Improving MgH₂ hydrogen storage with oxygen vacancy-enriched H-V₂O₅ nanosheets as an active H-pump

With the depletion of fossil fuels and global warming, there is an urgent need to seek green, clean, and efficient energy resources. Against this backdrop, hydrogen is considered a potential candidate for replacing fossil fuels due to its high energy density and environmentally friendly nature. To realize the development of a hydrogen economy, safe and efficient hydrogen storage technologies are crucial.

Compared to traditional compressed hydrogen and cryogenic liquid hydrogen storage technologies, solid-state hydrogen storage is considered a safer and more efficient method. Magnesium hydride (MgH₂), as one of the most promising solid-state hydrogen storage materials, has attracted attention due to its abundant elemental resources, high hydrogen storage capacity, good reversibility, and non-toxicity. However, the relatively high operating temperature of MgH₂ limits its large-scale commercial application in vehicular or stationary hydrogen storage.

Introducing transition metal-based catalysts with unique three-dimensional electronic structures is considered an effective method to improve the kinetics of MgH₂. Vanadium (V) and its oxides are often used as catalysts for MgH₂ due to their multivalence and high catalytic activity. However, due to the high ductility of metallic vanadium and relatively low activity, vanadium-based oxides have broader application prospects.

Layered V₂O₅ with a layered structure is one of the promising catalysts to enhance the hydrogen storage performance of MgH₂/Mg, but limited catalytic capacity due to insufficient contact between V₂O₅ and MgH₂.

To address this issue, Dr. Jianxin Zou's team at Shanghai Jiao Tong University employed a solvothermal method followed by subsequent hydrogenation to prepare ultra-thin hydrogenated V₂O₅ nanosheets with abundant oxygen vacancies and used them as catalysts to improve the hydrogen storage performance of MgH₂.

The study is published in the journal Nano-Micro Letters.

The MgH₂-H-V₂O₅ composite material exhibits excellent hydrogen storage performance, including a lower desorption temperature (T_onset = 185°C), rapid desorption kinetics (E_a = 84.55 kJ mol⁻¹ H₂ for desorption), and long-term cyclic stability (capacity retention of up to 99% after 100 cycles). Particularly, the MgH₂-H-V₂O₅ composite material shows outstanding hydrogen absorption performance at room temperature, with a hydrogen absorption capacity of 2.38 wt% within 60 minutes at 30°C.

The H-V₂O₅ nanosheets synthesized by Dr. Zou's team possess a unique two-dimensional structure and abundant oxygen vacancies, enabling the in-situ formation of V/VH₂ during the reaction process, all of which contribute to enhancing the hydrogen storage performance of MgH₂.

By using a solvothermal method to create a distinct anisotropic layered structure, a highly exposed surface is formed, thereby providing more active sites and pathways for hydrogen/electron diffusion, thus improving hydrogen storage performance. Moreover, crucially, the presence of oxygen vacancies accelerates electron transfer, stimulating the "hydrogen pump" effect of VH₂/V, facilitating the dehydrogenation of VH₂ and MgH₂, and reducing the energy barriers for hydrogen dissociation and recombination.

Introducing oxygen vacancy defect engineering into the catalyst thus opens up a new avenue for enhancing the cyclic stability and kinetic performance of MgH₂.