In situ formation of multiple catalysts for enhancing the hydrogen storage of MgH₂ by adding porous Ni₃ZnC_0.7/Ni loaded carbon nanotubes microspheres

Highlights

• Porous Ni₃ZnC_0.7/Ni loaded carbon nanotube microsphere is obtained.

• The microsphere in situ changes to multiple catalysts.

• The onset release temperature is reduced to 110 °C.

• It can uptake 2.34 wt% H₂ at 80 °C within 60 min.

• The E_ab and E_de are reduced to 37.28 and 84.22 KJ/mol H₂.

Abstract

MgH₂ is considered one of the most promising hydrogen storage materials because of its safety, high efficiency, high hydrogen storage quantity and low cost characteristics. But some shortcomings are still existed: high operating temperature and poor hydrogen absorption dynamics, which limit its application. Porous Ni₃ZnC_0.7/Ni loaded carbon nanotubes microspheres (NZC/Ni@CNT) is prepared by facile filtration and calcination method. Then the different amount of NZC/Ni@CNT (2.5, 5.0 and 7.5 wt%) is added to the MgH₂ by ball milling. Among the three samples with different amount of NZC/Ni@CNT (2.5, 5.0 and 7.5 wt%), the MgH₂-5 wt% NZC/Ni@CNT composite exhibits the best hydrogen storage performances. After testing, the MgH₂-5 wt% NZC/Ni@CNT begins to release hydrogen at around 110 °C and hydrogen absorption capacity reaches 2.34 wt% H₂ at 80 °C within 60 min. Moreover, the composite can release about 5.36 wt% H₂ at 300 °C. In addition, hydrogen absorption and desorption activation energies of the MgH₂-5 wt% NZC/Ni@CNT composite are reduced to 37.28 and 84.22 KJ/mol H₂, respectively. The in situ generated Mg₂NiH₄/Mg₂Ni can serve as a "hydrogen pump" that plays the main role in providing more activation sites and hydrogen diffusion channels which promotes H₂ dissociation during hydrogen absorption process. In addition, the evenly dispersed Zn and MgZn₂ in Mg and MgH₂ could provide sites for Mg/MgH₂ nucleation and hydrogen diffusion channel. This attempt clearly proved that the bimetallic carbide Ni₃ZnC_0.7 is a effective additive for the hydrogen storage performances modification of MgH₂, and the facile synthesis of the Ni₃ZnC_0.7/Ni@CNT can provide directions of better designing high performance carbide catalysts for improving MgH₂.