Controlled Hydrothermal Growth of α‐MnO ₂ Nanorods: Effect of Temperature on Electrochemical Performance

Abstract This study reveals that the structural, morphological, and electrochemical properties of α‐MnO 2 nanomaterials can be effectively tuned by varying the hydrothermal synthesis temperature. Samples were synthesized at 120, 140, and 160 °C. XRD confirmed the formation of a pure tetragonal α‐MnO 2 phase at higher temperatures, with improved crystallinity. SEM and TEM images revealed a transition from agglomerated particles to well‐defined, uniform nanorods at 160 °C. Raman analysis of M‐160 showed characteristic α‐MnO 2 bands, with strong 574 cm −1 peak confirming Mn‐O vibrations in MnO 2 octahedra and predominance of Mn 4+ species. XPS analysis verified the dominance of Mn⁴⁺ oxidation state, confirming the formation of α‐phase MnO 2 . Thermal analysis showed good thermal stability up to around 300 °C. M‐160 showed the highest surface area (55.3 m 2 /g) with mesoporosity (3.03 nm). Electrochemical characterizations including CV, GCD, and EIS revealed that the sample synthesized at 160 °C exhibited the best performance, with a high specific capacitance of 471.37 F/g at 10 mV/s and 460.4 F/g at 1 A/g. The assembled device delivered a power density of 2.08 kW/kg and energy density of 55.92 Wh/kg. These findings suggest that α‐MnO 2 synthesized at 160 °C is a promising electrode material for high‐performance supercapacitor applications.