Synthesis of CsH and its effect on the hydrogen storage properties of the Mg(NH2)2 2LiH system
Abstract Cesium hydride (CsH) was successfully synthesized by ball milling Cs under a hydrogen atmosphere of 50 bar at 50 degC. The effect of the prepared CsH on the hydrogen storage properties of the Mg(NH 2 2 2LiH system was systematically investigated. The Mg(NH 2 2 2LiH 0.08CsH composite exhibited optimal hydrogen storage properties because it reversibly stores approximately 4.62 wt% hydrogen with a dehydrogenation onset temperature of 70 degC via a two stage reaction. At 150 degC, approximately 80% of the reversible capacity was quickly released from the Mg(NH 2 2 2LiH 0.08CsH composite within 100 min. The fully dehydrogenated CsH containing sample began to absorb hydrogen at 55 degC and took up approximately 4.58 wt% hydrogen at 130 degC. A cycling analysis indicated that the CsH containing Mg(NH 2 2 2LiH system exhibited good reversible hydrogen storage abilities. Detailed mechanistic studies revealed that during the initial heating process, CsH gradually reacted with Mg(NH 2 2 to afford CsMg(NH)(NH 2 and CsH acted as a catalyst to reduce the activation energy barrier of the first dehydrogenation step. As the operating temperature increased, CsMg(NH)(NH 2 as a reactant participated in a second dehydrogenation step to decrease the desorption enthalpy change. This behavior reasonably explains the significantly improved hydrogen storage properties of the CsH containing Mg(NH 2 2 2LiH system.