Palladium nanoparticle deposition onto the WO 3 surface through hydrogen reduction of PdCl 2: Characterization and gasochromic properties

Abstract

Nowadays, gasochromic Pd/WO 3 coatings as optically switchable materials have become more applicable for hydrogen sensors and smart windows. In this study, WO 3 films were prepared by Pulsed Laser Deposition (PLD) and spin-coating sol–gel techniques. For deposition of Pd, first a layer of PdCl 2 was obtained via a simple drop-drying process by dropping PdCl 2 solution onto WO 3 substrates and drying them at room temperature. Then Pd nanoparticles were synthesized via hydrogen gas exposure that causes reduction of the PdCl 2 layer. According to Scanning Electron Microscope (SEM) observations before hydrogen reduction, many individual nanoparticles or fractal-like constructions of palladium were formed in the PdCl 2 layer in which the fractal branches were distorted after hydrogen treatment. Surface chemistry of the observed Pd nanoparticles was studied using X-ray Photoelectron Spectroscopy (XPS) at different stages of the reduction process. The results showed that after hydrogen treatment, the chlorine atoms were desorbed from the PdCl 2 layer and a metallic Pd layer remained on the surface of WO 3. Gasochromic properties in the presence of H 2 or O 2 gases for different PdCl 2 amounts revealed that the rate and saturated level of coloring depends on the PdCl 2 amounts as well as on the preparation method of the WO 3 substrates due to different porosities.