applications, the instability of components containing n-type carbon nanotubes (CNTs) to atmospheric oxidation in harsh environments or high temperatures is a significant concern. Here, we reported that a dense molecular wrapping of n-type CNTs with phosphonium salts reduced the exposed CNT surface by 79% and suppressed the electrophilic reaction of oxygen on the CNT surface. After aging at 353 K for 28 days, 89% of its initial thermoelectric power factor was retained (290.3 μW m–1 K–2). This opens new avenues for the use of n-type materials in high-temperature electronics.

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Soluble alkali-metal carbon nanotube salts for n-type thermoelectric composites with improved stability

Cited by 13 publications

References 37 publications

Water‐resistant organic thermoelectric generator with >10 μW output

Water‐resistant organic thermoelectric generator with >10 μW output

Surfactant-Wrapped n-Type Organic Thermoelectric Carbon Nanotubes for Long-Term Air Stability and Power Characteristics

Long-Alkyl-Chain Phosphonium Surfactant Molecular Wrapping to Block Oxygen Impurities in n-Type Carbon Nanotubes for Thermoelectric Applications

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