Mechanochemical synthesis of erbium borohydride: Polymorphism, thermal decomposition and hydrogen storage

A new erbium borohydride Er(BH4)3 was synthesized from 3LiBH4 and ErCl3 through mechanochemical processing. This rare-earth metal borohydride presents a primitive cubic structure with a = 10.74(1) Å, which is isostructural with the one previously reported for R(BH4)3 (R = Y, Dy and Gd). During heating Er(BH4)3 exhibits a reversible structural transformation at about 220 °C, analogous to that observed for Y(BH4)3. Combination of thermal hydrogen desorption, DSC, XRPD and FTIR measurements allows to determine that thermal decomposition of Er(BH4)3 starts at 230 °C and leads to 3.2 wt% of hydrogen release obtaining ErH2, an unknown intermediate compound and ErB4. It was observed that Er(BH4)3 is partially reversible under 6.0 MPa of H2 at 400 °C and absorbs about 20% of the total hydrogen capacity obtained experimentally.