Enhancing hydrogen storage properties of MgH2 by core-shell CoNi@C

Highlights: • Core-shell CoNi@C was synthesized via hydrothermal and calcination reduction. • The onset dehydrogenation temperature of MgH₂-8 wt% CoNi@C is only 173 ^°C. • MgH₂-8 wt% CoNi@C can release 6.17 wt% of H₂ at 300 ^°C within 1800 s • MgH₂-8 wt% CoNi@C can absorb 6.0 wt% of H₂ at 150 °C within 200 s • MgH₂-8 wt% CoNi@C has excellent hydrogen absorption/desorption cycling stability. -- Abstract: Introducing multicomponent nanoparticles can improve remarkably de/hydrogenation kinetic properties of MgH₂. In this work, the original core-shell CoNi@C bimetallic nanoparticles were obtained via hydrothermal and calcination reduction technology. MgH₂-8 wt% CoNi@C starts to dehydrogenate at 173 ^°C with the dehydrogenation capacity of 5.83 wt% within 1800 s at 275 ^°C. Moreover, the composite absorbs 4.83 wt% H₂ within 1800 s at 100 ^°C with prominent advantage at low temperature. The notable improvement of hydrogen storage properties of MgH₂ is attributed to the reversible phase transitions of Mg₂Co/Mg₂CoH₅ and Mg₂Ni/Mg₂NiH₄, and the excellent thermal conductivity and confinement effect of the carbon shell. As a result, the apparent activation energy of dehydrogenation reaction reduces to 78.5 kJ/mol. This work extends the horizon of bimetallic nanoparticles with especial microstructure for enhancing the hydrogen storage properties of metal hydrides.