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Electrosynthesis of peroxodiphosphate ions (P2O84−) was performed in 2m K3PO4, 1m K2HPO4 medium, using a platinum anode. The results showed that under conditions of potentiostatic polarization at constant potential, the reaction rate reaches a maximum value of 125mAcm−2 and a faradaic yield of 30%. From about 1.9V, the reaction kinetics are increasingly inhibited as the potential shifts positively. Rapid scanning potential voltammetry was used to characterize the oxidation state of the electrode surface. This method shows that the growth of α (PtO) and β (PtO2 or PtO3) oxides depend on the applied potential. It also establishes a correlation between the inhibition of P2O84− ion electrosynthesis and the β oxide coating surface. When 2×10−3m KSCN is added to the solution, some oxygen evolution sites are selectively blocked and β oxide occurs at more positive potential values. Consequently, the rate of peroxodiphosphate ion formation and the faradaic efficiency are increased to 380mAcm−2 and 75%, respectively. Under pulsed potential conditions it was possible to reach 1200mAcm−2 for P2O84− ion electrosynthesis with a faradaic yield of 82%. |
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