Anomalous effect of K ion on crystallinity and capacitance of the manganese dioxide

► Describe a fundamental study which correlates K+ has the anomalous effect on MnO2 crystalline state and capacitance.► Adding K+ not only delayed the conversion of MnO2 crystalline, but also delayed the phase transformation temperature. ► The specific capacitance value big difference from 58 F g−1 for H2/400 to 124 F g−1 for K12/400. ► These results have important implications for the characterization of MnO2 in catalysis and supercapacitor applications.