Quantitative probing of hydrogen environments in quasicrystals by high-resolution NMR spectroscopy

Abstract

Metal-based quasicrystals with unique quasi-periodic atomic arrangements are known to store a large amount of hydrogen under reasonable pressure and temperature for practical application as energy storage materials. While details on the atomic environments around hydrogen are central to understanding their hydrogen-storage capacity, the experimental probing of hydrogen environments and direct estimation of hydrogen content in hydrogen-bearing metal compounds, including quasicrystals, remain the holy grail in metallurgy and materials science because of the lack of suitable spectroscopic probes of hydrogen in noncrystalline metal alloys. While 1H nuclear magnetic resonance (NMR) measurement under fast spinning has the potential to reveal the nature of bonding around hydrogen, applying NMR to these metallic compounds has been challenging. Here, we report the first 1H nuclear magnetic resonance (NMR) spectra of hydrogenated quasicrystals under fast sample spinning, revealing previously unknown details of the bonding environment and hydrogen content. The NMR spectra of TiZrNi quasicrystals show that the metal atoms in the first coordination shell of neutral hydrogen shift gradually from Zr to Ti to Ni with increasing hydrogen content. This trend accounts for Ni-induced increase in the hydrogen-storage capacity and the enhanced desorption kinetics observed near ambient conditions. The 1H peak maximum shifted linearly toward lower frequencies with increasing hydrogen content, highlighting the utility of fast-spinning NMR as a novel quantitative probe of hydrogenated quasicrystals. These results open a new window to access the nature of hydrogen and its content in diverse hydrogen-bearing energy materials based on metal alloys using high-resolution 1H NMR spectroscopy, providing improved prospects for the hydrogen economy.