2014 Volume 122 Issue 1426 Pages 426-429
Electrochemical properties of layer-structured H2W2O7 for electrochemical capacitors were investigated in an aqueous electrolyte for the first time. H2W2O7 was synthesized from Bi2W2O9 by proton-exchanges with acid treatment. H2W2O7 exhibited a low redox potential of about −0.3 V in a H2SO4 electrolyte solution. The H2W2O7 electrode showed an oxidation capacity of 56 mAh g−1 at a current density of 300 mA g−1, which is equal to the theoretical capacity assuming that 0.5 electrons react with one tungsten ion. H2W2O7 also retained 88% oxidation capacity at a high current density of 2 A g−1 against that at a low current density of 300 mA g−1. It is assumed that redox reaction rate mainly depends on proton diffusion in H2W2O7. Moreover, this material showed excellent cycle stability over 1000 cycles without capacity loss. It is clarified that a H2W2O7 electrode is a promising electrode for electrochemical capacitors featuring a high rate capability and good cycle life.