Polymer-Nanoparticle Hybrid Materials for Plasmonic Hydrogen Detection

Doctoral thesis, 2021

How Colorful Metal Nanoparticles May Ensure the Safety of Hydrogen-Fueled Vehicles!

Metallic nanoparticles have been used since medieval times to stain glass. One can see such beautiful pieces of art in old church windows, for example. Their bright vibrant colors stem from the unique ability of metal nanoparticles to absorb and scatter light. For centuries, their use has therefore been limited to art, until it only quite recently was discovered that their color can vary due to a change in their closest surroundings. In fact, this means that one can use metal nanoparticles as tiny sensors for small molecules, which are impossible to see by the naked eye! Therefore, today metal nanoparticles and the phenomenon called a “plasmon” are used in many sensor applications, and I have used them to detect hydrogen gas.

Why hydrogen gas?

You may have heard about hydrogen-fueled cars in the news. Hydrogen is an alternative energy carrier, which promises a clean and green-house gas emission free energy system. One can in principle “mine” hydrogen from water and then use it to power vehicles, with the only product again being pure water. Therefore, in the near future, hydrogen will provide energy for cars, buses, ships and even airplanes.

Unfortunately, however, hydrogen is also flammable when mixed with air, even at relatively low concentrations, and it takes a less intense spark to ignite hydrogen than gasoline. Furthermore, hydrogen is odorless and invisible - thus, we need sensors to detect leaks to enable its safe use.

Which metallic nanoparticles can be used to detect hydrogen?

Commonly famous as jewelry metal, Palladium is known to absorb hydrogen gas in large amounts, very much in analogy to how a sponge absorbs water. Furthermore, Palladium nanoparticles change their color when they absorb hydrogen and the amount color change corresponds to the amount of hydrogen in their surroundings. Therefore, they can be used as a means to measure hydrogen concentration!

Nanoparticles encapsulated in plastic!

In real applications, hydrogen sensors will be used in harsh environments. Therefore, a plastic coating around the tiny palladium nanoparticles can protect them from species that would “block” their surfaces and deactivate them, like oxygen or carbon monoxide. However, as it turns out, like killing three birds with one stone, the plastic is not only for protection but it also accelerates the sensor’s response time by accelerating the hydrogen uptake rate and it enhances the color-change contrast, thereby making the sensor more sensitive.

In this thesis …

…I comprehensively study and design plastic-encapsulated Pd nanoparticles – so-called hybrid materials – to achieve high performance hydrogen sensors, with the aim to push their performance closer industrial requirements. In a wider perspective, my thesis thus contributes to the dissemination of hydrogen energy technologies for a cleaner and more sustainable energy system. Beyond that, hydrogen sensors also find wide application in nuclear power safety, in the chemical and electricity network industries or for medical diagnostics.