Modification of MgH₂ hydrogen storage performance by nickel-based composite catalyst Ni/NiO

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Magnesium hydride (MgH₂) is a promising material for hydrogen storage due to its high hydrogen capacity.
• However, MgH₂ suffers from poor kinetics and high dehydrogenation temperatures, limiting its practical application.
• Catalysts are crucial for improving the hydrogen storage performance of MgH₂.

Purpose of the Study:

• To investigate the effect of Ni/NiO catalyst on the hydrogen storage properties of MgH₂.
• To evaluate the dehydrogenation and rehydrogenation kinetics and thermodynamics of MgH₂ enhanced with Ni/NiO.
• To understand the role of the catalyst in the hydrogen storage cycle.

Main Methods:

• Synthesis of MgH₂ with 10 wt% Ni/NiO catalyst.
• Thermogravimetric analysis (TGA) to study dehydrogenation and rehydrogenation behavior.
• Differential scanning calorimetry (DSC) to determine activation energies.
• Cyclic testing to assess long-term stability.

Main Results:

• The MgH₂+10 wt% Ni/NiO composite exhibited enhanced dehydrogenation starting at ~180 °C, releasing 5.83 wt% hydrogen by 300 °C in 10 min.
• Rehydrogenation commenced around 50 °C, with the material absorbing ~4.56 wt% hydrogen in 10 min at 150 °C.
• The activation energies for dehydrogenation and rehydrogenation were determined to be 87.21 kJ/mol and 34.84 kJ/mol, respectively.
• The formation of Mg₂Ni/Mg₂NiH₄ during cycling promoted hydrogen diffusion.

Conclusions:

• Ni/NiO catalyst significantly enhances the hydrogen storage performance of MgH₂.
• The catalyst lowers dehydrogenation temperatures and improves hydrogen absorption/desorption kinetics.
• The Mg₂Ni/Mg₂NiH₄ intermediate phase plays a vital role in facilitating hydrogen diffusion during cycling, indicating potential for practical hydrogen storage applications.