Enhanced Cycle Performance of MnO2 Supercapacitors By Ultrasonic-Assisted Electrodeposition

Abstract

Among the various inexpensive and environmentally friendly candidates for supercapacitors, MnO2 has been investigated extensively due to its outstanding comprehensive performance. However, MnO2 exhibits poor cycle performance in many research work, which may possibly due to the dissolution of MnO2 during charge-discharge cycles. In this work, we report a facile and effective method to improve the cycle performance of MnO2 films by ultrasonic-assisted electrodeposition. The MnO2 films were electrodeposited on Ni foam substrates without treatment (denoted as sample I), with post-ultrasonic treatment (denoted as sample II) and synchro-ultrasonic treatment (denoted as sample III). The structures of the MnO2 films are characterized by SEM and TEM. MnO2 nanowire clusters and nanosheet arrays can be observed in the samples prepared by post-ultrasonic assisted and synchro-ultrasonic assisted electrodeposition, respectively, while irregular nanosheets are inspected in the samples without ultrasonic assistance. The electrochemical testing of cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) measurements show typical pseudocapacitive behaviors for all samples. Directly electrodeposited MnO2 film without ultrasonic assistance suffers from obvious attenuation in capacitance, which decreases about 37% from 230 F g-1 in 3000 cycles. Comparatively, the ultrasonically treated MnO2 films exhibit a maximum specific capacitance of 369 F g-1 and 325 F g-1 at 1 A g-1, respectively, which can maintain 98% and 86% up to 3000 cycles, respectively. The effects of the deposition current and ultrasonic time were also investigated. The enhancement in electrochemical performance is significant for the samples with ultrasonic-assisted treatment, suggesting the treated MnO2 films to be a promising choice for supercapacitors. Figure 1