Schottky-structured CoNi-CoO@rGO for accelerating hydrogen storage in magnesium hydride

Abstract

Herein, a novel approach by designing Schottky-structured CoNi nano-alloys were introduced. After compositing with MgH2, its initial hydrogen absorption started at a low temperature of 40 °C. At a temperature of 300 °C, 6.5 wt% of H2 was released in only 10 min. Furthermore, the kinetic analysis revealed a pivotal transformation in the control model for dehydrogenation of MgH2, shifted from surface penetration to diffusion at a moderate temperature of 250 °C with the introduction of CoNi-CoO@rGO. After modification, the activation energy for hydrogen de/absorption decreased from 116 kJ/mol and 79.39 kJ/mol, to 66 kJ/mol and 54.39 kJ/mol, respectively. It is noteworthy that the CoNi-CoO@rGO-modified MgH2 exhibited excellent cycling performance, retained an impressive hydrogen storage capacity of 97% after 20 cycles at 300 °C. The innovation of this work lies in the following three aspects: 1) the uniform distribution of CoNi-CoO@rGO nanoparticles on the surface of MgH2 significantly enhanced the contact area and promoted the catalytic activity, 2) the synergistic effect between Mg2Co-Mg2CoH5 and Mg2Ni-Mg2NiH4 attenuate the intensity of the Mg-H bond and quickened the post-discharge of MgH2, 3) the incorporation of a CoO-induced Schottky structure accelerated the H transfer in MgH2 and improved the hydrogen absorption and release efficiency.