Effect of CNT-referenced FeVO4 as a catalyst on the hydrogen absorption and desorption characteristics of MgH2

Magnesium hydroxide has garnered significant interest in recent years due to its outstanding hydrogen storage capabilities, favorable reversibility, and cost-effectiveness. Nonetheless, high thermodynamic stability and slow reaction kinetics have restricted its practical utilization. To enhance the hydrogen storage efficiency of MgH₂, a new bimetallic oxides oxide-doped CNT catalyst, FeVO₄/CNT, was synthesized through hydrothermal and calcination processes to improve its catalytic activity. Doping MgH₂ with 6 wt.% FeVO₄/CNT significantly reduced its dehydrogenation temperature to 198 °C, compared with 287.6 °C for untreated MgH₂. The FeVO₄/CNT-catalyzed MgH₂ sample achieved a hydrogen desorption of 4.11 wt.% within 30 min at 285 °C, while hydrogen absorption reached 6.02 wt.% at a reduced temperature of 150 °C. Calculations using the Kissinger method indicated that the activation energy for the FeVO₄/CNT-catalyzed dehydrogenation reaction of MgH₂ was reduced to just 95.2 kJ/mol, compared with 141.8 kJ/mol for untreated MgH₂. Through fitting of the kinetic model calculation, this study showed that the hydrogen storage system can improve its hydrogen absorption efficiency by adding an FeVO₄/CNT catalyst to control the rate and change from a permeation model to a diffusion model. The study further reveals that the MgH₂-6FeVO₄/CNT composite forms in-situ V and Fe nanoparticles during ball milling, which remain structurally stable throughout subsequent hydrogenation/dehydrogenation cycles. The in-situ generated V and Fe nanoparticles contributed to sustained hydrogen release properties over 10 cycles, demonstrating 94% retention of initial dehydrogenation capacity.