Scientists at TU Delft have developed innovative sensors that enable the safe and reliable use of hydrogen as a clean energy carrier, particularly in extreme environments such as aviation, polar operations, and liquid hydrogen storage. This breakthrough helps accelerate the adoption of hydrogen energy, supporting the global transition to a carbon-neutral future.
Schematic illustration of the working principle of the optical hydrogen sensor. The optical transmission of a thin film made of e.g. tantalum (Ta), is measured. When a hydrogen leak is present, part of the hydrogen is absorbed by the tantalum layer. This changes the optical properties of the thin film, and as a consequence, the optical transmission. The larger the hydrogen concentration, the more hydrogen absorbed by the tantalum layer, and the larger the optical changes are. Capping layers are used to catalyze the dissociation of the hydrogen molecule (H2) and protect the film against the environment. Image Credit: Delft University of Technology
TU Delft Scientists Team Up
To address the need for hydrogen sensors in aviation, researchers from the Faculties of Aerospace Engineering and Applied Sciences have collaborated. Supported by EU-funded projects Overleaf and HYDEA, this interdisciplinary team is working on developing the materials necessary for hydrogen detection, as well as the optical components required for integrating these sensors with other sensor technologies.
For hydrogen-powered aircraft, detecting leaks is essential for safe operation. Sensors must be placed in critical locations such as near hydrogen storage tanks, propulsion systems, and along hydrogen pipelines—areas where temperatures can drop as low as -60 °C during flight.
It remains fascinating that a layer thousand times thinner than a human hair changes its optical properties when a hydrogen leakage is present in such a way that it can even be detected by the naked eye.
Lars Bannenberg, Delft University of Technology
The Key is in the Material
The effectiveness of the sensor lies in the materials used to build it. These materials, metal-hydrides less than 100 nanometers thick, can reversibly absorb hydrogen from their environment. This absorption alters their optical properties, allowing the hydrogen concentration near the sensor to be measured based on changes in optical transmission.
While this principle seems straightforward, developing such a material is a complex challenge. There are many requirements for these materials, and their behavior at such thin layers is vastly different from traditional materials. One crucial requirement is response time—sensors must react within 10 seconds, with an ideal response time of just one second.
Fun Fact: Freezer Fine Tuned
Processes like molecular hydrogen dissociation and diffusion slow down considerably at low temperatures, making it difficult to detect hydrogen and prolonging the sensor's response time. It is challenging to set up a system that allows testing of the materials for a sensor because the researchers had to introduce a well-defined leak with a certain hydrogen concentration in a -60 °C environment.
For this, the team created an experimental setup from the ground up for this. This proved to be very difficult, particularly because the global pandemic disrupted supply chains.
For instance, they had to come up with inventive solutions because all of the lab freezers that were used to store vaccines were sold out. The researchers used parts from a variety of vendors, such as do-it-yourself shops and a freezer that was first made to hold tuna. This freezer was completely converted and served as the backbone of this study.
First Results and Follow Up
The key novelty of the work is its demonstration that these sensors remain effective at temperatures as low as -60 °C. This breakthrough addresses a significant challenge in Ziqing Yuan’s Ph.D. research: identifying suitable materials for extreme conditions.
TU Delft’s patented tantalum-based hydrogen sensing materials exhibit substantial changes in optical properties, making them viable for sensing applications even at low temperatures. Additionally, Yuan achieved response times under 10 seconds.
Interestingly, her in-depth analysis revealed that the response was not limited by hydrogen atom diffusion within the material but rather by the dissociation of hydrogen molecules at the sensor’s surface. This insight not only deepens the fundamental understanding of these materials but also provides clear directions for further improving their performance.
Lars Bannenberg added: “The journey to the perfect hydrogen sensor does not end here. TU Delft scientists are working on developing advanced optical methods to implement the sensors. This would enable obtaining information on the hydrogen concentration at multiple positions inside the aircraft with just one system.”
On top of that, we will be testing the sensor under more realistic conditions. Including environments where also gaseous pollutants such as CO are present, in high-humidity conditions that can be encountered in the tropics, and in a range of other conditions provided by the test set-ups of the partners in our European projects.
Lars Bannenberg, Delft University of Technology
Journal Reference:
Yuan, Z., et al. (2025) Optical Hydrogen Sensing Materials for Applications at Sub-Zero Temperatures. Advanced Functional Material. doi.org/10.1002/adfm.202420087