Raman-Responsive Photography Strategy to Unveil Hydrogen Diffusion via a Low-Dimensional Nanocapillary

Efficient selective membranes for hydrogen separation are critical for advancing clean energy technologies, but understanding the pathways of hydrogen transport through artificial capillaries based on low-dimensional nanoarchitectures, e.g., two-dimensional materials and frameworks, remains unconquered. Here, we present a groundbreaking approach to visualize hydrogen diffusion pathways based on a Raman-responsive "photography" strategy. Leveraging the H₂-sensitive vanadium oxide as a "photographic film", the hydrogen pathway through the selective membrane is exposed on the oxide substrate. The phase transition of vanadium oxide, marked by a Raman fingerprint decay at 197 cm^-1, enables spatial-resolution tracking of hydrogen diffusion via membranes based on two-dimensional MXene, boron nitride, and zeolite. Vertical diffusion of hydrogen is restricted for nonporous membranes like boron nitride, but by introduction of pores or disruption of nanosheet assemblies, cross-plane transport can be enhanced. This technique offers a paradigm to shed light on hydrogen transport mechanisms and direct the design of next-generation selective membranes.