insight - Scientific Computing - # Metal Hydrides

Proximity Effects on Interstitial Hydrogen Absorption in Strained Fe/V and Cr/V Superlattices: An Inverse Spillover Phenomenon

Q: How can the understanding of inverse hydrogen spillover be applied to improve hydrogen storage capacity in materials?

The inverse hydrogen spillover effect, as observed in the Fe/V and Cr/V superlattices, presents both challenges and opportunities for improving hydrogen storage capacity. Here's how: Challenges: Reduced Effective Storage Volume: The formation of hydrogen depletion layers near interfaces effectively reduces the volume of the material available for hydrogen storage. This is particularly significant in nanoscale systems where the surface-to-volume ratio is high. Material Selection: The choice of materials in a composite hydrogen storage system becomes crucial. Materials that exhibit strong inverse spillover effects could limit the overall hydrogen uptake. Opportunities: Interface Engineering: By understanding the factors that influence the extent of the depletion layer, such as electronic structure, strain, and defect density, researchers can potentially engineer interfaces to minimize or even reverse the inverse spillover effect. This could involve: Doping: Introducing dopants at the interface to alter the electronic structure and create a more favorable environment for hydrogen. Strain Modulation: Manipulating the strain state at the interface through careful material selection and growth techniques could influence hydrogen absorption. Surface Functionalization: Modifying the surface morphology or chemistry of the materials at the interface could alter hydrogen binding energies and diffusion pathways. Multilayer Structures: Designing multilayer structures with alternating layers of materials exhibiting different hydrogen affinities could potentially trap hydrogen within specific layers, mitigating the impact of depletion layers. Overall, a deeper understanding of inverse hydrogen spillover can guide the development of strategies to mitigate its negative effects and potentially exploit it for enhanced hydrogen storage in carefully designed materials.

Q: Could the difference in depletion layer thickness be attributed to factors beyond electronic structure, such as surface morphology or defect density at the interface?

While the study highlights the role of electronic structure in influencing the extent of hydrogen depletion layers, other factors beyond electronic effects could also contribute to the observed differences between Fe/V and Cr/V interfaces: Surface Morphology: Roughness: A rougher interface could lead to a larger effective surface area and potentially a more extended depletion layer due to increased hydrogen trapping at surface defects. Facet Formation: Different crystallographic facets can exhibit varying hydrogen binding energies, influencing hydrogen distribution near the interface. Defect Density: Vacancies and Interstitials: A higher density of vacancies or interstitials at the interface could trap hydrogen atoms, effectively increasing the depletion layer thickness. Grain Boundaries: If present, grain boundaries could act as fast diffusion pathways for hydrogen, potentially leading to a more widespread depletion zone. Intermixing: Alloying Effects: Even slight intermixing of Fe or Cr into the V layer could alter the local electronic structure and hydrogen solubility, affecting the depletion layer. Strain Distribution: Local Strain Variations: Variations in strain at the nanoscale, perhaps due to lattice mismatch or defects, could create regions with different hydrogen affinities, influencing the depletion layer profile. Experimental techniques capable of probing the interface at the atomic scale, such as high-resolution transmission electron microscopy (HRTEM) or atom probe tomography (APT), would be crucial to investigate the role of these factors in conjunction with theoretical calculations to fully understand the interplay of electronic and structural effects.

Core Concepts

The proximity of non-absorbing metals like Fe and Cr significantly influences hydrogen absorption in vanadium thin films, with Fe causing a larger hydrogen-depleted region than Cr, effectively reducing the absorbing layer thickness and impacting critical temperature and concentration.

