3.2 The Electrochemical Performance of ZMOP Cathode
To investigate the performance of ZMOP-x nanowires cathode, the Zn//ZMOP-x was assembled in the mixed aqueous solution of ZnSO4 (2 M and 0.1 M ) with metal Zn anode and ZMOP-x cathode. Figure 6a exhibits the CV properties of Zn//ZMOP-x at different speeds (0.5, 1.0, 2.0, 3.0, 4.0, 5.0 mVs-1) and the voltage window is 0.8-1.9V. It can be found that the ZMOP-4 nanowires have a pair of main redox peaks near 1.746/1.312V. The emergence of peaks could correspond to the deintercalation and intercalation of Zn2+ ions, which are concomitant with the oxidation and reduction reaction of the Mn +3 state. Through the rate capabilities of the ZMOP-x electrode with various PPy doping amounts, it can be found from Figure 6b that under different current densities, the ZMOP-4 electrode shows the best rate performance (156.4, 129.4, 84.7, 66.5, 53.2, 38.19 mAh g-1). Because of the proper addition of PPy, it improves the electrical conductivity, thus accelerating the electron transfer of Zn2+, so it has excellent magnification performance. The rate performance of the ZMOP-6 electrode (156.4, 129.4, 84.7, 61.5, 45.6, 29.2 mAh g-1) is similar to the ZMOP-4 at low current densities region. Nevertheless, with the increasing current density, the capacity of the ZMOP-6 electrode is decreasing. Therefore, the most suitable cathode material should be ZMOP-4 nanowires. Figure 6c shows the EIS curves of the as-prepared materials. It was tested in the open circuit potential range of 100 kHz~0.01 Hz. They all show low charge transfer resistance in the high-frequency region. While ZMOP-4 electrode has relatively low charge transfer resistance and a larger curve slope, indicating that the ZMOP-4 electrode has the strongest ability to rapidly diffuse ions. The pseudo-capacitance contribution of Zn//ZMOP-4 is calculated in Figure 6d , and the pseudo-capacitance contribution can reach 71.8% when the sweep speed reaches 5.0 mVs-1. Figure 6e shows that ZMOP-4 nanowires exhibit outstanding cycle stability. After 5000 cycles at 0.2 A g-1, the capacity retention still maintains at 82.6%, and the equivalent coulombic efficiency is 99.7%.