Nature inspires a new hydrogen sensor

Some see hydrogen as the fuel of the future, with the potential to service energy-intensive industries – like aviation, shipping and manufacturing – that would tax wind and solar power.

But since hydrogen is a colourless, odourless, tasteless and highly flammable gas, it poses a high risk, so unsurprisingly, research into hydrogen technology has included a focus on developing excellent sensors.

Now, materials scientist Ylias Sabri and colleagues at Australia’s RMIT University have developed a prototype of an ultra-precise, light-activated sensor that works at room temperatures.

The secret? Butterflies.

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A butterfly’s wings are beautiful and, in this case, inspirational Credit: Alejandro Santillana, University of Texas

The surface of this new sensor is covered in bumpy, carefully spaced microstructures that imitate a butterfly’s wing. In butterflies, such nanostructures affect how light reflects off to create iridescent colours, while the sensor uses these microscopic bumps – called photonic or colloidal crystals – to trap light efficiently. This allows it to draw all the energy it needs from a beam of light, rather than requiring heat.

The prototype, described in the journal ACS Sensors, comprises an electronic chip coated first in a thin layer of these photonic crystals, then a titanium palladium alloy. When the chip is exposed to hydrogen, the gas is converted into water and triggers an electric current, the magnitude of which indicates the precise level of hydrogen present.

Sabri, this prototype streaks ahead of any hydrogen sensor currently on the market. “Some sensors can measure tiny amounts, others can detect larger concentrations; they all need a lot of heat to work,” he explains. “Our hydrogen sensor can do it all – it’s sensitive, selective, works at room temperature and can detect across a full range of levels.”

The sensor can pick up hydrogen at concentrations of as little as 10 parts per million (useful for medical diagnoses) and as high as 40,000 parts per million (useful to detect explosive amounts).

Since the sensor runs on light instead of heat, it’s cheaper and safer to run than other commercially available sensors, which typically operate between 150 and 400 degrees Celsius. It is also highly selective, able to accurately distinguish hydrogen from other gases, which current sensors struggle with.

Co-researcher Ahmad Kandjani says this broad detection range and selectivity would be extremely useful if hydrogen is integrated into the energy system.

“By delivering precise and reliable sensing technology that can detect the tiniest of leaks, well before they become dangerous, we hope to contribute to advancing a hydrogen economy that can transform energy supplies around the world,” he says.

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The sensor is made with an electronic chip covered with
photonic crystals and a titanium palladium composite.
Credit: RMIT University

The team is currently pursuing a patent and expects the sensor to be applied in a range of areas – including improving human health.

Many gastrointestinal disorders have been linked to elevated levels of hydrogen in the gut. Patients are typically diagnosed using a breath sample processed by a lab, but Sabri believes their sensor could be built into a hand-held device and thus deliver immediate results.

“With gut conditions, the difference between healthy levels of hydrogen and unhealthy levels is miniscule – just 10 parts per million – but our sensor can accurately measure such tiny differences,” he says.

Their study predicts that the sensitivity can be improved even further, down to 2.5 parts per million. This will also be useful in hydrogen fuel cells or battery technology.

Current sensors, Sabri says, aim to detect hydrogen leaks once they reach 1-2% in the air, which is quite close to 4% – the threshold at which hydrogen becomes explosive.

“What we try to do is to look at it from the parts per million level, so we know as soon as there’s any leak,” Sabri says. “It just gives more confidence to future users of hydrogen technologies… The more sensitive and selective your sensor is, the more confidence you can provide to your end users.”

To heighten their device’s sensitivity, the team will be experimenting with making the device multi-layered, trying with different wavelengths of light, and varying the materials, including using different semiconductors.

“We’re going to see how good we can actually make this thing,” Sabri concludes.

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