Hydrogen is an amazing energy carrier, but the introduction of lightweight solid-state substances for compact, low-pressure storage is a great challenge. Intricate metal hydrides are a lucrative group of hydrogen storage substances, but their viability is usually limited by slow hydrogen uptake and release. Nanoconfinement, infiltrating the metal hydride within a matrix of another substance like carbon can, in certain stances; aid makes this process faster by shortening diffusion pathways for hydrogen or by altering the thermodynamic stability of the substance.
But, the Livermore-Sandia group, in conjunction with associates from Mahidol University in Thailand and the National Institute of Standards and Technology, revealed that nanoconfinement can have another potentially more vital consequence. They found that the presence of internal ‘nano – interfaces’ within nanoconfined hydrides can transform after which phases appear when the substance is cycled.
The scientists examined the big-capacity lithium nitride hydrogen storage system under nanoconfinement. Employing a link of theoretical and experimental methods, they revealed that the pathways for the uptake and release of hydrogen were basically altered by the presence of nano-interfaces, resulting to drastically faster performance and reversibility.
“The key is to get rid of the undesirable intermediate phases, which slow down the substance’s performance as they are formed or consumed. If you can do that, then the storage capacity kinetics drastically enhanced and the thermodynamic requirements to accomplish complete recharge become far more reasonable,” says Brandon Wood, an LLNL materials researcher and lead author of the paper. “In such substance, the nano-interfaces do just that, as long as the nanoconfined particles are small enough. It is really a novel paradigm for hydrogen storage, since it implies that the reactions can be altered by engineering internal microstructures.”
The Livermore scientists used a thermodynamic modelling method that goes beyond traditional descriptions to consider the contributions from the evolving solid phase boundaries as the substance is hydrogenated and dehydrogenated. They revealed that accounting for such contributions eradicates intermediates in nanoconfined lithium nitride, which was confirmed spectroscopically.
Beyond illustrating nanoconfined lithium nitride as a rechargeable, high-performing hydrogen-storage substance, the work established that adequate consideration of solid-solid nanointerfaces and particle microstructure are essential for comprehending hydrogen-induced phase transitions in intricate metal hydrides.
“There is a direct analogy between hydrogen storage reactions and solid-state reactions in battery electrode substances,” says Tae Wook Heo, another LLNL co-author on the study. “People have been considering about the role of interfaces in batteries for some time, and our work suggests that some of the similar strategies being pursued in the battery community could also be applied to hydrogen storage. Tailoring morphology and internal microstructure could be the finest way forward for engineering substances that could meet performance targets.”
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