Abstract

Bibliographic Information: Komander, K., Pálsson, G.K., Droulias, S.A., Tsakiris, T., Sörme, D., Wolff, M., & Primetzhofer, D. (Year). Inverse spillover and dimensionality effects on interstitial hydrogen. [Journal Name].
Research Objective: This study investigates the impact of proximity effects on hydrogen absorption in ultrathin vanadium films within Fe/V and Cr/V superlattices, aiming to understand the differences in hydrogen uptake and phase transitions observed in these systems.
Methodology: The researchers employed a combination of experimental techniques, including pressure-composition isotherms, resistivity measurements, and energy-resolved and channeling nuclear reaction analysis (NRA) with 15N-ions, to study hydrogen absorption, site location, and vibrational motion in the superlattices.
Key Findings: Despite identical strain states, the Cr/V superlattice exhibited higher hydrogen solubility and a higher critical temperature for phase transition compared to the Fe/V superlattice. Direct measurements revealed identical Oz-site occupancy for hydrogen in both superlattices, with similar thermal vibrational amplitudes, suggesting that the observed differences are not due to changes in site occupancy.
Main Conclusions: The study concludes that the proximity of Fe to V induces a larger hydrogen-depleted region compared to Cr, effectively reducing the thickness of the hydrogen-absorbing V layer. This reduction in effective thickness leads to finite-size effects, lowering the critical temperature and concentration in Fe/V. The observed phenomenon is termed "inverse hydrogen spillover."
Significance: This research provides crucial insights into the impact of interface effects on hydrogen absorption in metal hydrides, particularly highlighting the significance of proximity to non-absorbing metals. Understanding and controlling these effects can pave the way for tailoring the properties of metal hydrides for various applications, including hydrogen storage and catalysis.
Limitations and Future Research: While the study provides strong evidence for the inverse spillover effect, the exact mechanism behind the different depletion layer thicknesses at the Fe/V and Cr/V interfaces remains to be fully elucidated. Further theoretical and experimental investigations are needed to explore the electronic and magnetic interactions at the interfaces and their role in influencing hydrogen distribution.

Customize Summary

Rewrite with AI

Generate Citations

Translate Source

To Another Language

Generate MindMap

from source content

Visit Source

arxiv.org

Stats

Vanadium in proximity to Cr absorbs approximately 1.5 times as much hydrogen compared to Fe.
The critical temperature for Cr/V is ~196°C with a critical concentration of ~0.133 H/V.
The critical temperature for Fe/V is ~160°C with a critical concentration of ~0.078 H/V.
Hydrogen vibrational amplitudes in both superlattices are 0.20-0.25 Å.
Estimated hydrogen depletion is 2.25 Å (1.4 ML) in Fe/V and 1.6 Å (1 ML) in Cr/V.

Quotes

"Our findings are consistent with a more extended region of hydrogen depletion in the vicinity of Fe compared to Cr, which showcases an inverse of the hydrogen spillover effect."
"These findings provide strong evidence of a larger hydrogen-depleted layer at the interface to Fe than to Cr... which indirectly yields a thinner absorbing layer, which in turn is subject to finite-size induced lowering of the critical temperature."

Key Insights Distilled From

Inverse spillover and dimensionality effects on interstitial hydrogen

by Kris... at arxiv.org 11-12-2024

https://arxiv.org/pdf/2411.07067.pdf

Inverse spillover and dimensionality effects on interstitial hydrogen

Deeper Inquiries

How can the understanding of inverse hydrogen spillover be applied to improve hydrogen storage capacity in materials?

The inverse hydrogen spillover effect, as observed in the Fe/V and Cr/V superlattices, presents both challenges and opportunities for improving hydrogen storage capacity. Here's how:
Challenges:

Reduced Effective Storage Volume: The formation of hydrogen depletion layers near interfaces effectively reduces the volume of the material available for hydrogen storage. This is particularly significant in nanoscale systems where the surface-to-volume ratio is high.
Material Selection: The choice of materials in a composite hydrogen storage system becomes crucial.  Materials that exhibit strong inverse spillover effects could limit the overall hydrogen uptake.
Opportunities:

Interface Engineering: By understanding the factors that influence the extent of the depletion layer, such as electronic structure, strain, and defect density, researchers can potentially engineer interfaces to minimize or even reverse the inverse spillover effect. This could involve:

Doping: Introducing dopants at the interface to alter the electronic structure and create a more favorable environment for hydrogen.
Strain Modulation:  Manipulating the strain state at the interface through careful material selection and growth techniques could influence hydrogen absorption.
Surface Functionalization: Modifying the surface morphology or chemistry of the materials at the interface could alter hydrogen binding energies and diffusion pathways.


