Synthesis of Mg2Cu nanoparticles on carbon supports with enhanced hydrogen sorption kinetics

Abstract

The reaction kinetics and reversibility for hydrogen sorption were investigated for supported Mg₂Cu nanoparticles on carbon. A new preparation method is proposed to synthesize the supported alloy nanoparticles. The motivation of using a support is to separate the nanoparticles to prevent sintering at elevated temperatures. Supported nanocrystallites with an average size of 20 nm were obtained on porous graphite and larger particles (∼300 nm) on non-porous graphite by first deposition of metallic Cu species, using solution impregnation, followed by addition of molten Mg and hydrogenation. The temperature for hydrogen release of the 20 nm particles was much lower (∼150 °C) than the micron-sized material, and the reaction was reversible with the same improved kinetic performance after several hydrogen sorption cycles. The 20 nm Mg₂Cu crystallites had a lower activation energy for the hydrogen desorption reaction compared to the bulk material (97 (±9) and 128 (±6) kJ mol⁻¹ respectively). A desorption enthalpy of 66 (±3) kJ mol⁻¹ and an entropy value of 126 (±10) J mol K⁻¹ were found for this system. The use of a porous carbon support was beneficial for obtaining Mg₂Cu nanoparticles, which improved the hydrogen sorption kinetics.