Effect of Different Concentrations of KMnO₄ Precursor on Supercapacitive Properties of MnO Thin Films

Abstract

In the present work, the electrochemical performance of MnO thin films synthesized using the different concentrations of KMnO₄ is reported. Structural study confirms the cubic structure of MnO thin films. The contact angle study confirms the hydrophilic nature of the prepared thin films. Surface morphology study reveals highly porous and well-connected uniformly distributed spherical grains. Furthermore, a Brunnauer–Emmett–Teller study reveals the co-existence of mesoporous nature with a pore size of 4 nm having surface area 24.12 m² g⁻¹. Electrochemical supercapacitive property gives the highest specific capacitance of 561 F g⁻¹ at the scan rate 5 mV s⁻¹ in 1 M Na₂SO₄ aqueous electrolyte. The power and energy density for the optimized electrode is 357 W kg⁻¹ and 47 Wh kg⁻¹, respectively, at 0.5 mA current density. The electrochemical impedance spectroscopy spectra of the electrode show the less charge transfer resistance (R_ct) of 1.64 Ω, as compared to other electrodes. The higher cycling stability of 84% is achieved after 1500 cyclic voltammetry cycles. The flexible solid-state MnO//MnO symmetric supercapacitor device exhibited maximum specific capacitance of 117.78 F g⁻¹ at 5 mV s⁻¹. Also, the device possesses high energy and power densities of 23.26 Wh kg⁻¹ and 210 W kg⁻¹, respectively, at 4 mA current density.