Electrochemical measurements were partly performed on a CHI 660C electrochemical workstation (Shanghai Chenhua Instrument Corporation, China) with a conventional three electrode cell. The OMC/GCE or GCE, an Ag/AgCl electrode (KCl saturated) and a piece of Pt wire were served as working, reference and counter electrode, respectively. Electrochemical impedance spectroscopy (EIS) experiments were performed on a PARSTAT 2273 potentiostat and the transmission electron microscopy (TEM) image was recorded on a JEM-2100F transmission electron microscope (JEOL, Japan) operating at 200 kV. Moreover, the sample solutions were purged with purified nitrogen for 20 min to remove oxygen prior to the beginning of a series of experiments.