Achieving Wide-Temperature-Range Physical and Chemical Hydrogen Sorption in a Structural Optimized Mg/N-Doped Porous Carbon Nanocomposite

Nanoconfinement is a promising approach to simultaneously enhance the thermodynamics, kinetics, and cycling stability of hydrogen storage materials. The introduction of supporting scaffolds usually causes a reduction in the total hydrogen storage capacity due to "dead weight." Here, we synthesize an optimized N-doped porous carbon (rN-pC) without heavy metal as supporting scaffold to confine Mg/MgH₂ nanoparticles (Mg/MgH₂@rN-pC). rN-pC with 60 wt% loading capacity of Mg (denoted as 60 Mg@rN-pC) can adsorb and desorb 0.62 wt% H₂ on the rN-pC scaffold. The nanoconfined MgH₂ can be chemically dehydrided at 175 °C, providing ~ 3.59 wt% H₂ with fast kinetics (fully dehydrogenated at 300 °C within 15 min). This study presents the first realization of nanoconfined Mg-based system with adsorption-active scaffolds. Besides, the nanoconfined MgH₂ formation enthalpy is reduced to ~ 68 kJ mol^-1 H₂ from ~ 75 kJ mol^-1 H₂ for pure MgH₂. The composite can be also compressed to nanostructured pellets, with volumetric H₂ density reaching 33.4 g L^-1 after 500 MPa compression pressure, which surpasses the 24 g L^-1 volumetric capacity of 350 bar compressed H₂. Our approach can be implemented to the design of hybrid H₂ storage materials with enhanced capacity and desorption rate.