Key Takeaways & Executive Findings
- •• The as-synthesized rN-pC exhibited H2 uptake of ~0.9 wt% at 77 K and ultralow pressure of ~0.1 bar, with an isosteric adsorption enthalpy (Qst) of ~14 kJ mol-1 H2 at zero coverage. • The 60MgH2@rN-pC started to decompose at 175 °C and released H2 of 3.38 wt% at 300 °C within 30 min, which showed outstanding desorption kinetics of MgH2 among Mg-carbon material nanocomposites. • The drawback of nanoconfinement scaffolds that cannot store hydrogen was firstly overcome. • The nanoconfined MgH2 formation enthalpy is reduced to ~68 kJ mol−1 H2 from ~75 kJ mol−1 H2 for pure MgH2, and the composite can be compressed to pellets with volumetric H2 density reaching 33.4 g L−1, surpassing 350 bar compressed H2.
Abstract
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.
1. Introduction
Clean and renewable energy is vital for sustainable development [1]. Hydrogen has high gravimetric energy density (lower heating value (LHV) ~120 MJ kg−1) [2] and zero carbon emission (only water as combustion product) [3], making it promising as energy carrier. However, the large-scale application of H2 as energy carrier is still hampered by the difficulties of effective storage [4]. Compared with storing H2 as a compressed gas at high pressures up to 70 MPa [5], or as a liquid at cryogenic temperatures (T=20 K) [6], solid-state H2 storage has the advantages of mild operation conditions (lower than 10 Mpa working pressure [7] and higher than 77 K working T [8] for storage and transportation) and reduced cost of storage systems.
Due to the high gravimetric and volumetric H2 storage density (~7.6 wt% H2 and ~110 kg m−3 H2, respectively) [9], complete heat-driven reversible transformation (MgH2 ⇌ Mg + H2) [10], and earth-abundant natural Mg containing minerals such as dolomite [11] and seawater [12], MgH2 is one of the most promising candidates for solid-state H2 storage [13]. Nonetheless, the high thermodynamic stability and kinetic reaction barriers (ΔH = ~75 kJ mol−1 H2, and ΔE = ~160 kJ mol−1 H2, respectively) [14] limit its industrial application. Zhang et al. studied the solar-driven reversible hydrogen storage of MgH2 and utilized solar energy as the sustainable energy source to reduce the energy costs [15, 16]. Besides, different approaches have been proposed to improve the thermodynamic and kinetic properties of MgH2, including alloying [17], catalysts doping [18], and nanostructuring [19].
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Yinghui Li, Li Ren, Zi Li, Yingying Yao, Xi Lin, Wenjiang Ding, Andrea C. Ferrari, Jianxin Zou (2026). Achieving Wide-Temperature-Range Physical and Chemical Hydrogen Sorption in a Structural Optimized Mg/N-Doped Porous Carbon Nanocomposite. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01931-w
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Frequently Asked Questions
What is the main achievement of this study?
The study presents the first realization of a nanoconfined Mg-based system with adsorption-active scaffolds, overcoming the drawback of nanoconfinement scaffolds that cannot store hydrogen. The composite exhibits enhanced hydrogen storage capacity and desorption kinetics.
How does the N-doped porous carbon scaffold contribute to hydrogen storage?
The N-doped porous carbon scaffold (rN-pC) not only confines Mg/MgH2 nanoparticles to prevent aggregation and improve kinetics, but also actively adsorbs hydrogen via physisorption, contributing to the total hydrogen uptake. It achieves ~0.9 wt% H2 uptake at 77 K and ultralow pressure.
What are the improved thermodynamic properties of the nanoconfined MgH2?
The nanoconfined MgH2 formation enthalpy is reduced to ~68 kJ mol−1 H2 from ~75 kJ mol−1 H2 for pure MgH2, indicating improved thermodynamics for hydrogen release and uptake.
Can the composite be used in practical applications?
Yes, the composite can be compressed into nanostructured pellets with a volumetric H2 density of 33.4 g L−1 after 500 MPa compression, surpassing the volumetric capacity of 350 bar compressed H2 (24 g L−1), making it promising for practical storage systems.
What is the significance of the wide-temperature-range hydrogen sorption?
The composite demonstrates both physisorption at low temperatures (77 K) and chemisorption at higher temperatures (e.g., 175 °C for desorption), enabling hydrogen storage across a wide temperature range, which is beneficial for various operating conditions.
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