New mechanism and improved kinetics of hydrogen absorption and desorption of Mg(In) solid solution alloy milling with CeF3

Abstract

This paper presents improving the hydrogen absorption and desorption of Mg(In) solid solution alloy through doped with CeF3. A nanocomposite of Mg0.95In0.05-5 wt% CeF3 was prepared by mechanical ball milling. The microstructures were systematically investigated by X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy. And the hydrogen storage properties were evaluated by isothermal hydrogen absorption and desorption, and pressure-composition-isothermal measurements in a temperature range of 230 °C–320 °C. The mechanism of hydrogen absorption and desorption of Mg0.95In0.05 solid solution is changed by the addition of CeF3. Mg0.95In0.05-5 wt% CeF3 nanocomposite transforms to MgH2, MgF2 and intermetallic compounds of MgIn and CeIn3 by hydrogenation. Upon dehydrogenation, MgH2 reacts with the intermetallic compounds of MgIn and CeIn3 forming a pseudo-ternary Mg(In, Ce) solid solution, which is a fully reversible reaction with a reversible hydrogen capacity～4.0 wt%. The symbiotic nanostructured CeIn3 impedes the agglomeration of MgIn compound, thus improving the dispersibility of element In, and finally improving the reversibility of hydrogen absorption and desorption of Mg(In) solution alloy. For Mg0.95In0.05-5 wt% CeF3 nanocomposite, the dehydriding enthalpy is reduced to about 66.1 ± 3.2 kJ⋅mol−1⋅H2, and the apparent activation energy of dehydrogenation is significantly lowered to 71.9 ± 10.0 kJ⋅mol−1⋅H2, a reduction of ～73 kJ⋅mol−1⋅H2 relative to that for Mg0.95In0.05 solid solution. As a result, Mg0.95In0.05-5 wt% CeF3 nanocomposite can release ～57% H2 in 10 min at 260 °C. The improvements of hydrogen absorption and desorption properties are mainly attributed to the reversible phase transition of Mg(In, Ce) solid solution combing with the multiphase nanostructure.