在聚光式太陽能高溫儲熱系統所使用的金屬氫化物材料中，氫化鎂(MgH2)是極具開發潛力的材料，其儲熱密度可達2257kJ/kg。本研究探討高溫下奈米過渡金屬Fe及Co對MgH2反應速率及循環穩定性的影響。研究發現在420oC，奈米添加物Fe、Co可有效提升MgH2之吸氫及放氫反應速率，但添加奈米Co之MgH2在循環反應後會有Mg2Co與Mg2CoH5的生成，造成循環穩定度不佳。在440℃僅添加奈米Co及Fe之MgH2產生吸放氫反應，添加奈米Fe之MgH2在循環反應後會有後Mg2FeH6的生成。非Ni之添加物(如奈米Fe)，或共晶溫度較高之添加物(如奈米Co)，雖可避免因Mg-Ni類型之共晶反應造成之鎂燒結，但仍可能因Mg與添加物之間生成之金屬間化合物以及Mg與添加物和氫化反應後生成之氫化物，導致循環反應速率與循環穩定度不佳。

Magnesium hydride (MgH2) is a promising high-temperature heat storage material for a concentrating solar thermal heat storage system. In the present work, the effects of nano-addtives, Fe and Co, on the high temperature sorption kinetics and cycle stability of MgH2 were studied. At 420 oC, the absorption/desorption kinetics of Mg/MgH2 can be significantly improved by adding 5 wt. % of nano-Fe or nano-Co as a catalyst；however, Mg2Coand Mg2CoH5 form during cycling of MgH2 with 5 wt. % of nano-Co, which results in unstable cycle performance. At 440 oC, MgH2 with 5 wt. % of nano-Co and nano-Fe react with hydrogen. It is also found that Mg and Fe react with hydrogen and form Mg2FeH6. Although the Mg-Ni type eutectic sintering can be avoided by using transition metal additive other than Ni, the formation of Mg-based intermetallic phases and the formation of ternary hydrides might happen for MgH2 doped with 5 wt. % of nano-Co or Fe, leading to a low reaction kinetics and unstable cycle performance.

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