K⁺-Intercalated MnO₂ Electrode for High Performance Aqueous Supercapacitor

MnO2 is often considered to be a promising supercapacitor electrode due to its unique electrochemical properties. This is largely due to the various arrangements of the corner and edge sharing MnO6 octahedra that form a variety of sublattices. Not only do the interstitial sites that are generated in this process allow the occupancy of alkali, alkali earth cations, and water to stabilize the MnO2 framework but also the process itself requires energy which is competitive against probable oxygen evolution reaction. Owning to its higher mobility and higher conductivity as compared to common alkali cations such as Li+ and Na+, K+ was selected as the intercalating cation to form K0.6MnO2 and it was used as positive electrode. When paired with K+-adsorbed holey carbon as the negative electrode, the 2.4 V asymmetric aqueous supercapacitor was able to deliver 52.8 Wh kg–1 and power density of 58.4 kW kg–1. A good cyclic life of ca. 95% capacitance retention was also demonstrated after cycling for 10000 cycles at 20 A g–1.