Inverse spillover and dimensionality effects on interstitial hydrogen

TL;DR

This study investigates how interfaces in ultrathin vanadium films affect hydrogen absorption, revealing inverse spillover effects and providing insights for hydrogen storage and catalysis.

Contribution

It demonstrates the impact of interface proximity on interstitial hydrogen behavior in ultrathin vanadium films, highlighting inverse spillover effects in Fe/V and Cr/V superlattices.

Findings

Cr/V-superlattice shows higher hydrogen solubility and critical temperature.

Hydrogen occupies octahedral sites with similar vibrational amplitudes across samples.

Inverse spillover effect observed near Fe compared to Cr.

Abstract

Nanoscaling interstitial metal hydrides offers opportunities for hydrogenation applications by enhancing kinetics, increasing surface area, and allowing for tunable properties. The introduction of interfaces impacts hydrogen absorption properties and distribution heterogeneously, making it however challenging to examine the multiple concurrent mechanisms, especially at the atomic level. Here we demonstrate the effect of proximity on interstitial hydrogen in ultrathin single crystalline vanadium films, by comparing hydride formation in identically strained Fe/V- and Cr/V-superlattices. Pressure concentration and excess resistivity isotherms show higher absolute solubility of hydrogen, higher critical temperature and concentration in the Cr/V-superlattice. Direct measurements of hydrogen site location and thermal vibrations show identical occupation of octahedral z sites at room temperature with a vibrational amplitude of 0.20-0.25 {\AA} over a wide range of hydrogen concentrations. 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. Advancing the understanding of interface effects resolves previously puzzling differences in the hydrogen loading of Fe/V- and Cr/V-superlattices and is relevant for advancing both catalysis and storage.