Electrochemical testing of iron phosphor tungsten bronzes as potential electrode material

Abstract

In this work, synthesized 12-tungstenphosphoric acid (H3PW12O40 ∙ nH2O, PWA) was further ionically exchanged with Fe3+ ions, which led to the formation of the FePWA salt (FePW12O40 x nH2O). FePWA was then subjected to thermal analysis (TGA/DTA), which determined the phase transition temperature ( i.e., when the Keggin anion collapses). The temperature of collapsing the Keggin anion is about 600 °C, at which phosphate tungsten bronzes doped with iron (FePWB) are obtained. Obtained FePWB was further characterized by XRPD and FTIR, which confirmed the formation of the desired structure. FePWA and FePWB were examined as an electrode material for aqueous rechargeable batteries due to the channels and cavities present in their structure. Experiments were done in aqueous solutions of 6 M LiNO3 by cyclic voltammetry. The differences in the redox processes of heteropoly acid salts and iron-doped bronze were discussed thoroughly and correlated with the XRPD and FTIR results. The catalytic activity is also investigated by Briggs-Rauscher method followed potentiometricaly.