Electrochemical properties of the PW

11

Cr(Ⅲ)O

4-

39

(PW

11

Cr) in H

3

PO

4

-HAc-H

3

BO

3

(pH 2.16) buffer were investigated in detail by cyclic voltammetry

AC voltammograms and alternating current impedance analyses. The result of cyclic voltammogram showed that three pairs of redox waves were observed on the glassy carbon (GC) electrode in H

3

PO

4

-HAc-H

3

BO

3

(pH 2.16) buffer solution containing 1.0 mmol12539;L

-1

PW

11

Cr. The pair of quasireversible wave at 1.30/0.631 V belonged to Cr(Ⅴ)/Cr(Ⅲ) two-electron redox

while the two pairs of reversible waved at -0.553/-0.505 V and -0.782/-0.725 V belonged to W-O skeleton twoelectron redox. When the pH value increased

the peak potential of the three pairs of twoelectron waves shifted negatively and the peak current decreased

which showed that H

+

was involved in the electrode process. In addition

the difference of peak potential between anode and cathode for each pair of waves increased

which showed reversibility of electrode process decreased. The diffusion coefficient

D

O

of PW

11

Cr calculated from linear relationship of peak current of the first skeleton reduction wave versus square root of potential scan rate was 4.4×10

-6

cm

2

·s

-1

in H

3

PO

4

-HAc-H

3

BO

3

(pH 2.16)buffer. AC impedance of Cr (Ⅲ) was a semicircle without Wahlberg line occurred at high frequency

which showed the anode oxidation process was controlled by heterogeneous charge transfer dynamics. The dynamic parameter

k

o

of electrode process was calculated from the relationship between phase angle and frequency. AC impedance of PW

11

Cr keleton reduction revealed the electrode process was controlled by diffusion.