Colorimetric Sensor Based on Pd–MoO₃ Nanowires for Hydrogen Gas Leak Detection

The early detection of hydrogen gas leaks is crucial because of their high explosion risk. Current oxide–semiconductor-based hydrogen sensors are reliant on electrical circuits that may fail during accidents and require high temperatures, thereby raising safety concerns. Thus, there is an urgent need for the development of simpler and more intuitive sensors that can operate at room temperature. This study proposed a hydrogen sensor based on Pd–MoO₃ nanowires. The sensor exhibited a visible color change upon exposure to hydrogen at room temperature. The Pd–MoO₃ nanowires were synthesized by decorating the surface of hydrothermally produced MoO₃ nanowires with 1–5 wt.% Pd. Upon exposure to 5% hydrogen gas at room temperature, all Pd–MoO₃ nanowires exhibited distinct color changes (∆E). In particular, the MoO₃ nanowires with 3 wt.% Pd (3Pd–MoO₃) yielded an exceptionally high ∆E value of over 15 within 10 min. Further, the 3Pd–MoO₃ nanowires exhibited a noticeable color change (∆E > 1.6) within 2 min, demonstrating their potential for highly sensitive and rapid hydrogen detection. The outstanding color change of the 3Pd–MoO₃ nanowires was attributed to valence changes in both Mo (Mo⁶⁺ and Mo⁵⁺) and Pd (Pd²⁺ and Pd⁰) upon exposure to hydrogen.