Supraparticles for Bare‐Eye H 2 Indication and Monitoring: Design, Working Principle, and Molecular Mobility

Indicators for H 2 are crucial to ensure safety standards in a green hydrogen economy. Herein, the authors report micron‐scaled indicator supraparticles for real‐time monitoring and irreversible recording of H 2 gas via a rapid eye‐readable two‐step color change. They are produced via spray‐drying SiO 2 nanoparticles, AuPd nanoparticles, and indicator‐dye resazurin. The resulting gas‐accessible mesoporous supraparticle framework absorbs water from humid atmospheres to create a three‐phase‐system. In the presence of H 2 , the color of the supraparticle switches first irreversibly from purple to pink and further reversibly to a colorless state. In situ infrared spectroscopy measurements indicate that this color change originates from the (ir)reversible H 2 ‐induced reduction of resazurin to resorufin and hydroresorufin. Further infrared spectroscopic measurements and molecular dynamics simulations elucidate that key to achieve this functionality is an established three‐phase‐system within the supraparticles, granting molecular mobility of resazurin. Water acts as transport medium to carry resazurin molecules towards the catalytically active AuPd nanoparticles. The advantages of the supraparticles are their small dimensions, affordable and scalable production, fast response times, straightforward bare‐eye detection, and the possibility of simultaneously monitoring H 2 exposure in real‐time and ex post. Therefore, H 2 indicator supraparticles are an attractive safety additive for leakage detection and localization in a H 2 economy.