Effect of high-activity Co/CeO₂@C on hydrogen storage kinetics of MgH2

Magnesium hydride (MgH₂) is a promising solid-state hydrogen storage material for large-scale applications, owing to its high gravimetric capacity and natural abundance. However, its practical implementation is hindered by high thermodynamic stability and sluggish kinetics, originating from strong Mg–H bonds and limited hydrogen diffusion, which typically require elevated temperatures and prolonged cycling. Moreover, existing catalytic systems frequently suffer from inadequate dispersion, interfacial instability during cycling, and a lack of quantitative understanding of the cooperative effects between oxygen vacancies and multivalent Ce. To address these issues, a Co/CeO₂@C composite catalyst was synthesized through a hydrothermal–calcination method and incorporated into MgH₂ via ball milling. The microstructural characteristics, hydrogen storage properties, and underlying reaction mechanisms were systematically investigated using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Pressure-Composition-Temperature (PCT) tests and Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetic fitting. Evaluation based on microstructure, hydrogen uptake/release capacities at varying doping levels, and corresponding activation energies revealed that the composite with 6   wt.% Co/CeO₂@C exhibited a hydrogen uptake of 5.74   wt.%. At 300 °C, the 6   wt.% composite released 5.15   wt.% H₂ within 100   min, demonstrating its superior dehydrogenation performance at this doping level. The activation energy decreased from 145.43   kJ·mol⁻¹ to 93.35   kJ·mol⁻¹, and the thickness loss due to interfacial degradation was less than 1   nm. This enhancement is ascribed to a triple synergistic mechanism of “hydrogen spillover–electron transfer–confinement stabilization”. Co offers active sites for hydrogen dissociation, oxygen vacancies in CeO₂ promote hydrogen diffusion, and the carbon matrix suppresses particle agglomeration. This study contributes to quantitatively understanding the synergy between oxygen vacancies and multivalent Ce, establishes a clear “microstructure–catalytic mechanism–macro-performance” correlation, and offers new insights for the practical deployment of Mg-based hydrogen storage materials. It is noted, however, that the key findings presented herein align closely with trends reported in prior literature, highlighting the consistent performance landscape observed for this class of catalytic modifiers.