New materials hold the key to fundamental advances in energy conversion and storage, both of which are vital in order to meet the challenge of global warming and the finite nature of fossil fuels. Nanomaterials in particular offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. This review describes some recent developments in the discovery of nanoelectrolytes and nanoelectrodes for lithium batteries, fuel cells and supercapacitors. The advantages and disadvantages of the nanoscale in materials design for such devices are highlighted.

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Nanostructured materials for advanced energy conversion and storage devices

Mobility — the transport of people and goods — is a socioeconomic reality that will surely increase in the coming years. It should be safe, economic and reasonably clean. Little energy needs to be expended to overcome potential energy changes, but a great deal is lost through friction (for cars about 10 kWh per 100 km) and low-efficiency energy conversion. Vehicles can be run either by connecting them to a continuous supply of energy or by storing energy on board. Hydrogen would be ideal as a synthetic fuel because it is lightweight, highly abundant and its oxidation product (water) is environmentally benign, but storage remains a problem. Here we present recent developments in the search for innovative materials with high hydrogen-storage capacity.

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Hydrogen-storage materials for mobile applications

The literature treating mechanisms of catalyst deactivation is reviewed. Intrinsic mechanisms of catalyst deactivation are many; nevertheless, they can be classified into six distinct types: (i) poisoning, (ii) fouling, (iii) thermal degradation, (iv) vapor compound formation accompanied by transport, (v) vapor-solid and/or solid-solid reactions, and (vi) attrition/crushing. As (i), (iv), and (v) are chemical in nature and (ii) and (v) are mechanical, the causes of deactivation are basically three-fold: chemical, mechanical and thermal. Each of these six mechanisms is defined and its features are illustrated by data and examples from the literature. The status of knowledge and needs for further work are also summarized for each type of deactivation mechanism. The development during the past two decades of more sophisticated surface spectroscopies and powerful computer technologies provides opportunities for obtaining substantially better understanding of deactivation mechanisms and building this understanding into comprehensive mathematical models that will enable more effective design and optimization of processes involving deactivating catalysts. © 2001 Elsevier Science B.V. All rights reserved.

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Mechanisms of catalyst deactivation

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

Carbon nanofibers (diameter range, 3–100 nm; length range, 0.1–1000 µm) have been known for a long time as a nuisance that often emerges during catalytic conversion of carbon-containing gases. The recent outburst of interest in these graphitic materials originates from their potential for unique applications as well as their chemical similarity to fullerenes and carbon nanotubes. In this review, we focus on the growth of nanofibers using metallic particles as a catalyst to precipitate the graphitic carbon. First, we summarize some of the earlier literature that has contributed greatly to understand the nucleation and growth of carbon nanofibers and nanotubes. Thereafter, we describe in detail recent progress to control the fiber surface structure, texture, and growth into mechanically strong agglomerates. It is argued that carbon nanofibers are unique high-surface-area materials (˜200 m2/g) that can expose exclusively either basal graphite planes or edge planes. Subsequently, we will present the recently ...

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Carbon Nanofibers: Catalytic Synthesis and Applications

The hydrogenation of ethylene, 1-butene, and 1,3-butadiene has been used as a probe reaction in an attempt to monitor any possible changes in catalytic behavior induced by supporting nickel on diff...

Catalytic Behavior of Graphite Nanofiber Supported Nickel Particles. 2. The Influence of the Nanofiber Structure

Hydrogen Storage in Graphite Nanofibers.

The understanding of the factors controlling the deposition of carbonaceous solids resulting from the decomposition of hydrocarbons over metal particles has a considerable impact on a number of commerical processes including: catalytic steam reforming of methane, catalytic reforming and systems involving carbon monoxide disproportionation reactions. The highest catalytic activity for carbon deposition is exhibited by iron, cobalt and nickel, and alloys containing these metals. During the past few years we have pursued a program designed to achieve conditions where it is possible to control the catalytic properties of a given metal by inducing perturbations to the reactive surfaces of the crystallites. One of the consequences of such an action is to enable one to alter the catalytic reactivity in such a fashion so as to optimize the performance for a desired reaction pathway, while simultaneously suppressing the rate of detrimental side reactions, such as encapsulating forms of carbon deposition. Our strategy has centered around a study of the effect of introducing selected adatoms into the host metal and using the decomposition of ethylene to probe the manner by which the chemistry of the various faces of the crytallites is modified. In this paper a discussion of the information obtained from the use of a combination of controlled atmosphere and high resolution transmission electron microscopy techniques to study the impact of metal particle morphology on the characteristics of the carbon deposit will be given.

The relationship between metal particle morphology and the structural characteristics of carbon deposits

We have used a variety of experimental techniques, including high-resolution transmission electron microscopy, X-ray diffraction, and adsorptive decomposition of N2O to examine the characteristics of copper particles dispersed on different types of graphite nanofiber supports. When copper was dispersed on the edge sites of graphite nanofibers the particles adopted a relatively thin faceted morphology; characteristics that are associated with the establishment of a strong metal−support interaction. This behavior is to be contrasted with that observed when the metal was supported on active carbon or the basal planes of graphite. In these cases, the particles tended to acquire a globular geometry typically encountered in systems were there are relatively weak interfacial forces between the metal and the support. Structural modeling of the arrangement of copper atoms on the prismatic and basal plane surfaces of graphite indicated that formation of preferred crystallite orientations occurred at certain support...

Characteristics of Copper Particles Supported on Various Types of Graphite Nanofibers

We have investigated the formation of graphite nanofibers from the catalytic decomposition of CO/H 2 mixtures over a series of powdered Fe-Cu catalysts at temperatures ranging from 500 to 700 °C. The physical and structural characteristics of the nanofibers have been established from examination of the materials by a variety of techniques including transmission electron microscopy, temperature-programmed oxidation, nitrogen surface area measurements, and X-ray diffraction. It was found that the addition of Cu to Fe did not exert a significant influence on the amount of solid carbon product formed in the reaction. On the other hand, examination of the nanofibers by high-resolution TEM revealed that the materials generated from Fe-rich Cu bimetallics were notably more graphitic in nature than those grown from pure Fe. As the reaction temperature was increased from 600 to 700 °C, the structure of the graphite nanofibers underwent a dramatic change from a "platelet" to "tubular" configuration. It is suggested that this transformation is directly associated with the α-Fe to γ-Fe phase change over this temperature range.

R. T. K. Baker

Papers

Catalytic Behavior of Graphite Nanofiber Supported Nickel Particles. 2. The Influence of the Nanofiber Structure

Hydrogen Storage in Graphite Nanofibers.

The relationship between metal particle morphology and the structural characteristics of carbon deposits

Characteristics of Copper Particles Supported on Various Types of Graphite Nanofibers

Growth of Graphite Nanofibers from the Iron−Copper Catalyzed Decomposition of CO/H2 Mixtures