Urea-driven hydrothermal synthesis of Mn2O3: electrochemical performance across various electrolytes for supercapacitor applications

In this study, cubic Mn₂O₃ was synthesized using different urea concentrations (3, 6, 9, and 12 mM) via a hydrothermal method. During synthesis, an increase in urea content resulted in decreased particle and crystallite sizes and increased lattice parameters, with a concomitant increase in the surface area and number of Mn³⁺ ions in Mn₂O₃ particles. The electrochemical performance of the Mn₂O₃-9 mM urea sample outperformed samples prepared with other urea contents. The Mn₂O₃-9 mM urea sample exhibited high specific capacitance (C_sp) values in 1 M and 3 M KOH electrolytes, achieving 881.3 F g⁻¹ and 1043.2 F g⁻¹, respectively, at a scan rate of 1 mV s⁻¹. Furthermore, at a current density of 1 A g⁻¹, the C_sp of Mn₂O₃ in 1 M KOH was 758.5 F g⁻¹. The values increased to 891.4 F g⁻¹ with energy density and power density of 44.7 W h kg⁻¹ and 398.1 W kg⁻¹, respectively, in 3 M KOH. Owing to the superior electrochemical performance of the Mn₂O₃-9 mM urea sample, its electrochemical performance was assessed in basic KOH and NaOH and neutral Na₂SO₄ and NaNO₃ aqueous electrolytes. Moreover, the Mn₂O₃-9 mM urea sample demonstrated a C_sp of 721.0 and 446.3 F g⁻¹ in 3 M concentrations of NaOH and NaNO₃ electrolytes, respectively. The Mn₂O₃-9 mM urea sample with the highest content of Mn³⁺ ions displayed the highest C_sp in KOH electrolytes compared with the others owing to the smaller hydration radii of K⁺ and high ionic diffusivity and conductivity of OH⁻ compared with other basic and neutral salts. These results highlight that the synthesis process, electrolyte choice, and concentration of electrolytes significantly influence the electrochemical properties of Mn₂O₃ battery-type, emphasizing their critical role in optimizing material performance for supercapacitor applications.