The impact of overpotential on the enthalpy of activation and pre-exponential factor of electrochemical redox reactions

The kinetics of the V5+/V4+ redox reaction is investigated in a three-electrode configuration on a Vulcan XC-72 modified glassy carbon rotating disk electrode at four different temperatures (25 to 40 degrees C, with 5 degrees C interval). The values of enthalpy of activation (Delta H-#) and pre-exponential factor (A(f)) estimated using the Eyring equation are in the range of 0.25-0.53 eV (24-51 kJ mol(-1)) and -1.3 to 5, respectively. The Eyring plots tend to diverge with overpotential, causing an increase in the values of the estimated Delta H-# and A(f). This is perhaps due to the retarding effect of the precipitates/adsorbates on the electrode surface. The investigation of the kinetics suggests that the V5+/V4+ redox reaction is electrocatalysed through an increase in the entropy of activation (Delta S-#).