Fabricating stable CoNi active sites and elucidating the role of N in enhancing hydrogenation and dehydrogenation of MgH2

Abstract

Magnesium hydride (MgH₂) is considered a promising solid-state hydrogen storage material due to its excellent capacity and reversibility. However, its practical application is hindered by the high operating temperature. Herein, a controllable pyrolysis method was employed to synthesize N-doped carbon nanotubes anchoring highly dispersed CoNi alloy nanoparticles using a metal–organic framework (MOF) precursor, and they were introduced into a MgH₂ matrix for the first time. Surprisingly, MgH₂–CoNi@N-CNTs could achieve an initial H₂ desorption at 174 °C, which is 201 °C lower than that of pristine MgH₂ under parallel conditions. It also demonstrated excellent H₂ release and absorption kinetics and can release 6.3 wt% H₂ in 600 s at 275 °C, which is 1.7 and 4.8 times higher than those of N-deficient MgH₂–CoNi@C and pristine MgH₂, respectively. More importantly, it maintained a high desorption capacity of 5.2 wt% H₂ at 250 °C with obviously low desorption activation energy (78.6 kJ mol⁻¹). Combined with theoretical analyses, the catalytic promotion effect of N is attributed to a novel electron trafficking between the stable CoNi active sites and N-CNTs, which can significantly weaken the Mg–H bond strength and promote hydrogen absorption/desorption efficiency of MgH₂. This work provides a tunable and effective strategy for designing high-performance MgH₂ with superior catalytic efficiency.