Noble Metal Nanoparticles/Carbon Nanotubes Nanohybrids: Synthesis And Application In Electrocatalysis

As a new and very promising class of functional materials, noble metal nanoparticles/carbon nanotubes (CNTs) nanohybrids combine the advantages of noble metal nanoparticles (NPs) and CNTs, and show wide applications in electrocatalysis, heterogeneous catalysis and chemo/biosensing, especially in fuel cells. However, one of the most significant barriers for the widespread application of fuel cells is the high cost and limited resources of noble metal (Pt, Pd, Ru, etc.) electrocatalysts. Therefore, high dispersion and small particle size of noble metal NPs on CNT surface are desired not only from extraordinary catalytic activity but also from the low cost. In order to achieve this goal, surface functionalization of CNTs is generally carried out. However, during the fuctionalization process of CNTs, it is the key issue how to balance the conflicts between maintaining the original structure and properties of CNTs and introducing fuctional groups into CNTs. Developing efficient surface functionalization methods of CNTs is the urgent and key project to synthesize noble metal NPs/CNTs nanohybrids with high electrocatalytic performance.To solve the above problem, several methods for surface fuctionalization of CNTs have been developed. In this dissertation, taking the functionalized CNTs as support, noble metal NPs with high dispersion and small particle size have been supported on the CNTs surface. Additionally, the electrocatalytic properties of the prepared noble metal NPs/CNTs nanohybrids towards the electrooxidation of methanol, ethanol and formic acid have been studied in detail. The main points in this dissertation are summarized as follows:(1) Taking the 3, 4, 9, 10-perylene tetracarboxylic acid functionalized CNTs (CNTs-PTCA) as support, PtRu NPs with high dispersion and small particle size were successfully supported on CNT surface and the obtained PtRu/CNTs-PTCA nanohybrids were used as electrocatalysts for methanol oxidation. CNTs-PTCA was characterized by FTIR and Raman spectroscopy. The micrograph of PtRu/CNTs-PTCA nanohybrids and its electrocatalytic properties for methanol oxidation were characterized by transmission electron microscopy (TEM) and cyclic voltammetry (CV), respectively. The results show that CNTs-PTCA retain the structural of CNTs, PtRu NPs with an average diameter of ca. 2.8±0.5 nm are highly dispersed on the surface of CNTs-PTCA. Comparing PtRu/CNTs-AO catalysts, PtRu/CNTs-PTCA nanohybrids have much better electrocatalytic activity and stability towards methanol electrooxidation.(2) Using chitosan-functionalized CNTs (CNTs-Chit) as supporting materials, PtRu NPs with small particle size were uniformly deposited on the CNT surface and the obtained PtRu/CNTs-Chit nanohybrids were used as electrocatalysts for methanol oxidation. CNTs-Chit were characterized by thermal gravimertric analysis (TGA). The micrograph of PtRu/CNTs-Chit nanohybrids and its electrocatalytic properties for methanol oxidation were characterized by TEM and CV, respectively. The results show that the ratio of chitosan and CNTs in CNTs-Chit is 0.13:0.87. PtRu NPs with an average diameter of ca. 3.3±0.5 nm are highly dispersed on the CNTs-Chit surface. Comparing PtRu/CNTs nanohybrids, PtRu/CNTs-Chit nanohybrids possess much better electrocatalytic activity and long-term cycle stability toward methanol electrooxidation.(3) Ionic liquid polymer (PIL)-functionalized CNTs (CNTs-PIL) were synthesized via the thermal initiation free radical polymerization of IL monomer (1-vinyl-3-ethylimidazolium tetrafluoroborate, [VEIM]BF4). Pt and PtRu NPs with small particle size were uniformly dispersed on the CNT surface and the obtained Pt/CNTs-PIL and PtRu/CNTs-PIL nanohybrids were used as electrocatalysts for methanol oxidation. CNTs-PIL were characterized by TGA and Raman spectroscopy. The micrograph of Pt/CNTs-PIL and PtRu/CNTs-PIL nanohybrids and their electrocatalytic properties for methanol oxidation were characterized by TEM and CV, respectively. The results show that the PIL fuctionalization process of CNTs does not damage the structural of CNTs, and PtRu (Pt) nanoparticles with an average diameter of ca. 1.3±0.4nm (1.9±0.5nm for Pt) are highly dispersed on the CNTs-PIL surface. Comparing Pt/CNTs and PtRu/CNTs nanohybrids, Pt/CNTs-PIL and PtRu/CNTs-PIL nanohybrids have much better electrocatalytic performance towards methanol electrooxidation.(4) CNTs wrapped with nitrogen-doped carbon (CNX) layer (CNX@CNTs) were synthesized by carbonized CNTs-PIL. Using CNX@CNTs as support, PtRu NPs with high dispersion and small particle size were successfully supported on CNT surface and the obtained PtRu/CNX@CNTs nanohybrids were used as electrocatalysts for methanol oxidation. The CNX@CNTs was characterized by TEM, Raman spectroscopy and elemental analysis. The micrographs of PtRu/CNX@CNTs nanohybrids and its electrocatalytic properties for methanol oxidation were characterized by TEM and CV, respectively. The result show the CNTs surface was uniformly coated with a CNX layer with a thickness of ca. 1.5 nm, CNX@CNTs retain the structure of CNTs and the content of nitrogen element in CNX@CNTs is 0.35 wt.%. PtRu NPs with an average diameter of ca. 1.9±0.5 nm were highly dispersed on CNX@CNTs surface. Comparing PtRu/CNTs-AO catalysts, PtRu/CNX@CNTs catalysts have much better electrocatalytic activity and long-term stability toward methanol electrooxidation.(5) Taking CNTs-PIL as the support, PtSn NPs with high dispersion and small particle size were successfully supported on the CNT surface and the obtained PtSn/CNTs-PIL nanohybrids were used as the electrocatalysts for ethanol oxidation. The micrographs and elemental composition of PtSn/CNTs-PIL nanohybrids were characterized by TEM and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively. The electrocatalytic properties of PtSn/CNTs-PIL nanohybrids for ethanol oxidation were characterized by CV and chronoamperometry. The results show that comparing PtSn/CNTs nanohybrids, PtSn/CNTs-PIL nanohybrids have a better electrocatalytic performance for ethanol electrooxidation.(6) Using CNTs-PIL as the supporting material, PtPd NPs with high dispersion and small particle size were successfully supported on the CNT surface and the obtained PtPd/CNTs-PIL nanohybrids were used as the electrocatalysts for formic acid oxidation. The micrographs and elemental composition of the PtPd/CNTs-PIL nanohybrids were characterized by TEM and ICP-AES, respectively. The electrocatalytic properties of PtPd/CNTs-PIL nanohybrids for formic acid oxidation were characterized by CV and chronoamperometry. The results show that comparing PtPd/CNTs nanohybrids, PtSn/CNTs-PIL nanohybrids have much better electrocatalytic activity and long-term cycle stability towards formic acid electrooxidation.