Recent advances in the science and technology of ultra low sulfur diesel (ULSD) production

3.2. Preparation 4090 3.3. Intermediate Layers 4090 3.4. Support 4090 3.5. Modification 4091 3.5.1. Silica Membrane Modification 4091 3.5.2. Membrane Structure Modification 4092 3.6. Operational Stability 4092 4. Zeolite Membranes 4092 4.1. Membrane Growth Methods 4093 4.2. Permeation and Gas Transport 4093 4.3. Defect Site Diffusion/Nonzeolitic Pores 4094 4.4. Thin Films 4094 4.5. Zeolite Membrane Modification 4094 4.6. CO2 Sequestration in H2 Separations 4095 4.7. Manufacturing 4095 5. Carbon-Based Membranes 4096 5.1. Carbon Membrane Preparations 4097 5.2. Carbon Membrane Post-treatment 4097 5.3. Carbon Membrane Module Construction 4097 5.4. Selective Surface Flow Membranes 4097 5.5. Disadvantages of Carbon Membranes 4098 5.6. Molecular Sieving Carbon Membranes 4098 5.7. Carbon Nanotubes 4099 6. Polymer Membranes for H2 Separations 4100 6.1. Dense Polymeric Membranes 4100 6.2. Hydrogen Selective Polymeric Membranes 4101 6.3. H2 versus CO2 Selective Polymeric Membranes 4103

Membranes for hydrogen separation.

and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Nanoscaled metal borides and phosphides: recent developments and perspectives

Based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons, we present a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions. We show that the Seebeck coefficient can be significantly increased due to a strongly energy-dependent electronic scattering time. By including phonon scattering, we find that the enhancement of $ZT$ due to electron scattering is important for high doping, while at low doping it is primarily due to a decrease in the phonon thermal conductivity.

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Theory of enhancement of thermoelectric properties of materials with nanoinclusions.

$\text{La}B{\text{O}}_{3}$ ($B=\text{Mn}$, Fe, Co, and Ni) perovskites form a family of materials of significant interest for cathodes of solid oxide fuel cells (SOFCs). In this paper ab initio methods are used to study both bulk and surface properties of relevance for SOFCs, including vacancy formation and oxygen binding energies. A thermodynamic approach and the density functional theory plus $U$ method are combined to obtain energies relevant for SOFC conditions ($T\ensuremath{\approx}800\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, $P{\text{O}}_{2}\ensuremath{\approx}0.2\text{ }\text{atm}$). The impact of varying ${U}_{\text{eff}}$ $({U}_{\text{eff}}=U\ensuremath{-}J)$ on energy and electronic structure is explored in detail and it is shown that optimal ${U}_{\text{eff}}$ values yield significantly better agreement with experimental energies than ${U}_{\text{eff}}=0$ (which corresponds to the standard generalized gradient approximation). $\text{La}B{\text{O}}_{3}$ oxygen vacancy formation energies are predicted to be in the order $\text{Fe}g\text{Mn}g\text{Co}g\text{Ni}$ (where the largest implies most difficult to form a vacancy). It is shown that (001) $B{\text{O}}_{2}$ terminated surfaces have 1--2 eV lower vacancy formation energies and therefore far higher vacancy concentrations than the bulk. The stable surface species at low temperature are predicted to be the superoxide $\text{O}_{2}{}^{\ensuremath{-}}$ for $B=\text{Mn}$, Fe, Co and a peroxide $\text{O}_{2}{}^{2\ensuremath{-}}$ with a surface oxygen for $B=\text{Ni}$. Entropy effects are predicted to stabilize the monomer oxygen surface state for all $B$ cations at higher temperatures. Overall oxygen coverage of the (001) $B{\text{O}}_{2}$ surface is predicted to be quite low at SOFC operating conditions. These results will aid in understanding the oxygen reduction reaction on perovskite SOFC cathodes.

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Ab initio energetics of LaBO3(001) (B=Mn, Fe, Co, and Ni) for solid oxide fuel cell cathodes

Phase separation and antisite defects in the thermoelectric TiNiSn half-Heusler alloys

Novel approaches for the development of highly efficient thermoelectric materials capable of a direct conversion of heat into electricity, are being constantly investigated. TiNiSn based half-Heusler alloys exhibit a high thermoelectric potential for practical, renewable power generation applications. The main challenge of further enhancement of the thermoelectric efficiency of these alloys lies in the reduction of the associated high lattice thermal conductivity values without adversely affecting the electronic transport properties. The current manuscript theoretically investigates two possible routes for overcoming this limitation in TiNiSn alloys. On the one hand, the influence of nano-grained structure of TiNiSn on the electronic structure of the material is theoretically demonstrated. On the other hand, the potential for thermal conductivity reduction upon increasing the Ni fraction in the intermetallic TiNiSn compound via the formation of metallic TiNi2Sn nanoparticles is also shown. Using the applied approach, a useful route for optimizing both the electronic and thermal properties of half-Heusler TiNiSn, for practical thermoelectric applications, is demonstrated.

An ab initio study of the thermoelectric enhancement potential in nano-grained TiNiSn

In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the enhancement of the direct thermal to electrical thermoelectric efficiency of n-type PbTe by Na and Cl co-doping. We show that such co-doping is expected to enhance the thermoelectric efficiency by more than 17% compared to any of the previously reported lanthanum or iodine doped single-phase compositions, due to reduced lattice thermal conductivity values, originated by lattice disordering and mass/radii fluctuations in addition to improved carrier mobilities, originated by lower effective masses.

Enhancement of the thermoelectric properties of n-type PbTe by Na and Cl co-doping

In an attempt to reduce the reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of n-type Pb1−xTixTe alloys, with x values of up to 3%. A solubility limit of 0.5 at. % Ti in PbTe was identified, while beyond this composition, a precipitation of a TiTe2 phase was occurred. An impressive maximal dimensionless thermoelectric figure of merit ZT of ∼1.2 was obtained upon 0.1% Ti doping at 500 °C, indicating a ∼9% efficiency enhancement compared to an undoped PbTe. It is shown that generating a functionally graded material based on undoped PbTe as a low temperature segment and a 0.1% Ti doped PbTe as a high temperature segment has a potential to enhance the efficiency by ∼14% compared to the undoped sample.

David Fuks

Papers

Phase separation and antisite defects in the thermoelectric TiNiSn half-Heusler alloys

An ab initio study of the thermoelectric enhancement potential in nano-grained TiNiSn

Enhancement of the thermoelectric properties of n-type PbTe by Na and Cl co-doping

High thermoelectric potential of n-type Pb1−xTixTe alloys

TiNiSn half-Heusler crystals grown from metallic flux for thermoelectric applications