Achieving wide‑temperature‑range physical and chemical hydrogen sorption in a structural optimized Mg/N‑doped porous carbon nanocomposite

As the hydrogen economy accelerates, solid-state storage that delivers high gravimetric and volumetric capacity at sub-ambient and moderate temperatures remains elusive. Now, researchers from Shanghai Jiao Tong University, led by Prof. Wenjiang Ding and Prof. Jianxin Zou, report an ammonia-etched, N-doped porous carbon (rN-pC) that simultaneously acts as a nanoconfinement scaffold and an active physisorbent for Mg/MgH₂. Published in Nano-Micro Letters, the 60MgH₂@rN-pC composite releases 0.9 wt% H₂ at −196 °C and 0.1 bar, starts chemical dehydrogenation at only 175 °C, and delivers a pellet volumetric density of 33.4 g L^-1—outperforming 350 bar compressed H₂.

Why Dual-Mode Sorption Matters

• Cryogenic Gap: Conventional MgH₂ does not desorb below 280 °C, while porous carbons store only trace H₂ at ambient pressure.
• Dead-Weight Penalty: Traditional scaffolds are catalytically inert, diluting total capacity and adding mass.
• Temperature Span: Fuel-cell waste heat can be coupled to staged release if materials operate from −196 °C to <200 °C.

Innovative Design & Features

• NH₃-Activated rN-pC: Derived from ZIF-8, the scaffold offers 1 525 m² g^-1 SSA, 6 wt% pyridinic/graphitic N and a zero-coverage Qst of 14 kJ mol^-1—doubling typical carbon sorbents.
• Solution Nanoconfinement: In-situ reduction of CH₃MgCl inside carbon channels yields 20 nm MgH₂ particles that remain anchored after 30 cycles.
• Interfacial Charge Transfer: XPS and DFT reveal electron donation from MgH₂ to N sites, weakening Mg–H bonds and dropping formation enthalpy to 68 kJ mol^-1 H₂ (vs 75 kJ mol^-1 for bulk).

Applications & Future Outlook

• Record Kinetics: Full 3.4 wt% chemical desorption achieved at 300 °C in 15 min; 2 wt% released at 225 °C within 8 h—best among metal-free Mg–carbon systems.
• Hybrid Capacity: Composite stores 4.2 wt% total H₂ across two temperature windows, enabling cascade supply for PEMFC start-up and cruise.

Scalable Pellet: Cold-pressed at 500 MPa, the material retains 33.4 g L^-1 volumetric capacity, meeting DOE 2025 targets for onboard storage without heavy-metal catalysts.