Ion implantation was used to modify the surface properties of yttria-stabilized material. A 3-electrode cell was used to measure steady-state current versus over-potential curves and to determine the electrode impedance. A 10- to 50-fold increase, in the equilibrium exchange current density at the Au,O2(g)/zirconia interface, was observed after the implantation of 15kV 56Fe ions to a dose of 8 x 1016/cm2. This increase resulted from a broadening of the active surface area due to an increase in the electronic conductivity of the implanted surface and from an increase in the fractional coverage of adsorbed O molecules. The double layer capacitance of the interface increased by a factor of 10 to 100 after implantation. This was thought to be due to the variable oxidation state of the implanted Fe ions; thus providing an additional means for charge accumulation. In comparison with the non-implanted interface, no changes in the rate-determining steps of the O exchange mechanism occurred after Fe implantation. Similar apparent charge-transfer coefficients were determined. The experimental results were explained in terms of a reaction model in which the charge-transfer process competed with the surface diffusion of molecular adsorbed O species along the interface between the noble metal and the solid electrolyte. At cathodic and anodic over-potentials, inductive effects appeared in the impedance diagram at low frequencies. The inductive effects resulted from a charge-transfer mechanism in which a step-wise transfer of electrons to adsorbed O species took place.

B.A.Van Hassel, B.A.Boukamp, A.J.Burggraaf: Solid State Ionics, 1992, 51[3-4], 161-74