Layered Vanadium Phosphates as Electrodes for Electrochemical Capacitors Part I: The Case of VOPO 4 ·2H 2 O

VOPO4 center dot 2H(2)O was synthesized and investigated as an electrode material for electrochemical supercapacitors. The electrochemical characterizations were performed in three different electrolytes (3M LiNO3, 3M KOH and 3M LiOH). Ion intercalation is shown by extracting the charge of the double layer, pseudocapacitive and faradaic processes from cyclic voltammograms. This takes place across the entire applied potential window even at scan rates as high as 100 mV.s(-1). However, the amount of charge related to each mechanism depends on the nature of the electrolyte. The highest areal capacitance is 500 mu F cm(-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.