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Abstract

Eutectic melting, reactive hydride composites, and nanoconfinement have the potential to improve the reversible hydrogen storage properties in metal borohydrides. We study and compare the combined effect of all three methods on reversible hydrogen release and uptake of the eutectic melting lithium potassium borohydride system, 0.725LiBH₄–0.275KBH₄, with low melting temperature (T_m = 105 °C). The eutectic mixture and reactive hydride composites of the eutectic mixture with Mg or MgH₂ are melt infiltrated into a CO₂ activated nanoporous carbon scaffold, and their properties are compared to those of bulk samples. The decomposition of 0.725LiBH₄–0.275KBH₄ and the reactive hydride composites initiates simultaneously with the melting at 105 °C, but the decomposition remains slow until higher temperatures are reached (T > 300 °C). Eutectic melting appears to improve kinetics of hydrogen release and absorption, while nanoconfinement lowers the main hydrogen release temperature in the first cycle by up to 200 °C. Temperature-programmed photographic analysis confirms the melting of the composites and shows frothing in the bulk samples. Thermogravimetric analysis and Sievert’s measurements are used to quantify the released gas, and the decomposition pathway is studied using in situ synchrotron radiation powder X-ray diffraction.