Hollow spheres known as photonic crystals, inspired by the bumpy surface of butterfly wings, magnified here 40,000 times, are the core of a new hydrogen sensor. Image Credit: RMIT University
A new prototype hydrogen sensor owes its impressive sensitivity to inspiration from the wings of the butterfly.
Hydrogen is the most simple element in the Universe, composed in its most basic form, of just one proton circled by a single electron. Hydrogen is seen as the key to clean and renewable fuel for the future, providing energy with little more than water as a by-product. Not only that, but the Universe’s lightest element is also the most abundant. This simplicity, availability, and utility come at a cost, however.
Hydrogen is highly reactive and explosive in the right conditions, as anyone who has watched footage of the Hindenberg disaster will attest. This pressing safety concern is exacerbated by the fact that hydrogen is colorless, tasteless, and scentless.
Thus, if hydrogen is to be adapted for widespread use, a sensor that can efficiently detect the element, thus alerting users to potential leaks or seepages, is highly desirable. That’s where a team of scientists from RMIT University, Melbourne, Australia, comes in.
The researchers, led by materials scientist Ylias Sabri, have developed a hydrogen sensor that works at room temperature that is both highly precise — able to detect hydrogen in low-concentrations — and light-activated. The prototype sensor takes its inspiration from an unusual source, the wings of butterflies. Their research is published in the journal ACS Sensors.
As well as being easier to use, the team’s prototype is safer than current detectors because it is powered by light rather than heat. This also stands to make the sensor much cheaper to run too.
Taking Inspiration from Butterflies
Butterflies have long been a source of fascination for scientists. Beyond simply their aesthetic appeal and the lessons they can teach us about metamorphosis in nature, the wings of these creatures have some truly fascinating properties. In particular, for materials scientists and physicists who study optics, the crystals that make up the scales on their wings.
Researchers have discovered that these crystals, as well as giving the butterfly its beautiful and varied coloration, can detect chemical agents. If you’ve ever observed a butterfly and noticed that it appears to take on a different color when viewed from a different angle, then you’ve witnessed the light refracting effect of the photonic crystals.
It’s these light-scattering properties that could help identify chemical agents and the presence of hydrogen. Of course, taking inspiration from nature is one thing, but the RMIT team sought to improve on this impressive natural feat.
The RMIT’s prototype consists of a surface coated in photonic or colloidal crystals in a way that is similar to how they exist on the wings of a butterfly. Beneath this thin surface layer of photonic crystals is a titanium palladium alloy. When the chip is exposed to hydrogen, the gas is converted to water. This generates an electric current, the magnitude of which can be measured to reveal just how much hydrogen is present.
But, just how sensitive is the sensor that the RMIT team has developed?
Improving Safety and Health with Heightened Sensitivity
Detecting hydrogen is of use in a surprisingly wide range of fields. Clearly, if hydrogen is to become a widely used fuel, the ability to detect the element before it builds to explosive quantities is, of course, of the utmost importance.
In addition to these safety issues, there is another important reason to up the sensitivity of hydrogen detectors. The presence of hydrogen in patients' breath can be a good indicator of gastrointestinal diseases (GIDs) without the need for invasive procedures, with the breath of patients often containing twice as much hydrogen as measured in healthy individuals. Even with these increased amounts of hydrogen, the amounts are still tiny — around 20 parts per million (ppm).
The hydrogen sensors currently in common use, mainly based on gas chromatography and spectrometry, require the pretreatment of exhaled organic compounds and supervision by a skilled operative.
The novel layered structure of the RMIT prototype sensor allows it to spot hydrogen in concentrations as low as 10ppm, thus making it a good candidate for a medical sensor. What is quite remarkable about this achievement is the range at which the sensor operates, making it a device that can also spot hydrogen in explosive quantities up to 40 thousand ppm. Making it a single sensor with a wide range of applications.
Sabri and the team are now seeking to patent their sensor whilst simultaneously working to further improve its already impressive sensitivity. This involves upping the device’s layers and experiment with its performance when encountering different wavelengths of light.
Some sensors can measure tiny amounts, others can detect larger concentrations; they all need a lot of heat to work. Our hydrogen sensor can do it all — it’s sensitive, selective, works at room temperature, and can detect across a full range of levels.
Ylias Sabri, Materials Scientist, RMIT
References
¹Alenezy. E. K., Sabri. Y. M., Kandjani. A. E., et al, [2020], ‘Low-Temperature Hydrogen Sensor: Enhanced Performance Enabled through Photoactive Pd-Decorated TiO2 Colloidal Crystals,’ ACS Sensors, [https://doi.org/10.1021/acssensors.0c01387]
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