Synergistic effect of multivalent Ti, Zr, and oxygen vacancies to significantly enhance the hydrogen sorption properties of MgH2

Abstract

Magnesium hydrides have attracted great attention as one of the most promising solid-state hydrogen storage materials. However, the high dehydrogenation temperature, slow kinetics, and attenuated cycling performance limit their application. Here, amorphous ZrO₂ and few-layer Ti₃C₂ (FL-Ti₃C₂) have been homogeneously embedded into MgH₂ particles to obtain MgH₂-ZrO₂/FL-Ti₃C₂ composites by atomic layer deposition and subsequent ball milling treatment. The onset dehydrogenation temperature of MgH₂-ZrO₂/FL-Ti₃C₂ was found to be as low as 185 °C. MgH₂-ZrO₂/FL-Ti₃C₂ has been demonstrated to rapidly release 6.42 wt% H₂ within 15 min at 250 °C, whereas only 1.59 wt% H₂ was released for blank MgH₂ even at 300 °C for 1 h. MgH₂-ZrO₂/FL-Ti₃C₂ has been demonstrated to absorb 4.68 wt% H₂ within 1 min at 50 °C (30 bar H₂), and even 2.01 wt% H₂ within 15 min at 20 °C (30 bar H₂). Multivalent Ti and Zr with abundant oxygen vacancies were found to serve as electron transfer pathways that weaken the Mg–H bond and enhance the de/re-hydrogenation of MgH₂-ZrO₂/FL-Ti₃C₂. The dehydrogenation of MgH₂-ZrO₂/FL-Ti₃C₂ was observed by in situ pyrolysis HRTEM to first start from ZrO₂ and FL-Ti₃C₂. The distribution of ZrO₂ and FL-Ti₃C₂ was found to be extremely homogeneous especially after long cycles, well consistent with the excellent cycling stability (especially for kinetics) of MgH₂-ZrO₂/FL-Ti₃C₂. About 5.85 wt% of H₂ was still released after 50 cycles at 275 °C with a capacity retention of 94.2%. The successful production of MgH₂-ZrO₂/FL-Ti₃C₂ with multivalent Ti, Zr, and oxygen vacancies synergistically enhancing the hydrogen storage properties of MgH₂ provides a clear and facile path for the construction of high-performance hydrogen storage materials.