Wherever hydrogen is present, safety sensors are required to detect leaks and prevent the formation of flammable oxyhydrogen gas when hydrogen is mixed with air. It is therefore a challenge that today’s sensors do not work optimally in humid environments — because where there is hydrogen, there is very often humidity. Now, researchers at Chalmers University of Technology, Sweden, are presenting a new sensor that is well suited to humid environments — and actually performs better the more humid it gets.
“The performance of a hydrogen gas sensor can vary dramatically from environment to environment, and humidity is an important factor. An issue is that many sensors become slower or perform less effectively in humid environments. When we tested our new sensor concept however, we discovered that the more we increased the humidity, the stronger the response to hydrogen became. It took us a while to really understand how this could be possible,” said Chalmers doctoral student Athanasios Theodoridis, who is the lead author of the article in the journal ACS Sensors.
Hydrogen is an increasingly important energy carrier in the transport sector and is used as a raw material in the chemical industry as well as for green steel manufacturing. In addition to water being constantly present in ambient air, it is also formed when hydrogen reacts with oxygen to generate energy, for example in a fuel cell that can be used in hydrogen-powered vehicles and ships. Furthermore, fuel cells themselves require water to prevent the membranes that separate oxygen and hydrogen inside them from drying out.
Facilities where hydrogen is produced and stored are also constantly in contact with the surrounding air, where humidity varies greatly over time depending on temperature and weather conditions. Therefore, to ensure that the volatile hydrogen gas does not leak and create flammable oxyhydrogen, reliable humidity-tolerant sensors are needed there as well.
The new humidity-tolerant hydrogen sensor from Chalmers fits on a fingertip and contains tiny particles — nanoparticles — of the metal platinum. The particles act as both catalysts and sensors at the same time. This means that the platinum accelerates the chemical reaction between hydrogen and oxygen from the air leading to heat development, which causes the humidity, in the form of a film of water on the sensor surface, to boil away. The amount of hydrogen in the air determines how much of the water film boils away, and the moisture content in the air controls the thickness of the film. It is therefore possible to measure the concentration of hydrogen by measuring the thickness of the water film. And since the thickness of the water film increases as the air becomes more humid, the sensor’s efficiency increases at the same rate. The result of this process can be observed using an optical phenomenon called plasmons, where the platinum nanoparticles capture light giving them a distinct color. When the concentration of hydrogen gas in the environment changes, the nanoparticles change color, and at critical levels the sensor triggers an alarm.
At Chalmers, the development of plasmonic hydrogen gas sensors has been under way for many years. Professor Christoph Langhammer’s research team has made several major breakthroughs in the field in terms of sensor speed and sensitivity, as well as the ability to optimize sensor response and humidity resistance using AI. Previously, the group based its sensors on nanoparticles of the metal palladium, which absorbs hydrogen in much the same way as a sponge absorbs water. The new platinum-based concept, developed within the framework of the TechForH2 competence center at Chalmers, has led to the creation of a new type of sensor — a “catalytic plasmonic hydrogen gas sensor” — which opens up new possibilities.
“We tested the sensor for over 140 hours of continuous exposure to humid air. The tests showed that it is stable at various degrees of humidity and can reliably detect hydrogen gas in these conditions, which is important if it is to be used in real-world environments,” said Theodoridis.
According to the researchers’ measurements, the sensor detects hydrogen down to the parts-per-million range — 30 ppm — making it one of the world’s most sensitive hydrogen gas sensors in humid environments.
“There are growing demands for sensors that are not only smaller and more flexible, but also capable of being manufactured on a large scale and at a lower cost. Our new sensor concept satisfies these requirements well,” said Langhammer.
He also recognizes that more than one type of material may be required for future hydrogen gas sensors to function in all types of environments. “We expect to need to combine different types of active materials to create sensors that perform well regardless of the environment. We now know that certain materials provide speed and sensitivity, while others are better able to withstand humidity. We are now working to apply this knowledge going forward,” he said.
For more information, contact Christoph Langhammer at
