Atomic‐Scale Design, Performance Degradation Mechanisms, and System Integration of Multi‐Principal Element Hydrogen Storage Materials

Solid-state metal hydrides offer high volumetric hydrogen density and intrinsic safety for hydrogen storage, yet their practical application is severely hindered by poor room-temperature thermodynamics, sluggish kinetics, impurity gas poisoning, difficult activation, and cycling degradation. Multi-principal element alloys (MPEAs) have recently emerged as promising candidates to overcome these bottlenecks through their vast compositional space, severe lattice distortion, and synergistic cocktail effect. This review systematically summarizes recent advances in MPEAs for solid-state hydrogen storage, bridging atomic-scale design to system-level performance. A unified composition-process-structure-property framework is established that integrates engineering-driven design rules, post-processing techniques, multi-scale computations, machine learning (ML), and high-throughput experiments. Using advanced in situ and ex situ characterization, the atomic-scale origins and cross-scale evolution of surface poisoning, hydrogen-induced amorphization (HIA), disproportionation, pulverization, and defect accumulation. A theoretical framework linking electronic structure to heat and mass transport is further developed, and hydrogen storage bed design, device integration, fuel-cell coupling, manufacturing scalability, and cost analysis are discussed. Finally, key scientific and engineering challenges and future research directions are outlined. This review provides scientific guidance for designing MPEA-based solid-state hydrogen storage systems with high capacity, long cycle life, high poisoning tolerance, fast de-/hydrogenation kinetics, and low cost.