Effect of the surface oxidation of LiBH4 on the hydrogen desorption mechanism

Abstract

The surface oxidation behavior of LiBH₄ and NaBH₄ was investigated in view of the formation and structure of the surface oxidation and its effect on the hydrogen desorption kinetics. The sample surfaces were intentionally modified by exposure to oxygen in the pressure range from 10⁻¹⁰ mbar up to 200 mbar. The induced surface changes were systematically studied by means of X-ray photoelectron spectroscopy. NaBH₄ shows a low reactivity with oxygen, while LiBH₄ oxidizes rapidly, accompanied by surface segregation of Li. The hydrogen desorption kinetics of LiBH₄ were studied by thermal desorption spectroscopy with particular emphasis on the analysis of the desorbed gases, i.e. diborane and hydrogen. The surface oxidation induces the formation of a Li₂O layer on LiBH₄, significantly reduces the desorption of diborane, and enhances the rate of hydrogen desorption.