Abstract
Converting water into hydrogen through the photo-electrochemical (PEC) process is one of the most exciting approaches in this field, and there is a quest to design or search for new electro-photo-catalytic materials. In this work, simple steps for fabrication and transformation of metallic tungsten thin film into the photo-active Magnéli-phase (W18O49) of tungsten oxide thin film is demonstrated. The post-annealing temperature has a significant impact on the phase evolution of tungsten film into W18O49. The film thickness of W18O49 is controlled by controlling the sputtering time (or deposition time) of W film. The PEC performance of the as-prepared electrodes is evaluated by monitoring the water oxidation reaction under visible radiation. The PEC findings reveal a correlation between PEC performance and phase, morphology, and thickness of the film. The as-derived W18O49 can efficiently catalyze the water oxidation reaction at neutral solution pH, generating 0.6 and 1.4 mA cm−1 photo-current at 0.6 and 0.8 V vs. Saturated calomel electrode (SCE), respectively, in addition to excellent stability. The electrical conductivity and the charge transfer kinetics are investigated employing the electrochemical impedance spectroscopic (EIS) technique.
Highlights
Strong overuse and dependence of fossil fuels are intensifying air pollution and climate change
The X-ray diffraction (XRD) of films prepared after different deposition time shows sharp reflections at 26.8◦, 34.1◦, 38.1◦, 51.8◦, and 54.8◦, which are attributed to FTO glass substrate
Formation of W18 O49 was observed at a higher temperature; the of the W18O49 film evolved into a film with a thickness of 146 nm that attached as various large sheets diffraction peaks of W film annealed at 500 and 600 ◦ C matches the monoclinic phase of W18 O49, over several micrometers
Summary
Strong overuse and dependence of fossil fuels (coal, oil, and natural gas) are intensifying air pollution and climate change. Tungsten oxide is one of the most common semiconductor oxides used in PEC cells due to its ability to absorb the visible light spectrum, high stability in the electrolyte solutions, and the ability to exist in various compositional forms such as WO2 , WO3 , and W18 O49 [12,13,14]. The Magnéli-phase (W18 O49 ) [17], which is attracting considerable interest in different applications, such as solar cells, photo-catalysis, and sensors, is a non-stoichiometric tungsten oxide phase that possesses abundant oxygen vacancies [18,19]. The crystallinity, morphological features, oxidation state, oxygen vacancy, and charge transfer resistance of the fabricated films are determined and correlated to PEC performance
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