Using conventional X-rays and lasers to detect the atomic state of hydrogen is quite challenging, given its small size. A Tohoku University group of researchers may have overcome this barrier by unveiling a new visualization technique that employs an optical microscope and polyaniline to paint a better picture of how hydrogen behaves in metals.

The group has created a simple and inexpensive means to visualize the atomic state of hydrogen.

Details of their breakthrough have been published in the journal Acta Materialia.

(a) Comparison of the spatial and time resolutions between the conventional hydrogen detection techniques and the hydrogen visualization technique developed in this study. (b) A schematic of the present hydrogen visualization technique. Image Credit: Tohoku University. ©Hiroshi Kakinuma et al. Click here for the press release and a larger view of the image and click here for the open access study paper.

Hydrogen or dihydrogen, is carbon dioxide free, and it has long been touted by some as a fuel source for clean energy. Yet, shifting society towards a hydrogen energy-based one requires overcoming some significant technical issues.

An essential is structural and functional materials that produce, store, transport and preserve hydrogen. To develop advanced materials for hydrogen-related applications, a fundamental understanding of how hydrogen behaves in alloys is crucial.

However, current technology falls short in this area. Detecting atomic state hydrogen – the smallest atom in the universe – with X-rays or lasers is challenging due to its unique characteristics.

Researchers are currently focusing on better analytical and visualization techniques that can incorporate high spatial and time resolutions simultaneously.

Hiroshi Kakinuma, an assistant professor at Tohoku University, and his co-authors developed a new visualization technique harnessing an optical microscope and polyaniline layer.

Kakinuma noted, “When the color of the polyaniline layer reacts with the atomic state hydrogen in metals, it changes colors, allowing us to analyze the flow of hydrogen atoms based on the color distribution of the polyaniline layer. Additionally, optical microscopes can observe the sub-millimeter-scale view with microscale spatial resolution in real time, thereby capturing hydrogen behavior with unprecedented high spatial and time resolutions.”

Thanks to this method, the researchers successfully filmed the flow of hydrogen atoms in pure nickel (Ni). The color of polyaniline changed from purple to white when reacting with hydrogen atoms in a metal.

The in situ visualization revealed that hydrogen atoms in pure Ni preferentially diffused through grain boundaries in disordered Ni atoms. Furthermore, the group found that hydrogen diffusion was dependent on the geometrical structure of the grain boundaries: the hydrogen flux grew at grain boundaries with large geometric spaces.

These results experimentally clarified the relationship between the atomic-scale structure of pure Ni and the hydrogen diffusion behavior.

The approach has broader applications as well. It can be applied to other metals and alloys, such as steels and aluminum alloys, and drastically facilitates elucidating the microscopic hydrogen-material interactions, which could be further investigated through simulations.

“Understanding hydrogen behaviors related to the atomic-scale structure of alloys will enable efficient alloy design, which will dramatically accelerate the development of highly functional materials and usher us one step closer to a hydrogen energy-based society,” added Kakinuma.


This is quite the best of news for the hydrogen enthusiasts. So far little progress has been made in keeping the smallest atom under control. Only gravity has a noteworthy effect in gas giants and stars. On earth free hydrogen has a tendency to escape into space.

But now a much better view is possible. Perhaps it is enough to make a few big strides in hydrogen storage and handling. Today industrial hydrogen is almost immediately put to use.

Being able to store it under significant pressure for weeks would be a breakthrough. That might be a very significant breakthrough. So far nature on earth has used combining hydrogen with water and carbon for storage and handling. That has given life as we know a foundation. What mankind’s technology can accomplish is yet to be seen.


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