Layered Vanadium Phosphates as Electrodes for Electrochemical Capacitors Part II: The Case of VOPO 4 •CTAB and K 0.5 VOPO 4 •1.5H 2 O

Abstract

VOPO 4 •2H 2 O was synthesized and investigated as an electrode material for electrochemical capacitors, so-called supercapacitors. The electrochemical characterizations were performed in three different electrolytes (3M LiNO 3 , 3M KOH and 3M LiOH). Ion intercalation is evidenced by extracting the charge of the double layer, pseudocapacitive and faradaic processes from cyclic voltammograms. It takes place across the entire applied potential window even at scan rates as high as 100 mV.s-1. However, as it is depicted and discussed in this study the amount of charge related to each mechanism depends on the nature of the electrolyte. The highest areal capacitance is 500 µFcm-2 (70 Fg-1) in 3M LiOH. Moreover, after an initial fade the capacitance stabilizes at 90% of the starting value after 5000 cycles, thus opening a new use of transition metal phosphates as electrodes for energy storage devices.