Electrochemical workstation

To perform the electrochemical measurements, an electrochemical workstation (Metrohm Autolab B.V., Utrecht, The Netherlands) was used with a three-electrode configuration, where the as-prepared CoO_x-rGO, Hg/HgO and Pt wire were working, reference and counter electrodes, respectively. The electrochemical measurements included the cyclic voltammetry (CV), galvanostatic charge–discharge test (GCD) and electrochemical impedance spectroscopy (EIS). CV measurements were performed at different scan rates from 10 to 100 mV/s in the potential window of 0–0.6 V. The GCD tests were carried out in the same potential window and at various applied current densities. The EIS measurements were recorded in a frequency range of 100 kHz to 10 mHz with an ac perturbation signal of 10 mV. All the electrochemical measurements were carried out in 1 M KOH aqueous electrolyte in ambient conditions at room temperature (23 °C). The electrochemical measurements setup was constructed using the PTFE (Teflon) rod (McMaster-Carr, Elmhurst, IL, USA), and it is schematically shown in Figure 2.

Differential pulse voltammetric (DPV) measurements were carried out on an Autolab Electrochemical Workstation (Metrohm, Switzerland) with a conventional three-electrode system: an ITO electrode as the working electrode, a platinum wire as the counter electrode, and an Ag/AgCl electrode as the reference electrode. It should be noted that ITO electrode with negative charge was obtained by using a previously reported pretreatment method^{29 (link)}.