Synthesis of Polyoxometalate Complexes and their Application in Electrochemical Water-splitting

Abstract

This thesis describes the synthesis, structure characterization, and electrochemical properties of new Rubidium salt of Cobalt-based Polyoxometalate (POM) and Sodium salt of Chromium based POM. The complexes Rb2.5[(Co(H2O)6)0.5(PW12O40)].16H2O (Rb-1) and [(Cr3O(O2CC(CH3)3)6(H2O)3]3[P2W18O40]. xH2O (Na-1) were successfully synthesized in a single-pot reaction. The synthesis was done using pre-synthesized [Co2(μ OH2)(O2CCMe3)4(HO2CCMe3)4], [(Cr3O(O2CC(CH3)3)6(H2O)3](O2CCMe3)3 and tri-lacunary Keggin anion Na9[A-α-PW9O34].7H2O. The structure of Rb-1 and Na-1 was verified through FTIR and single-crystal X-ray crystallography. The crystal structure revealed a cubic crystal system with a central Co (II) surrounded by six water molecules for Rb-1 and a primitive-type monoclinic crystal structure for Na-1. Moreover, Rb-1 and Na-1 were deposited on a Ni-foam electrode and functioned as an anode for efficient OER in water splitting. The Rb-1/Ni-Foam electrode showed excellent overpotential values of 207 mV at 10 mA.cm-2 and 390 mV at 100 mA.cm-2 current densities. The electrode had fast kinetics, as indicated by a low Tafel Slope of 51.76 mVdec-1 and a small charge transfer resistance (RCT) of 5.904 ohms. The Na-1/Ni-Foam electrode showed overpotential values of 226 mV at 10 mA.cm-2 and 310 mV at 100 mA.cm-2 current densities. The electrode had fast kinetics, indicated by a low Tafel Slope of 54.6 mVdec-1 and an RCT of 12.17 ohms. Both the catalysts exhibited remarkable stability over an 8-hour test period, emphasizing their practical value and possible uses in energy applications.