Grain-Boundary Complexion-Mediated Structural Stabilization by MOF-Derived Short-Range Motifs for Low-Temperature Hydrogen Storage in Mg(NH2)2-LiH-LiBH4 Reactive Hydride Composite

Complex hydrid e s offer high H 2 storage capacities but suffer from kinetic degradation and microstructural coarsening, requiring operations at elevated temperatures, typically above 180°C. Here, we demonstrate grain boundary complexion-mediated structural stabilization using ultra-low loading of Zr-based metal-organic frameworks (Zr-MOFs; 1 at.% Zr; UiO-66 vs. MIP-206) in the reactive hydride composite system 6Mg(NH 2 ) 2 -9LiH-2LiBH 4 (6.9.2-RHC). Incorporation of microporous Zr-UiO-66 significantly lowers the hydrogen absorption onset temperature from 162°C to 81°C, enables measurable hydrogen uptake at 35°C (1.07 wt.% under 80 bar H 2 ). In addition, UiO-66 accelerates desorption by more than threefold at 140°C, increases reversible capacity from 3.2 to 4.1 wt.%, and maintains the capacity over 15 cycles compared with the pristine 6.9.2-RHC. In situ synchrotron radiation X-ray diffraction confirms that the intrinsic amide–imide reaction pathway remains unchanged, suggesting that structural stabilization plays a dominant role in the enhanced hydrogen storage performance. SAXS reveals stabilized nanoscale domains (≈2.4–3.3 nm), while SANS/USANS demonstrates suppression of hierarchical aggregation relative to pristine 6.9.2-RHC. Ball-milling of UiO-66 preserves short-range tetrahedral structural units (≈0.76 nm) that are proposed to stabilize grain-boundary complexions capable of accommodating the large (20–30 per cent) volume changes associated with hydrogen cycling. The performance hierarchy (UiO-66 > MIP-206 > pristine) demonstrates that MOF-derived short-range structural motifs suppress coarsening by promoting grain-boundary complexions, enabling practical low-temperature hydride operation through stabilized reactive interfaces.