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

Band Structure of Semiconductors

Simultaneous effects of convective conditions and nanoparticles on peristaltic motion

The physics of mesoscopic electronic systems has been explored for more than 15 years. Mesoscopic phenomena in transport processes occur when the wavelength or the coherence length of the carriers becomes comparable to, or larger than, the sample dimensions. One striking result in this domain is the quantization of electrical conduction, observed in a quasi-one-dimensional constriction formed between reservoirs of two-dimensional electron gas. The conductance of this system is determined by the number of participating quantum states or ‘channels’ within the constriction; in the ideal case, each spin-degenerate channel contributes a quantized unit of 2e2/h to the electrical conductance. It has been speculated that similar behaviour should be observable for thermal transport in mesoscopic phonon systems. But experiments attempted in this regime have so far yielded inconclusive results. Here we report the observation of a quantized limiting value for the thermal conductance, Gth, in suspended insulating nanostructures at very low temperatures. The behaviour we observe is consistent with predictions for phonon transport in a ballistic, one-dimensional channel: at low temperatures, Gth approaches a maximum value of g0 = π2k 2BT/3h, the universal quantum of thermal conductance.

Measurement of the Quantum of Thermal Conductance

Magnetic heat pumps, refrigerators and energy conversion prototypes, with an operation based on the magnetocaloric effect, usually show a restriction in their frequency of operation to a few Hertz. In 2010 it was proposed to apply thermal switches to overcome this barrier. In this article thermal switches built with Ni-nanowire Peltier elements are presented and the performance of such elements is discussed on a theoretical and experimental basis. Finally an approximate estimate of the performance of a magnetic refrigerator of the types built up to present is compared to that of a magnetic refrigerator applying nanowire thermal switches.

http://thermagv.grenoble.cnrs.fr/keynote/SI_Egolf_Abstract.pdf

High-frequency magnetocaloric modules with heat gates operating with the Peltier effect

Influence of Light Waves on the Effective Electron Mass in Quantum Wells, Wires, Inversion Layers and Superlattices

An attempt is made in this paper to present a simple theoretical analysis of the thermoelectric power under strong magnetic quantization (TPM) in III–V, II–VI, PbTe/PbSnTe, strained layer and HgTe/CdTe superlattices (SLs) with graded interfaces and compare the same with that of the constituent materials by formulating the respective magneto dispersion laws, which in turn control all the transport properties through Bolzmann transport equation. It has been observed, taking GaAs/Ga 1− x Al x As, CdS/CdTe, PbTe/PbSnTe, InAs/GaSb and HgTe/CdTe with graded interfaces as examples, that the TPM exhibits oscillatory dependence with the inverse quantizing magnetic field due to the SdH and allied SL effects and increases with increasing inverse electron concentration in an oscillatory manner in all the cases. The nature of oscillation is totally band structure dependent and the width of the finite interface enhances the numerical values of the TPM for all the aforementioned SLs. The numerical values of the TPM in graded SLs are greater than that of the constituent materials. The theoretical results are in quantitative agreement with the experimental results as given elsewhere. The well-known expressions for the bulk specimens of wide-gap materials can also be obtained as special cases of our generalized analysis under certain limiting conditions. In addition, we have suggested the experimental methods of determining the Einstein relation for diffusivity–mobility ratio, the Debye screening length and carrier contribution to the elastic constants, respectively, for materials having arbitrary dispersion laws.

Simple theoretical analysis of the thermoelectric power under strong magnetic quantization in superlattices of non-parabolic semiconductors with graded interfaces

Influence of quantum confinement on the photoemission from superlattices of optoelectronic materials

The carrier contribution to the elastic constants in III–V, ternary and quaternary materials in the presence of light waves: Simplified theory, relative comparison and a suggestion for experimental determination

S. Pahari

Papers

Influence of Light Waves on the Effective Electron Mass in Quantum Wells, Wires, Inversion Layers and Superlattices

Simple theoretical analysis of the thermoelectric power under strong magnetic quantization in superlattices of non-parabolic semiconductors with graded interfaces

Influence of quantum confinement on the photoemission from superlattices of optoelectronic materials

The carrier contribution to the elastic constants in III–V, ternary and quaternary materials in the presence of light waves: Simplified theory, relative comparison and a suggestion for experimental determination

Simple Theoretical Analysis of the Photoemission from Quantum Confined Non-Linear Optical, Optoelectronic, and Related Materials