Green Strategy for the Synthesis of K plus Pre-inserted MnO2/rGO andIts Electrochemical Conversion to Na-MnO2/rGO for High-Performance Supercapacitors

an eco-friendly and low-cost green strategy hasopted to synthesize K+ion pre-inserted MnO2(K-MnO2) and itshybrid with reduced graphene oxide (K-MnO2/rGO) nanostruc-tures using aloe vera leaf extract (an effective reducing and cappingagent). K-MnO2and K-MnO2/rGO hybrid formations wereconfirmed by X-ray diffraction, Raman, and X-ray photoelectronspectroscopy measurements. The K-MnO2/rGO hybrid was foundto be a better electrode material for supercapacitor application. Byperforming cyclic voltammetry measurements in 1 M Na2SO4electrolyte solution, we found that the K+ions present inside theMnO2structure get replaced by the Na+ions present in theelectrolyte leading to Na+ion inserted MnO2(Na-MnO2)formation. The phase transformation of K-MnO2/rGO to Na-MnO2/rGO was confirmed using Raman and XPS analyses. This electrochemical phase transformation by Na+ion intercalationimproves the overall supercapacitive performances. It was revealed that, during the electrochemical cyclic process, the specificcapacitance values of the K-MnO2/rGO hybrid hiked more than 4 times due to Na+ion intercalation. The possible conversionmechanism of K-MnO2to Na-MnO2is provided. Fabrication of an asymmetric supercapacitor of Na-MnO2/rGO//activated carbondisplays a high operating potential window of 2.2 V, a maximum energy density of 44.4 W h kg-1, and a power density of 8.79 kWkg-

Automated summary

A green strategy using aloe vera leaf extract was adopted to synthesize K+ion pre-inserted MnO2 and its hybrid with reduced graphene oxide, leading to improved supercapacitive performance through Na+ ion intercalation.