V. This suggest that some side reactions start to occur above -1.4 V, and is consistent with our GCD results, which showed slight deviation from the capacitive behavior and larger energy and charge loss at -1.6 V compared to -1.0 V, -1.2 V, and -1.4 V, respectively. The CV at -2.0 V further intensifies the faradaic currents possibly due to undesirable water decomposition and gas evolution reactions. The Nyquist plots from EIS spectra also show capacitive type behavior up to -1.4 V, as seen from their quasi-vertical lines at low frequency. The Nyquist plot at -1.6 V show slight deviation from a quasi-vertical line and the plot at -2 V show a completely redox-type behavior, arguing that the optimal voltage window of GR-AC supercapacitor is -1.4 V for SSA operation.