The voltage-dependent electrochemical impedance spectroscopy of CoCrMo medical alloy using time-domain techniques: Generalized Cauchy–Lorentz, and KWW–Randles functions describing non-ideal interfacial behaviour

In this study, we examined the change of interfacial properties of a CoCrMo biomedical alloy (ASTM F-1537) in phosphate-buffered saline (PBS) (pH 7.4) at different voltages. Step polarization impedance spectroscopy technique was used to apply 50 mV voltage steps to samples, and the time-based current transients were recorded. A new equation is derived based on capacitive discharge through a Tafel element and generalized to deal with non-ideal impedance behaviour. The new function compared to the KWW–Randles function, better matches the time-transient response. The results also show a voltage-dependent oxide resistance and capacitance behaviour.

Research highlights
► A new function was developed to model the current response in the time domain.
► Voltage-dependant oxide resistance and capacitance was observed for CoCrMo alloy.
► Impedance parameters show a distinctive change at +250 mV (Ag/AgCl).