Investigation of hydrogen diffusion in zirconia under extreme conditions†

Hydrogen embrittlement, which causes diamond anvil failure, is a significant barrier in high-pressure hydrogen experiments. Zirconia barriers show promise in reducing hydrogen permeation under pressure. We systematically calculate the diffusion behaviour of hydrogen in zirconia under high-pressure and high-temperature conditions. Our results demonstrate that phase transitions are crucial in hydrogen diffusion, with hydrogen bonds both facilitating proton transfer and acting as a drag force during reorientation. After the orthorhombic-II phase, H⁺ becomes the only stable species, and its diffusion barrier increases progressively. Environment reorientation becomes the rate-limiting step due to enhanced hydrogen bond interactions. In contrast, H⁻ shows behaviour like alumina, with a sharp decrease in diffusivity after phase transitions. The stable charge state can be easily determined by aligning the valence band maximum (VBM). Notably, only the proton-predominated hydrogen barrier can maintain high performance under pressure.