Facile hydrothermal synthesis of α-MnO2 and δ-MnO2 for pseudocapacitor applications

We report the comparison of the electrochemical performances of alpha-MnO2 and delta-MnO2 produced by hydrothermal treatment. The structure and morphology of these materials were analyzed by SEM, HRTEM, XRD, and XPS, while their electrochemical properties were tested in the 1 M Na2SO4 aqueous electrolyte by cyclic voltammetry, galvanostatic charge-discharge measurements, and electrochemical impedance spectroscopy. The specific capacitance of delta-MnO2 at 1 mV.s(-1) was 4.8 times higher than that of alpha-MnO2 (211 vs. 44 F.g(-1)) because of the layered structure of delta-MnO2 that provided better availability of the electrode surface for electrolyte ions during charge-discharge cycles and pseudocapacitance behavior attributed to faradaic redox reactions. Moreover, delta-MnO2 revealed high electrochemical stability (more than 98% of the initial capacitance after 5000 charge/discharge cycles) confirming its good performance as an electrode material for pseudocapacitors. The contributions of surface and diffusion capacitances were analyzed by the differentiation method.

Automated summary

In this study, the electrochemical performances of hydrothermally treated α-MnO2 and δ-MnO2 were compared. The results showed that δ-MnO2 had a higher specific capacitance than α-MnO2, attributed to its layered structure and pseudocapacitance behavior. Additionally, δ-MnO2 exhibited high electrochemical stability, making it a suitable electrode material for pseudocapacitors.