This study reports the fast hydrogenation and dehydrogenation of ultra-thin discrete platinum/palladium (Pt/Pd) bimetal over nano-structured Ag islands grown on rough alumina substrate by a RF magnetron sputtering technique. The morphology of Ag nanoislands was optimized by RF magnetron sputtering and rapid thermal annealing process. Later, Pt/Pd bimetal (10/10) nm were deposited by RF magnetron sputtering on the nanostructured Ag islands. After the surface morphological optimization of Ag nanoislands, the resultant structure Pt/Pd@Ag nanoislands at alumina substrate showed a fast and enhanced hydrogenation and dehydrogenation (20/25 s), response magnitude of 2.3% (10,000 ppm), and a broad detection range of 500 to 40,000 ppm at the operating temperature of 120 °C. The superior hydrogenation and dehydrogenation features can be attributed to the hydrogen induced changes in the work function of Pt/Pd bimetal which enhances the coulomb scattering of percolated Pt/Pd@Ag nanoislands. More importantly, the atomic arrangements and synergetic effects of complex metal alloy interfacial structure on Ag nanoislands, supported by rough alumina substrate incorporate the vital role in accelerating the H2 absorption and desorption properties.