Multilayer Structures: Designing multilayer structures with alternating layers of materials exhibiting different hydrogen affinities could potentially trap hydrogen within specific layers, mitigating the impact of depletion layers.
Overall, a deeper understanding of inverse hydrogen spillover can guide the development of strategies to mitigate its negative effects and potentially exploit it for enhanced hydrogen storage in carefully designed materials.

Could the difference in depletion layer thickness be attributed to factors beyond electronic structure, such as surface morphology or defect density at the interface?

While the study highlights the role of electronic structure in influencing the extent of hydrogen depletion layers, other factors beyond electronic effects could also contribute to the observed differences between Fe/V and Cr/V interfaces:

Surface Morphology:

Roughness: A rougher interface could lead to a larger effective surface area and potentially a more extended depletion layer due to increased hydrogen trapping at surface defects.
Facet Formation: Different crystallographic facets can exhibit varying hydrogen binding energies, influencing hydrogen distribution near the interface.

Defect Density:

Vacancies and Interstitials:  A higher density of vacancies or interstitials at the interface could trap hydrogen atoms, effectively increasing the depletion layer thickness.
Grain Boundaries:  If present, grain boundaries could act as fast diffusion pathways for hydrogen, potentially leading to a more widespread depletion zone.

Intermixing:

Alloying Effects: Even slight intermixing of Fe or Cr into the V layer could alter the local electronic structure and hydrogen solubility, affecting the depletion layer.

Strain Distribution:

Local Strain Variations:  Variations in strain at the nanoscale, perhaps due to lattice mismatch or defects, could create regions with different hydrogen affinities, influencing the depletion layer profile.
Experimental techniques capable of probing the interface at the atomic scale, such as high-resolution transmission electron microscopy (HRTEM) or atom probe tomography (APT), would be crucial to investigate the role of these factors in conjunction with theoretical calculations to fully understand the interplay of electronic and structural effects.

If we consider hydrogen atoms as information carriers, how might this inverse spillover phenomenon inspire new ways to control information flow in nanoscale systems?

The concept of hydrogen atoms as information carriers is intriguing, particularly in the context of nanoscale systems where quantum effects become significant. Here's how the inverse spillover phenomenon could inspire new ways to control information flow:

Hydrogen-Vacancy Qubits:  The presence or absence of a hydrogen atom at a specific lattice site, particularly in conjunction with a vacancy, could represent a qubit state. The controlled migration of hydrogen, influenced by inverse spillover, could be used to manipulate these qubits.
Hydrogen-Mediated Spin Coupling: Hydrogen atoms, possessing a nuclear spin, could mediate interactions between the spins of neighboring atoms. By controlling the location of hydrogen atoms through inverse spillover, one could potentially engineer desired spin configurations or manipulate spin-based information.
Hydrogen-Based Logic Gates: The flow of hydrogen atoms, directed by carefully designed interfaces and exploiting the inverse spillover effect, could be used to construct logic gates. For example, the presence or absence of hydrogen at a junction could control the flow of electrons, mimicking a transistor-like behavior.
Hydrogen-Assisted Data Storage:  Materials exhibiting hydrogen-dependent phase transitions could be explored for data storage. The controlled insertion or removal of hydrogen, influenced by inverse spillover, could switch the material between different states representing data bits.
Challenges:

Room-Temperature Operation: Many hydrogen-related phenomena are pronounced at low temperatures. Achieving robust control at room temperature would be crucial for practical applications.
Scalability and Integration: Integrating hydrogen-based information processing elements into existing or future nanoscale architectures would be a significant challenge.
The inverse spillover effect, viewed through the lens of hydrogen as an information carrier, opens up exciting possibilities for novel information processing and storage paradigms at the nanoscale. Further research is needed to overcome the challenges and unlock the full potential of this concept.