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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, the effect of proximity on interstitial hydrogen in ultrathin single‐crystalline vanadium films is demonstrated 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 a Cr/V‐superlattice. Direct measurements of hydrogen site location and thermal vibrations show identical site occupation of octahedral z at room temperature with a vibrational amplitude of 0.20–0.25 Å over a wide range of hydrogen concentrations. These 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. Interstitial hydrogen behaves distinctly at interfaces compared to the bulk. Vanadium films show proximity‐dependent hydrogen depletion near interfaces–an inverse of hydrogen spillover. Ion beam and resistivity measurements reveal Fe/V‐superlattices have lower hydrogen solubility and higher critical temperature than Cr/V due to proximity‐induced finite size effects, with similar site occupation.

Metal hydrides, based on transition metals, are a promising class of materials for hydrogen storage purposes. Understanding the effects of finite size and the presence of surfaces and interfaces in thermodynamics of hydrogen in these materials is an important step towards engineering hydride-based storage systems. In this work, hydride systems based on vanadium were studied by means of ion beam analysis (IBA), x-ray diffraction (XRD) and optical experiments. A series of thin vanadium films was grown using magnetron sputtering, with the aim of optimizing the growth conditions of the vanadium layer and improving the crystallinity of the produced films. Moreover, the correlation between the optical transmittance and the hydrogen concentration, probed through nuclear reaction analysis (NRA), of a Cr/V superlattice was studied, as a part of an on-going, large-scale investigation of proximity effects. Finally, motivated by the implications caused by the loss of hydrogen during the ex-situ hydrogenation and ion irradiation, a gas-cell aiming at performing IBA with the sample immersed in gaseous environment was designed. The effect of silicon-rich nitride membranes, holding the pressure gradient between vacuum and atmospheric pressure, on the energy and angular distribution of the primary ion beam, was studied theoretically and experimentally, proving the possibility of conducting real-space crystallographic studies using the proposed setup.

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 Å 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.