The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.

Carbon nanotubes and nanofibers in catalysis

A review of anode catalysis in the direct methanol fuel cell

The unique and tunable properties of carbon-based nanomaterials enable new technologies for identifying and addressing environmental challenges. This review critically assesses the contributions of carbon-based nanomaterials to a broad range of environmental applications: sorbents, high-flux membranes, depth filters, antimicrobial agents, environmental sensors, renewable energy technologies, and pollution prevention strategies. In linking technological advance back to the physical, chemical, and electronic properties of carbonaceous nanomaterials, this article also outlines future opportunities for nanomaterial application in environmental systems.

Environmental applications of carbon-based nanomaterials.

It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size-/surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy-conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.

Carbon Nanomaterials for Advanced Energy Conversion and Storage

A higher yield of functionalized carbon nanotubes (CNTs) was obtained by treatment of CNTs in HNO3 or H2SO4−K2Cr2O7. The deposition of platinum nanoparticles and nanoclusters on these functionalized multiwalled carbon nanotubes by electroless plating was facilitated by a two-step sensitization-activation pretreatment. The deposition was sensitive to the aging time of the sensitizing solution and the pH of the plating solution. The resulting electrocatalysts were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. XPS analysis showed that the Pt/CNT electrocatalysts contained 67.3% of Pt(0) and 32.7% of Pt(IV). Test runs on a single stack polymer electrolyte membrane fuel cell showed that these electrocatalysts are very promising for fuel cell applications.

Preparation and characterization of platinum-based electrocatalysts on multiwalled carbon nanotubes for proton exchange membrane fuel cells

PtRu nanoparticles supported on Vulcan XC-72 carbon and carbon nanotubes were prepared by a microwave-assisted polyol process. The catalysts were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which were uniformly dispersed on carbon, were 2−6 nm in diameter. All PtRu/C catalysts prepared as such displayed the characteristic diffraction peaks of a Pt face-centered cubic structure, excepting that the 2θ values were shifted to slightly higher values. XPS analysis revealed that the catalysts contained mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV), and Ru(IV). The electro-oxidation of methanol was studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. It was found that both PtRu/C catalysts had high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a direct methanol fuel cell single stack test cell using the Vulcan...

Physical and Electrochemical Characterizations of Microwave-Assisted Polyol Preparation of Carbon-Supported PtRu Nanoparticles

Nanosized PtRu catalysts supported on carbon have been synthesized from inverse microemulsions and emulsions using H2PtCl6
(0.025 M)/RuCl3
(0.025 M)/NaOH (0.025 M) as the aqueous phase, cyclohexane as the oil phase, and NP5 (poly(oxyethylene)5 nonyl phenol ether) or NP9 (poly(oxyethylene)9 nonyl phenol) as the surfactant, in the presence of Carbon Black suspended in a mixture of cyclohexane and NP5 + NP9. The titration of 10% HCHO aqueous solution into the inverse microemulsions and emulsions resulted in PtRu/C catalysts, in which the PtRu particles were nanometers in size. The catalysts were characterized by TEM, XRD and XPS and the metal particles were found to inherit the Pt fcc structure with Pt and Ru mostly in the zero valence oxidation states, amidst some Pt(II), Pt(IV) and Ru(IV).
The cyclic voltammograms for methanol oxidation on these PtRu/C catalysts showed higher electrocatalytic activities for the two microemulsion derived catalysts than the emulsion-derived electrocatalyst.

Ming Han

Papers

Preparation and characterization of platinum-based electrocatalysts on multiwalled carbon nanotubes for proton exchange membrane fuel cells

Physical and Electrochemical Characterizations of Microwave-Assisted Polyol Preparation of Carbon-Supported PtRu Nanoparticles

Synthesis and characterization of PtRu/C catalysts from microemulsions and emulsions

Nano-TiO2-coated polymer electrolyte membranes for direct methanol fuel cells

The zwitterion effect in proton exchange membranes as synthesised by polymerisation of bicontinuous microemulsions