Fig. 2: Electrochemical properties of UiO-66-(OH)2.
a Cyclic voltammogram of the UiO-66-(OH)2/carbon/PVdF composite electrode in a 0.05 M H2SO4 aqueous solution under Ar atmosphere at the scan rate of 10 mV s−1. As shown in Fig. 2a, a polarization was observed. The previous work reported that the semiquinone state is stabilized at pH < 1, according to DFT calculations, leading to two one-electron oxidation steps rather than a single two-electron step46. In addition, since the conversion of quinone in its neutral state to quinone radical anion was unfavorable, the reduction proceeded via the protonated intermediate46. These factors contributed to the polarization observed in the oxidation process. b Cole-Cole plot of UiO-66-(OH)2. Impedance spectrum of the disk-shaped pellet under 95% RH at 30 °C (Z’: real part, Z”: imaginary part). The flattened semicircles represented the bulk and grain boundary resistances. The crystallinity was maintained even after impedance measurements (Supplementary Fig. 16). c Charging (black)/discharging (red) curves of half-cell using the UiO-66-(OH)2/GMS/PVdF composite electrode at 5 C. Inset: The electrode cycle test (42 C). At 42 C, the UiO-66-(OH)2/GMS/PVdF composite electrode achieved a discharge capacity of more than 90% of the theoretical capacity based on the molecular weight of UiO-66-(OH)2. Therefore, we performed a cycling test at 42 C. d Rate capability of the UiO-66-(OH)2/GMS/PVdF composite electrode (5, 10, 15, 20, 30, and 45 C). Source data are provided as a Source Data file.
