Hydrogen sorption and desorption behaviors of Mg-Ni-Cu doped carbon nanotubes at high temperature

Abstract

Hydrogen sorption and storage in a solid matrix can greatly improve its safety and efficiency when compared to the compressed gas or liquid hydrogen storage system, and kinetics mechanisms are of interest towards the development of such materials. In this study, the composites of Mg-Ni-Cu doped with singe-walled carbon nanotubes (Mg-Ni-Cu/CNTs) were synthetized. The activation performance, isothermal hydrogen sorption and desorption were systematically tested, and the experimental data were analyzed using the shrinking core model. The results show that three cycles of hydrogen sorption and desorption may be enough to fully activate Mg-Ni-Cu/CNTs and the stability can be kept for 150 cycles. A 10.1 wt% of Cu and 50.3 wt% of Ni in Mg-Ni-Cu/CNTs facilitates the hydrogen sorption and a reversible hydrogen capacity of ∼3.35 wt% can be achieved at 310 °C and 3.0 atm, and hydrogen capacity and kinetics shows significant decline during contact with 1.0 vol% CO impurity. Considering desorption at 600 °C, the kinetic profiles are about linear and desorption is completed within minutes. The gas-solid reaction processes for hydrogen sorption undergo three different rate-limiting stages, and hydrogen desorption can only be divided into two stages of surface chemical reaction and product layer diffusion.