In situ visualization of misorientation-dependent hydrogen diffusion at grain boundaries of pure polycrystalline Ni using a hydrogen video imaging system

Hydrogen, the key element for solving the major environmental issues, exhibits rapid diffusion and localization in lattice defects of metals, which leads to embrittlement. However, the microstructure-hydrogen interactions in metallic materials are poorly understood. Therefore, a technique for capturing the microstructure-dependent hydrogen diffusion in real-time has long been targeted by researchers. Here, we successfully visualized the preferential hydrogen diffusion at grain boundaries (GBs) of pure Ni using a hydrogen video imaging system. A thin polyaniline layer was utilized as a hydrogenochromic sensor, and the hydrogen distribution was analyzed based on the color distribution of polyaniline. The system revealed the misorientation-dependent hydrogen flux at GBs of pure polycrystalline Ni with a micrometer-scale spatial resolution. It suggests that the geometrical structure of the GBs is a critical factor for preferential hydrogen diffusion. The use of the hydrogen video imaging system further advances the mechanistic understanding of hydrogen-material atomic interactions in polycrystalline metals and critically facilitates the development of hydrogen-related materials.