Reduced graphene oxide/patronite composite as highly active catalyst precursors for enhancing the hydrogen desorption of MgH2

Abstract

Although MgH₂ is widely deemed to be the most promising solid-state hydrogen storage materials for the medium-high temperature fuel-cell applications expected in the near future, the high-temperature desorption and sluggish hydrogen absorption/desorption kinetics are the major challenges for its applications. Herein, reduced graphene oxide/patronite nanoparticle composite (rGO@VS₄) is successfully synthesized using an ionic liquid (IL)-assisted hydrothermal method, and superior catalytic effects originated from the rGO@VS₄ composite precursor towards the hydrogen storage reaction of MgH₂ are systematically investigated. The VS₄ reacts with MgH₂ leads to the in-situ formed and uniformly scattered of metallic V and MgS during both ball-milling and the initial hydrogen desorption, and the synergic catalytic effect of metallic V and MgS facilitates the improved hydrogen desorption of MgH₂. The MgH₂–15 wt% rGO@VS₄ composite starts releasing hydrogen at 180 °C and peaks at 220 °C, which is 145 °C and 128 °C lower than that of the Pristine MgH₂, respectively. The energy required for H₂ desorption from MgH₂ is decreased to 63.8 kJ mol⁻¹, 58.9 kJ mol⁻¹ lower than that of the Pristine MgH₂. Furthermore, the MgH₂–15 wt% rGO@VS₄ composite shows excellent cycling stability, of which reversible hydrogen capacity can stabilize at about 5.9 wt% with capacity retention of 98.2 % at 300 °C for 100 cycles. This study provides a deeper insight into metallic V and MgS to enhance the hydrogen desorption of solid-state hydrogen storage materials and also offers a perspective for the construction of high-activity catalysts for solid-state hydrogen storage materials.