Open Access

REVIEW

Hydrogen Storage Materials for Metal Hydride Heat Pump Systems: A Review on Selection, Classification, and Performance Improvement

Yi Zhang^1,2,*, Bing Luo³, Haibo Li⁴, Haigang Xu^1,5, Dan Zhou¹, Weijing Ding¹, Shuaijie Ding⁶, Guanmin Zhang⁶
1 Department of Energy and Power Engineering, Shandong University of Technology, Zibo, China
2 Shandong Key Laboratory of Integrated Design and Intelligence of New Energy Vehicles, Shandong University of Technology, Zibo, China
3 Shandong Huadian Energy Saving Technology Co., Ltd., Jinan, China
4 Guoneng Shouguang Power Generation Co., Ltd., Shouguang, China
5 Shandong Shifeng (Group) Co., Ltd., Liaocheng, China
6 School of Nuclear Science, Energy and Power Engineering, Shandong University, Jinan, China
* Corresponding Author: Yi Zhang. Email:

Frontiers in Heat and Mass Transfer https://doi.org/10.32604/fhmt.2026.089136

Received 15 July 2026; Accepted 16 September 2026; Published online 22 September 2026

Abstract

Metal hydride heat pumps (MHHPs) are promising for utilizing low-grade renewable thermal energy and waste heat in building heating, cooling, and temperature-upgrading applications. System performance and reliability depend heavily on hydrogen storage materials, particularly on their thermodynamics, kinetics, capacity, thermal conductivity, and resistance to cyclic pulverization. This review systematically examines these materials thermodynamically and kinetically across MHHP cycles: thermodynamics define the pressure-temperature equilibrium and reaction direction, while kinetics govern absorption/desorption rates, ultimately determining thermal power output and system responsiveness. Based on these requirements, selection guidelines are summarized, emphasizing optimal operating pressures, high enthalpy, sufficient capacity, low hysteresis, rapid kinetics, good reversibility, and long cycle life. Four major alloy families (i.e., AB₅, AB₂, AB, and A₂B) are critically analyzed alongside emerging alternatives such as A₂B₇-type La-Y-Ni alloys. To overcome performance bottlenecks, two complementary enhancement strategies are discussed: (i) thermal management via conductive additives and reactor design, and (ii) pulverization mitigation through compositional tuning, coatings, porous frameworks, and specialized forms (i.e., slurries, thin films, and amorphous alloys). Meanwhile, their economic feasibility, scalability challenges, and pilot-scale validation are discussed. Finally, future research directions are highlighted, including establishing comprehensive databases, developing high-precision kinetic models, evaluating real-world performance, and exploring novel alloys, all of which are essential for scaling MHHP technology toward sustainable energy deployment.

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Keywords

Metal hydride heat pump (MHHP); hydrogen storage materials; reaction kinetics; heat and mass transfer; thermal management

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