Effects of triphenyl phosphate on the hydrogen storage performance of the Mg(NH2)2–2LiH system

Abstract

Mg(NH₂)₂–2LiH is an attractive system because of its high reversible hydrogen capacity (∼5.6 wt%) and suitable thermodynamic parameters that allow operation below 100 °C. However, a relatively high kinetic barrier in the hydrogen desorption blocks its application at low temperature. In this work, a small amount of additive, triphenyl phosphate (TPP), was introduced and its effects on hydrogen desorption/absorption in the Mg(NH₂)₂–2LiH system were studied. Experimental results showed that TPP can prevent aggregation/crystallization during the cycling tests and thus achieve an enhanced kinetic performance. Complete dehydrogenation and hydrogenation can be successfully carried out at temperatures below 150 °C. Moreover, a significant reduction of the entropy change of hydrogen desorption (ΔS_des) was found in the TPP-doped system compared with the pristine Mg(NH₂)₂–2LiH system, thought to be due to the persistence of amorphous Mg(NH₂)₂ in the TPP-doped sample during dehydrogenation and hydrogenation cycling, thereby greatly affecting the equilibrium hydrogen pressure.