Hydrogen storage and release: Kinetic and thermodynamic studies of MgH2 activated by transition metal nanoparticles

• The presence of Ni, Fe, and Co improves the hydrogen diffusion into the MgH2 matrix.
• MgH2–Ni sample shows the lowest activation energy and H2 desorption temperature.
• Zn and Cu nanoparticles are acting more like inhibitors than activators of MgH2.
• No new phases are formed after H2 absorption/desorption cycles of MgH2–Ni, Fe, Co.

Commercial metal nanoparticles of Fe, Co, Ni, Cu, Zn were added to MgH2 by ball-milling to improve the kinetics of hydrogen release and the reversibility during successive absorption/desorption cycles. metal nanoparticles were well dispersed into the MgH2 matrix without formation of any ternary metal hydrides, nor binary compounds. Activation energy values were determined for the various samples by temperature programmed desorption experiments while the hydride formation enthalpy was deduced from Van't Hoff equation starting from high pressure volumetric isotherms acquired at different temperatures. The presence of transient effect during the absorption process was excluded by comparing successive hydrogenation/dehydrogenation cycles recorded at 350 °C on Ni and Fe-containing samples. Information about hydrogen absorption kinetics was also obtained. Promisingly, the Ni, Fe, and Co containing samples have shown a good stability, enhanced catalytic performance, and high rate of hydrogen absorption while Zn and Cu nanoparticles worked more like inhibitors than activators.

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