Towards Environment Friendly Hydrothermally Synthesized Li⁺, Rb⁺, In³⁺ Intercalated Phosphotungstate (PW₁₂O₄₀) Thin...

In the present investigation, a one-step hydrothermal approach is proposed to synthesize Li⁺, Rb⁺, and In³⁺intercalated PW₁₂O₄₀ (PTA) thin films. The photoelectrochemical performance of the deposited Li₃PW₁₂O₄₀ (Li-PTA), Rb₃PW₁₂O₄₀ (Rb-PTA), and In₃PW₁₂O₄₀ (In-PTA) photocathodes were investigated using a two-electrode cell configuration of FTO/Li₃PW₁₂O₄₀/(0.1 M I^-/I^3-)_aq./Graphite. The energy band gaps of 2.24, 2.11, and 2.13 eV were observed for the Li-PTA, Rb-PTA, and In-PTA films, respectively, as a function of Li⁺, Rb⁺, and In³⁺. The evolution of the spinal cubic crystal structure with increased crystallite size was observed for Rb⁺ intercalation within the PTA Keggin structure, which was confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed a modification in the surface morphology from a rod-like structure to a densely packed, uniform, and interconnected microsphere to small and large-sized microspheres for Li-PTA, Rb-PTA, and In-PTA, respectively. Compositional studies confirmed that the composing elements of Li, Rb, In, P, W, and O ions are well in accordance with their arrangement for Li⁺, Rb⁺, In³⁺, P⁵⁺, W⁶⁺, and O^2- valence states. Furthermore, the J-V performance of the deposited photocathode shows power conversion efficiencies (PCE) of 1.25%, 3.03%, and 1.62%, as a function of the incorporation of Li⁺, Rb⁺, and In³⁺ ions. This work offers a one-step hydrothermal approach that is a prominent way to develop Li⁺, Rb⁺, and In³⁺ ions intercalated PTA, i.e., Li₃PW₁₂O_40, Rb₃PW₁₂O₄₀, and In₃PW₁₂O₄₀ photocathodes for competent solar energy harvesting.