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 overpotential 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 overpotentials, 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