Ultraslow kinetics of the ferric/ferrous electron transfer reaction on Au(110) electrode in perchloric acid solutions

Rotating disk electrode voltammetry is used to study kinetics of the ferric-ferrous redox reaction on an Au(110) electrode in purified perchloric acid solutions. The reaction is characterized by an apparent standard rate constant of about 10(-6) cm s(-1), which is far lower than the values reported for polycrystalline gold electrodes. Contrary to expectations, the rate constant depends only weakly on the perchloric acid concentration ranging from 0.01 to 0.5 mol dm(-3). Analysis of kinetic data suggests that the ion reaction site is shifted out of the diffuse double layer due to the competition between the increase of the ferric ion distribution function and the decrease of the electron transfer probability, which both depend on the magnitude of the electric field. Effect of the electrode material on the apparent standard rate constant is proposed to be due to a difference in the density of electronic surface states rather than in the potential of zero charge. Strong catalysis by gold surface oxides and by chlorides present in the solution at concentrations ranging from 1.8 x 10(-7) to 7.2 x 10(-7) mol dm(-3) is demonstrated. (C) 1999 The Electrochemical Society. S0013-4651(98)11-032-7. All rights reserved.