Hydrogen Gasochromic Paintings Based on In Situ Synthesized Pd-H₂WO₄ Entrapped in Microgel Network

Hydrogen gasochromic sensors, which detect hydrogen gas (H₂) through naked-eye visible color changes, have special advantages such as intrinsically safe properties and less reliance on measuring instruments. To achieve room-temperature detection, hydrogen gasochromic sensors usually require catalysts such as palladium (Pd) and gasochromic materials such as oxide-containing hexavalent tungsten. However, most existent hydrogen gasochromic sensors directly expose their catalysts and sensing materials to the outer environments, which may lower their durability and environmental suitability. Herein, in this work, hydrogen gasochromic paintings with a protected microstructure are developed based on H₂WO₄ and Pd entrapped in the cores and shells of core-shell microgels. A novel fabrication strategy is developed by adopting a water-triggered reaction as the in situ synthesis method and electrosprayed core-shell droplets as the templates to generate core-shell hydrogen gasochromic microgels, which exhibit significant color changes ΔE = 24.60 under 1% H₂. The hydrogen gasochromic paintings are subsequently developed by dispersing the microgels in photo-cross-linkable hydrogel precursor solutions; the optimized paintings could exhibit excellent hydrogen-induced color changes ΔE = 15.05 and perform rapid responses within 12 min (ΔE ≥ 3) under 1% H₂. Furthermore, the hydrogen gasochromic paintings could perform irreversible responses enabling the recording of the leakage history and could maintain their sensing capabilities under humid or cryogenic environments. The high-contrast color changes and leakage-recording abilities enable low-cost automatic H₂ leakage detection using a flying drone, indicating their potential in applications requiring wide-area hydrogen leakage monitoring.