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Non-covalent polymer wrapping of carbon nanotubes and the role of wrapped polymers as functional dispersants

View Article: PubMed Central - PubMed

ABSTRACT

Carbon nanotubes (CNTs) have been recognized as a promising material in a wide range of applications from biotechnology to energy-related devices. However, the poor solubility in aqueous and organic solvents hindered the applications of CNTs. As studies have progressed, the methodology for CNT dispersion was established. In this methodology, the key issue is to covalently or non-covalently functionalize the surfaces of the CNTs with a dispersant. Among the various types of dispersions, polymer wrapping through non-covalent interactions is attractive in terms of the stability and homogeneity of the functionalization. Recently, by taking advantage of their stability, the wrapped-polymers have been utilized to support and/or reinforce the unique functionality of the CNTs, leading to the development of high-performance devices. In this review, various polymer wrapping approaches, together with the applications of the polymer-wrapped CNTs, are summarized.

No MeSH data available.


Schematic drawing of the two different approaches for Pt growth, namely the direct growth (upper) and PBI-assisted growth (lower) method.
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Figure 27: Schematic drawing of the two different approaches for Pt growth, namely the direct growth (upper) and PBI-assisted growth (lower) method.

Mentions: CNTs are recognized as an ideal supporting material for catalysts used in electrocatalysts, especially for fuel cells due to their higher electrical conductivities [311, 312], lower impurities [313] and higher electrochemical durability [314–318] compared to conventional supporting materials such as carbon blacks (CBs). However, due to the lack of binding sites, such as –COOH and –OH groups, loading of the metal catalyst onto the surfaces of pristine CNTs has been rather difficult. Therefore, the strong oxidation of the CNTs was carried out to introduce the hydrophilic groups [311, 313, 316, 317, 319–325]. However, since the oxidation is known to severely damage the graphitic structure of CNTs and damage the excellent electrochemical stability, a novel methodology to load the catalyst onto the non-oxidized CNTs has been required to utilize the intrinsic electrochemical stability of the pristine CNTs. In this issue, the introduction of binding sites by polymer wrapping of the pristine CNTs offers a promising solution. Until now, CNTs wrapped by poly(allylamine hydrochloride) [326, 327], chitosan [328], PANI [329–331], PDDA [332, 333] and PPy [331, 334, 335] were successfully used to anchor metal nanoparticles onto the surfaces of the pristine CNTs. In our group, PBI-wrapped pristine CNTs were used for the loading of Pt-nanoparticles (figure 27) [59, 60] in which imidazole units in PBI acted as the binding sites for Pt ions through a coordination mechanism, and quantitative loading of the Pt was achieved by a conventional polyol method using an ethylene glycol aqueous solution, H2PtCl6, as the reducing agent and Pt salt, respectively. The thus-obtained composite (CNT/PBI/Pt) was employed as the electrocatalyst in a polymer electrolyte fuel cell (PEFC) for the first time. As a result of the durability tests using the cells, it was revealed that the fuel cell using PBI-wrapped CNTs showed a remarkable durability compared to the conventional cell using the CB as the supporting material. In this strategy, since PBIs are known to have an excellent proton conductivity after acid doping [336], the wrapping layer of PBI also functioned to fabricate the proton conduction pathway along with CNT networks in the electrocatalyst.


Non-covalent polymer wrapping of carbon nanotubes and the role of wrapped polymers as functional dispersants
Schematic drawing of the two different approaches for Pt growth, namely the direct growth (upper) and PBI-assisted growth (lower) method.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036478&req=5

Figure 27: Schematic drawing of the two different approaches for Pt growth, namely the direct growth (upper) and PBI-assisted growth (lower) method.
Mentions: CNTs are recognized as an ideal supporting material for catalysts used in electrocatalysts, especially for fuel cells due to their higher electrical conductivities [311, 312], lower impurities [313] and higher electrochemical durability [314–318] compared to conventional supporting materials such as carbon blacks (CBs). However, due to the lack of binding sites, such as –COOH and –OH groups, loading of the metal catalyst onto the surfaces of pristine CNTs has been rather difficult. Therefore, the strong oxidation of the CNTs was carried out to introduce the hydrophilic groups [311, 313, 316, 317, 319–325]. However, since the oxidation is known to severely damage the graphitic structure of CNTs and damage the excellent electrochemical stability, a novel methodology to load the catalyst onto the non-oxidized CNTs has been required to utilize the intrinsic electrochemical stability of the pristine CNTs. In this issue, the introduction of binding sites by polymer wrapping of the pristine CNTs offers a promising solution. Until now, CNTs wrapped by poly(allylamine hydrochloride) [326, 327], chitosan [328], PANI [329–331], PDDA [332, 333] and PPy [331, 334, 335] were successfully used to anchor metal nanoparticles onto the surfaces of the pristine CNTs. In our group, PBI-wrapped pristine CNTs were used for the loading of Pt-nanoparticles (figure 27) [59, 60] in which imidazole units in PBI acted as the binding sites for Pt ions through a coordination mechanism, and quantitative loading of the Pt was achieved by a conventional polyol method using an ethylene glycol aqueous solution, H2PtCl6, as the reducing agent and Pt salt, respectively. The thus-obtained composite (CNT/PBI/Pt) was employed as the electrocatalyst in a polymer electrolyte fuel cell (PEFC) for the first time. As a result of the durability tests using the cells, it was revealed that the fuel cell using PBI-wrapped CNTs showed a remarkable durability compared to the conventional cell using the CB as the supporting material. In this strategy, since PBIs are known to have an excellent proton conductivity after acid doping [336], the wrapping layer of PBI also functioned to fabricate the proton conduction pathway along with CNT networks in the electrocatalyst.

View Article: PubMed Central - PubMed

ABSTRACT

Carbon nanotubes (CNTs) have been recognized as a promising material in a wide range of applications from biotechnology to energy-related devices. However, the poor solubility in aqueous and organic solvents hindered the applications of CNTs. As studies have progressed, the methodology for CNT dispersion was established. In this methodology, the key issue is to covalently or non-covalently functionalize the surfaces of the CNTs with a dispersant. Among the various types of dispersions, polymer wrapping through non-covalent interactions is attractive in terms of the stability and homogeneity of the functionalization. Recently, by taking advantage of their stability, the wrapped-polymers have been utilized to support and/or reinforce the unique functionality of the CNTs, leading to the development of high-performance devices. In this review, various polymer wrapping approaches, together with the applications of the polymer-wrapped CNTs, are summarized.

No MeSH data available.