Structural Insights and hydrogen retention in amorphous and crystalline tungsten oxide films

• Thermally grown W-oxide is crystalline orthorhombic WO₃, while electrochemically grown oxide is amorphous, with sporadic nanocrystalline domains. • T-oxide shows almost complete D release over time, while EC-oxide shows stronger D binding and prolonged retention. • Both W-oxides maintain their structural integrity upon deuterium exposure at temperatures below 370 K. • EC-oxide is suitable for long-term hydrogen storage and permeation barrier applications due to its high D retention, while T-oxide is better for rapid sensing and degassing applications. We investigated structural characteristics of and hydrogen isotope interactions with thermally and electrochemically synthesized tungsten oxide (W-oxide) thin films (≤50 nm). Specifically, we assessed whether electrochemically synthesized W-oxide could serve as a suitable proxy for thermally grown films in hydrogen interaction studies. The W-oxide thin films were exposed to low-energetic atomic deuterium (D) to explore the hydrogen uptake, retention, and intercalation effects of the W-oxide structure. The W-oxides were characterized using grazing incidence X-ray diffraction (GI-XRD), scanning and transmission electron microscopy (SEM, TEM), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR) before and after deuterium exposure. The thermally grown W-oxides are crystalline, composed of orthorhombic WO 3 , while the electrochemically grown W-oxides are amorphous with nanocrystalline domains. Deuterium retention studies revealed that the electrochemically grown W-oxides show higher initial D retention compared with their thermally grown counterparts and lower D release over time during storage, suggesting stronger D binding within the amorphous matrix. Using ion beam analysis, we quantified the deuterium retention and examined the depth-resolved reduction of the oxide within the films following deuterium exposure.