Highly dispersed metal nanoparticles on TiO_2 acted as nano redox reactor and its synergistic catalysis on the hydrogen storage properties of magnesium hydride

摘要

In this paper, we have synthesized highly dispersed Co metal nanoparticles with the particle size about 5-10 nm on TiO2 (25-50 nm) for the first time through an extremely facile solvothermal method. It is supposed that the synthesized Co/TiO2 composite can combine the catalytic advantage of both Co and TiO2, exhibiting the superior catalytic effect on the hydrogen de/absorption properties of MgH2. The experimental data confirmed the above supposition and demonstrated that Co/TiO2 additive highly enhances the hydrogen de/absorption kinetics of MgH2 as compared to separate Co or TiO2 additive. Specifically, the MgH2-Co/TiO2 composite begins to desorb hydrogen at about 190 degrees C with a low apparent activation energy of 77 kJ/mol. Besides, the MgH2-Co/TiO2 composite has a desorption peak temperature of 235.2 degrees C, which is 53.2, 94.2 and 132.2 degrees C lower than that of MgH2-TiO2 (288.4 degrees C), MgH2-Co (329.4 degrees C) and ball-milled MgH2 (367.4 degrees C). Moreover, MgH2-Co/TiO2 composite also exhibits low temperature rehydrogenation properties, which can absorb 6.07, 5.56 and 4.24 wt% H-2 within 10 min at the temperature of 165, 130 and 100 degrees C, respectively. It is supposed that such excellent hydrogen desorption properties and low desorption energy barrier of MgH2-Co/TiO2 composite are mainly ascribed to the novel synergistic catalytic effects of Co and TiO2. Herein, we propose a novel catalytic mechanism and think that Co/TiO2 acts as "nano redox reactor", which can facilitate the dissociation and recombination process of hydrogen, thus reducing the reaction energy barrier and enhancing the de/rehydrogenation of MgH2. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.