Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

Recently a significant figure-of-merit (ZT) improvement in the most-studied existing thermoelectric materials has been achieved by creating nanograins and nanostructures in the grains using the combination of high-energy ball milling and a direct-current-induced hot-press process. Thermoelectric transport measurements, coupled with microstructure studies and theoretical modeling, show that the ZT improvement is the result of low lattice thermal conductivity due to the increased phonon scattering by grain boundaries and structural defects. In this article, the synthesis process and the relationship between the microstructures and the thermoelectric properties of the nanostructured thermoelectric bulk materials with an enhanced ZT value are reviewed. It is expected that the nanostructured materials described here will be useful for a variety of applications such as waste heat recovery, solar energy conversion, and environmentally friendly refrigeration.

Enhancement of Thermoelectric Figure-of-Merit by a Bulk Nanostructuring Approach

/pdf/nanostructured-thermoelectric-materials-current-research-and-4tijqszszy.pdf

Nanostructured thermoelectric materials: current research and future challenge

The phenomenal increase during the past decade in research utilizing pulsed electric current to activate sintering is attributed generally to the intrinsic advantages of the method relative to conventional sintering methods and to the observations of the enhanced properties of materials consolidated by this method. This review focuses on the fundamental aspects of the process, discussing the reported observations and simulation studies in terms of the basic aspects of the process and identifying the intrinsic benefits of the use of the parameters of current (and pulsing), pressure, and heating rate.

Electric Current Activation of Sintering: A Review of the Pulsed Electric Current Sintering Process

Materials for hydrogen-based energy storage – past, recent progress and future outlook

Rare earth–Mg–Ni-based hydrogen storage alloys as negative electrode materials for Ni/MH batteries

Thermoelectric Bi2Te3 nanotubes synthesized by low-temperature aqueous chemical method

A dramatic enhancement in the dehydrogenation/hydrogenation kinetics of Na2LiAlH6 was achieved by adding 5 wt% TiF4. The starting temperature for dehydrogenation of the sample with TiF4 added was lowered by 50 °C with respect to the pristine sample. In-depth investigations revealed that the addition of TiF4 to Na2LiAlH6 not only enhanced the dehydrogenation kinetics, but also altered the dehydrogenation thermodynamics. The apparent activation energy and the desorption enthalpy change of the Na2LiAlH6 with 5 wt% TiF4 added were calculated to be ca. 143.6 ± 2.7 kJ mol−1 and 57.3 ± 2.3 kJ mol−1 of H2 by using Kissinger's approach and the van't Hoff equation, both lower than those of the pristine sample, respectively. We firmly believe that both Ti and F play critical roles in the dehydrogenation/hydrogenation process of the Na2LiAlH6 sample with added TiF4 due to the formation of Ti–Al clusters, the substitution of F− for H− and the presence of LiF. All these are responsible for the significant improvement of hydrogen storage performances of the Na2LiAlH6 sample with the addition of TiF4. This understanding provides us with insights into the dehydrogenation kinetic mechanisms of Na2LiAlH6 used for hydrogen storage and directs the optimization of high-performance catalysts for the hydrogen storage reaction of the alanates.

Mechanisms for the enhanced hydrogen desorption performance of the TiF4-catalyzed Na2LiAlH6 used for hydrogen storage

Transition metal chalcogenides (TMCs) have been identified as pre‐electrocatalysts for the oxygen evolution reaction (OER) and the high valent TMs in the in situ generated oxyhydroxides are considered to be the real OER catalytic center. However, the role of chalcogens for OER process has been ignored and not fully elucidated. Herein, it is discovered that about 2.8–3.5% of chalcogens remain in as oxidized derivatives at a steady state, which plays a vital role for enhancing the catalytic activity. A facile and spontaneous sulfurizing method is developed to synthesize sulfur‐doped NiCo‐(oxy)hydroxysulfides (NCOSH) nanosheets, in which the sulfur can directly bond with high‐valence TMs and keep them stable for OER catalysis. Theoretical and experimental results suggest that the S‐coordination in NCOSH can cause bond length strengthening and electronic modulation between TM‐S and TM‐O, thus enhancing the oxidation activity and stability of high‐valence TMs in NCOSH. Consequently, the as‐obtained NCOSH exhibits superior bifunctional activities and durability for oxygen electrocatalytic reactions, and also serves as a superb air cathode in rechargeable solid state Zn‐air batteries. This work sheds light on the rational design of (oxy)hydroxysulfides as efficient electrocatalysts and gains deeper fundamental insights on the enhancing mechanism of S in oxyhydroxysulfides for diverse electrochemical applications.

Rational Design and Spontaneous Sulfurization of NiCo‐(oxy)Hydroxysulfides Nanosheets with Modulated Local Electronic Configuration for Enhancing Oxygen Electrocatalysis

Bulk thermoelectric materials are of interest for commercial application in both power generation and Peltier refrigeration. Various synthesis approaches have been developed by our group for high performance bulk thermoelectric materials, such as solvo- or hydrothermal synthesis for nanopowders, hot-pressing, and spark plasma sintering for nanostructured bulk materials, and rapid solidification for metal silicides. In this article we report some of our recent results in the development of high ZT thermoelectric materials, including Bi2Te3-Sb2Te3 nanocomposites and CoSb3 micro/nanocomposites prepared by a powder blending route, and GeTe-AgSbTe2 and Mg2Si-Mg2Sn nanocomposites prepared by an in situ route. The results show various possibilities for improved microstructures and therefore enhanced properties of bulk thermoelectric materials through optimization of the preparation processing based on simple synthesis routes. A high ZT of approximately 1.5 has been obtained in both Bi2Te3-Sb2Te3 and GeTe-AgSbTe2 nanocomposites. Further ZT enhancement of the materials should be possible through the control of the nanopowder morphology during synthesis and the hindering of␣grain growth during sintering, as well as through the optimization of composition and doping.

Yanhui Cao

Papers

Rare earth–Mg–Ni-based hydrogen storage alloys as negative electrode materials for Ni/MH batteries

Thermoelectric Bi2Te3 nanotubes synthesized by low-temperature aqueous chemical method

Mechanisms for the enhanced hydrogen desorption performance of the TiF4-catalyzed Na2LiAlH6 used for hydrogen storage

Rational Design and Spontaneous Sulfurization of NiCo‐(oxy)Hydroxysulfides Nanosheets with Modulated Local Electronic Configuration for Enhancing Oxygen Electrocatalysis

Synthesis of Nanocomposites with Improved Thermoelectric Properties