Strategic harmonization of surface charge distribution with tunable redox radical for high-performing MnO2-based supercapacitor

The intercalation capacitance in MnO2-based supercapacitor gives rise to a higher energy density compared with the traditional supercapacitors. However, the ion intercalation process was greatly influenced by the surface charge distribution in the electrode. Optimizing the MnO2 surface charges for facilitating electrolyte ions intercalation/deintercalation becomes an effective way to improve the performance of supercapacitors. Herein, a harmonization effect was achieved between the electrolyte ion and surface charge of the typical MnO2-based electrode. In the experiment, by introducing redox radical 4-Hydroxy-2, 2, 6, 6-tetramethyl-piperidinooxy (HTEMPO) into the electrolyte, dissolved Mn2+ combines with negative-charged HTEMPO - groups and forms an electrically neutral region during discharging, which significantly weakens the electrostatic repulsion effect of Mn2+ on electrolyte ions and enhances the intercalation of Na+ effectively. Such an electrochemical mechanism was carefully studied and confirmed by combining the electrochemical impedance and electrochemical quartz crystal microbalance. The resulted electrode delivers superior electrochemical performance with a specific capacitance of 773 F/g, which is about 220% higher than that without HTEMPO (similar to 357 F/g). Besides, the proportion of intercalation capacitance increases by similar to 3.3 times after adding HTEMPO, reaching 64.2% compared with that of 19.3% without HTEMPO. It is believed that the novel strategy proposed in this work will be greatly beneficial for the development of high-performance supercapacitors. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The optimization of MnO2 surface charges facilitates electrolyte ions intercalation/deintercalation, improving the performance of supercapacitors. The introduction of redox radical HTEMPO weakens the electrostatic repulsion effect of Mn2+ on electrolyte ions, enhancing the intercalation of Na+ efficiently.