Hydrogen storage properties of rare earth (RE) borohydrides (RE = La, Er) in composite mixtures with LiBH₄ and LiH

Highlights: • 6LiBH₄–RECl₃–3LiH composites (RE = La, Er) studied for the first time. • Drastically reduced decomposition temperature (300 ^oC) compared to LiBH₄ (>400 °C). • Partial reversibility for 6LiBH₄–LaCl₃–3LiH: (19% at 340 °C, 10 MPa). • Excellent reversibility for 6LiBH₄–ErCl₃–3LiH: (80% at 340 °C, 10 MPa). • Reversibility comparable to that obtained for pure LiBH₄ (76% at 600 °C and 15.5 MPa). - Abstract: Mixtures of 6LiBH₄–RECl₃–3LiH (RE = La, Er) have been produced by mechanochemical milling and their structure, thermal decomposition and reversibility have been studied. Hydrogen desorption starts around 300 °C in both composites. Heating to 400 °C yields LaB₆, ErB₄ and REH_2+δ as major decomposition products. LiBH₄ is destabilized by REH_2+δ formed through decomposition of the parent borohydrides LiLa(BH₄)₃Cl and Er(BH₄)₃, respectively, and its hydrogen release temperature is reduced by 100 °C as compared to pure ball-milled LiBH₄. The lanthanum-containing composite releases 4.2 wt.% H between 300 and 350 °C and shows a limited reversibility of ∼20% (340 °C, 10 MPa) probably due to hydrogen uptake by some amorphous boron-containing phases. For 6LiBH₄–ErCl₃–3LiH about 3 wt.% H is evolved up to 400 °C. Desorption against 0.5 MPa backpressure results in an increased reversibility (∼80%) as compared to vacuum (∼66%). Rehydrogenation (340 °C, 10 MPa) shows the formation of ErH₃ and LiBH₄ at drastically reduced conditions compared to pure LiBH₄ (>400 °C, >10 MPa)