Oxygen vacancy enriched Na+ intercalated MnO2 for high-performance MXene (Ti3C2Tx)-based flexible supercapacitor and electrocatalysis

Abstract

The increased interest in smart and portable electronic gadgets has led to the development of flexible and wearable energy storage systems. Herein, the oxygen vacancy-enriched Na-MnO2-x is synthesized using a simple, scalable, and inexpensive electrodeposition method. The oxygen vacancy enrichment effectively enhances the conductivity and reaction kinetics of the Na-MnO2 electrode. The Na-MnO2-x film electrode reveals an excellent specific capacitance of 395 F g−1 at the scan rate of 5 mV s−1 with high capacitance retention of 85.9 % after 10,000 cycles at a current density of 5 A g−1. To verify the practicability, three asymmetric supercapacitors (ASCs) (Mn3O4//Ti3C2Tx, Na-MnO2//Ti3C2Tx, and Na-MnO2-x//Ti3C2Tx) are fabricated and their respective performances are contrasted. The Na-MnO2-x//Ti3C2Tx ASC reveals a maximum energy density of 25 Wh kg−1 at the power density of 1000 W kg−1, along with excellent capacitance retention of 98.8 % after 10,000 cycles. In addition, to validate the suitability of Na-MnO2-x electrode for flexible energy storage, the flexible Na-MnO2-x//Ti3C2Tx ASC is fabricated that operates in the potential window of 2 V in PVA: Na2SO4 polymer gel electrolyte and delivers a high volumetric energy density of 510.3 mWh cm−3 at a power density of 40,483 mW cm−3. Moreover, the electrocatalytic activity of Na-MnO2-x thin films reveals an overpotential of 439.7 and 381.2 mV to drive a current density of 10 mA cm−2 corresponding to HER and OER, respectively. Therefore, the electrodeposited, oxygen vacancy-enriched Na-MnO2-x film electrode has great potential to be used for both flexible energy storage and electrocatalysis. © 2024 Elsevier Ltd