Towards Environment Friendly Hydrothermally Synthesized Li[sup.+], Rb[sup.+], In[sup.3+] Intercalated Phosphotungstate Thin Films

In the present investigation, a one-step hydrothermal approach is proposed to synthesize Li[sup.+], Rb[sup.+], and In[sup.3+]intercalated PW[sub.12]O[sub.40] (PTA) thin films. The photoelectrochemical performance of the deposited Li[sub.3]PW[sub.12]O[sub.40] (Li−PTA), Rb[sub.3]PW[sub.12]O[sub.40] (Rb−PTA), and In[sub.3]PW[sub.12]O[sub.40] (In−PTA) photocathodes were investigated using a two-electrode cell configuration of FTO/Li[sub.3]PW[sub.12]O[sub.40]/(0.1 M I[sup.−]/I[sup.3−])[sub.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[sup.+], Rb[sup.+], and In[sup.3+]. The evolution of the spinal cubic crystal structure with increased crystallite size was observed for Rb[sup.+] 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[sup.+], Rb[sup.+], In[sup.3+], P[sup.5+], W[sup.6+], and O[sup.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[sup.+], Rb[sup.+], and In[sup.3+] ions. This work offers a one-step hydrothermal approach that is a prominent way to develop Li[sup.+], Rb[sup.+], and In[sup.3+] ions intercalated PTA, i.e., Li[sub.3]PW[sub.12]O[sub.40,] Rb[sub.3]PW[sub.12]O[sub.40], and In[sub.3]PW[sub.12]O[sub.40] photocathodes for competent solar energy harvesting.