Enhanced Supercapacitive Performance of MnCO 3 @rGO in an Electrolyte with KI as Additive

MnCO 3 @rGO (GM) was synthesized through a facile one‐pot hydrothermal process with graphene oxide and KMnO 4 as precursors. X‐ray diffraction analysis reveals that the prepared MnCO 3 possesses a high crystallinity with a grain size of 28.4 nm. To improve the capacitive performance of GM, KI was added to the Na 2 SO 4 electrolyte as a redox additive. Electrochemical measurements show that the specific capacitance of GM in KI additive electrolyte could reach up to 546 F g −1 at the current density of 0.5 A g −1 . This value is 8 times larger than that (61 F g −1 ) in Na 2 SO 4 electrolyte at the same current density. The elevated specific capacitance is attributed to the presence of I − , which can bring about significant pseudocapacitance through the redox couples of I − /I 3 − and I − /IO 3 − as confirmed by X‐ray photoelectron spectroscopy. GM also possesses a capacitance retention ratio of around 103 % after 2000 cyclic voltammetry measurements, suggesting a superior cycling stability.