Regulation Mechanism of Bi2O3 Doping on Microstructure and Hydrogen Storage Properties of CeMg11Ni Alloy

To improve the sluggish low-temperature hydrogen storage kinetics of RE-Mg-based alloys, Bi2O3 is introduced into CeMg11Ni as a functional dopant for microstructural regulation, and CeMg11Ni + x wt.% Bi2O3 (x = 0, 3, 5, 7, 10) composites are fabricated through planetary ball milling. Multiple characterization methods including XRD, SEM and TEM were used to explore the effects of Bi2O3 on the microstructure and hydrogen storage properties. Bi2O3 maintains stable phase during cycling and does not participate in reversible hydrogen storage reactions. It cooperates with in situ formed CeH2 nanocrystals to construct high-density interfacial defects. The 5 wt.% Bi2O3-doped alloy exhibits the optimal balance between exposed catalytic sites and open hydrogen diffusion channels, achieving complete dehydrogenation within 144 s at 633 K, a reduced dehydrogenation activation energy of 63.89 kJ mol−1, and an 84.7% hydrogen absorption ratio within 5 min at 423 K. Bi2O3 has a weak effect on the thermodynamic properties of the alloy, with only a slight enthalpy change of less than 1 kJ/mol within the experimental error range. Bi2O3 enhances hydrogen storage reactions through a synergistic “active sites–diffusion channels” mechanism, in which oxygen vacancies promote H2 dissociation and heterogeneous interfaces facilitate hydrogen diffusion, thereby reducing the reaction energy barrier.