In the future, green hydrogen will be a key component of a climate-friendly and sustainable energy economy. Hydrogen cannot be seen, smelled or directly perceived by other human senses. However, the gas is capable of forming a highly explosive mixture even at very low concentrations. Therefore, measures must be undertaken to display hydrogen quickly, inexpensively, reliably, without electricity, safely, and most importantly, in a way that is universally understandable. This is the only way to make the future use of hydrogen in industry, but also in households, safe.   
Our approach to detect hydrogen in a simple way is a novel particle-based powder indicator concept. The special feature of this flexible, powder-based indicator derives from the structure of the individual particles. These are so-called supraparticles, which are created in the spray-drying approach and consist of thousands of smaller nanoparticles. In the case of hydrogen indicator supraparticles, various different building blocks (carrier particles, catalyst particles, dye) are used, all of which have a specific function in the detection of hydrogen gas. Due to the supraparticulate structure, it is possible to create a microenvironment in a very small space in which a sensitive dye can change its molecular structure and thus its color. When the supraparticle comes into contact with hydrogen, the gas can enter its pore system and dissociate on the reactive surfaces of the contained catalyst particles. The activated hydrogen atoms then react with the dye molecules, irreversibly reducing them in a first step, observable by a first color change from purple to pink. With continued exposure to hydrogen, the dye molecule can be further reduced and a second color change from pink to colorless can be observed. As soon as the hydrogen load is removed, the dye molecule releases the bound hydrogen and the reaction back to its pink-colored state is favoured. This creates a traffic light system that uses a simple color change to indicate the presence of hydrogen in the ambient air.
This indicator system can be easily and inexpensively manufactured on a large scale and can be used in a variety of ways. Incorporated into gloves or leak detection sprays, they can detect faulty seals in pipelines. Incorporated into a coating of, e.g., hydrogen refuelling stations, cars or heating systems, the color change can quickly and easily alert anyone to a hazard.