Promoting the effect of cationic substitution on thermal stability and redox properties of new synthesized Keggin type lacunary polyoxometalates (L-POMs) Ni2.5PMo11 M(H2O)O39 (M = Co, Fe, Cu, Zn)

Abstract New lacunary Keggin type polyoxometalate salts (Ni 2.5 PMo 11 M (H 2 O)O 39 / M = Co, Fe, Cu, Zn), were synthesized using the inorganic condensation method. X-ray diffraction and infrared spectroscopy results showed that the Keggin structure of the salts was preserved. The thermal stability was checked by differential scanning calorimetry coupled with thermogravimetric analysis showing that the thermal resistance was significantly improved by the incorporation of the metals into polyoxometalates. Proton and molybdenum substitution respectively by nickel and cobalt, iron, copper and zinc metals induced a positive effect on the crystallographic configuration of the prepared salts allowing them a better thermal resistance (up to 580 °C). Cyclic voltammetry revealed an interesting electrochemical property of synthesized samples, especially for Ni 2.5 PMo 11 Zn(H 2 O)O 39 sample in which the presence of zinc greatly boosted the redox behavior.