New gasochromic system: nanoparticles in liquid

In this study, WO₃ nanocrystallites were first produced by laser ablation of W target in deionised water. To synthesize palladium, a PdCl₂ solution (0.2 g/L) was added to the liquid. Transmission electron microscope revealed successful synthesis of tungsten oxide nanocrystallites along with the production of Pd and core–shell Pd/WO₃ nanoparticles. Gasochromic behavior was examined by hydrogen bubbling into Pd/WO₃ liquid in which a transition to blue absorbing state was observed. Optical absorption spectra of the colored liquid represented different sharp small polaron absorbing peaks below 3 eV and the peaks intensity was observed to be varied with Pd:WO₃ ratio. Time variations of optical density difference (∆OD) were measured at constant wavelength of 632.8 nm by alternative bubbling hydrogen or oxygen gases. The ∆OD in the first coloring cycles were not completely reversible owing to the presence of some unreacted PdCl₂. The further coloring bleaching indicates a normal gasochromic behavior.