Hydrogen Storage Characteristics of Nanocrystalline and Amorphous Nd-Mg-Ni-Based NdMg 12 -Type Alloys Synthesized via Me
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INTRODUCTION
A greater dependence on fossil fuels, in conjunction with a rapid development of automobile industry, has caused an amazing growth in the rate of global warming. Developing alternative energies is an attractive strategy to reduce the use of fossil fuels. For transportation and vehicles, hydrogen, of all the available energies, is considered the most beneficial fuel that considers the convenience for transportation, versatility, utilization, efficiency, safety, and environmental compatibility.[1,2] Developing a practical hydrogen storage system has been proved to be a key technical obstacle for the realization of onboard fuel cell or hydrogen-fueled vehicles.[3] Among hydrogen storage methods, hydrogen storage in metal hydrides is considered one of the most promising alternatives to satisfy the requirements for mobile application.[4,5] Recently, extensive YANGHUAN ZHANG, Professor, and ZHONGHUI HOU, Doctoral Student, are with the Key Laboratory of Integrated Exploitation of Baiyun Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, 7 Aerding Avenue, Baotou 014010, P.R. China, and also with the Department of Functional Material Research, Central Iron and Steel Research Institute, 76 Xueyuannan Road, Beijing 100081, P.R. China. Contact e-mail: zhangyh59@ sina.com HONGWEI SHANG, ZEMING YUAN, TAI YANG, and YAN QI, Doctoral Students, are with the Department of Functional Material Research, Central Iron and Steel Research Institute. Manuscript submitted January 22, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
research has been performed to develop hydrogen storage mechanisms ground on different metal hydrides, and many hydrogen storage materials have been realizing the application goal. Unfortunately, none of these materials can satisfy all the performance requirements proposed by the U.S. Department of Energy for vehicular applications.[6,7] Concerning hydrogen absorption capacity, Mg-based alloys are considered promising candidates for hydrogen fuel cell vehicles.[8] Specifically, REMg12-type alloys have received increasing attention because of their gaseous hydrogen storage capacity within the range of 3.7 to 6.0 wt pct[9] and theoretical electrochemical capacity of over 1000 mAh/g,[10] which is much higher than that of Mg-Ni alloys. However, some inherent issues of Mg-based alloys, such as relatively high hydrogen desorption temperature, sluggish hydriding/dehydriding kinetics, and extremely low electrochemical discharge capacity at room temperature, severely hinder their practical application for hydrogen storage materials of vehicle-mounted fuel cell or negative electrode materials of Ni-MH batteries. Therefore, researchers in this area still face a serious challenge in further improving the hydrogen storage performance of Mg-based alloys. The proposed principles for enhancing the hydrogen storage performances of Mg-based alloys are classified into two categories: the first category is adding catalytic elements, such as transition metals, transition metal oxides, and rare-earth
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