Freestanding MnO2 composite electrode via an in situ growth method for asymmetric sodium-ion capacitor and hybrid capacitive electrodialysis

As a potential energy storage material, Mn-based electrodes have attracted widespread attention in both supercapacitor and capacitive deionization systems. Herein, a freestanding delta-MnO2@rGO/CC composite film is prepared with a simple in situ growth strategy. The asymmetric sodium-ion capacitor consists of delta-MnO2@rGO/CC as cathode and activated carbon (AC) as anode, and demonstrates charge capacity of 77.8 mAh g(-1) at current density of 50 mA g(-1), and the capacitance retention at a current density of 1000 mA g(-1) is close to 100% after 1000 cycles. In addition, the fabricated capacitive electrodialysis cell demonstrates high salt removal capacity of 78, 82, and 152 mg g(-1) under voltage of 1.2, 1.6, and 2.0 V, respectively. Ex situ XRD and XPS measurements are also performed to analyze the Na-storage mechanism of the composite freestanding electrode during the charge and discharge process, indicating its potential application in energy storage and desalination.

Automated summary

In this study, a freestanding delta-MnO2@rGO/CC composite film was prepared using an in-situ growth strategy and applied in a sodium-ion capacitor and capacitive electrodialysis cell, showing good charge capacity and capacitance retention. Ex situ experiments confirmed the Na-storage mechanism of the composite freestanding electrode, indicating its potential application in energy storage and desalination.