The EIS experiments were carried out at 0.55 V bias in the dark using an electrochemical workstation (PGSTAT. 302N, Autolab, Eco-Chemie, The Netherlands) with a conventional three electrode cell system at room temperature. The measured frequency range was from 100 mHz to 1 MHz, and the AC amplitude was set at 10 mV. The analysis of EIS data was performed using Zview/Zplot
(Scribner Associates, Inc.) on the basis of Macdonald’s algorithm (LEVM 7), applying a complex non-linear least square (CNLS) approximation method.