Time-optimized ultrasonic synthesis of α-MnO₂ nanoflower: controlling structural evolution and agglomeration for...

This study presents a simple ultrasonication-assisted route for the synthesis of α-MnO₂ nanoflowers at room temperature. The process employs acoustic cavitation at 40 kHz and 100 W with test synthesis times of 0, 20, 40, and 60 min. The best results were obtained with 40 min of sonication, yielding uniform nanoflower structures with (2 × 2) tunnel framework of α-MnO₂, a maximum specific BET surface area of 182 m² g^-1 and total pore volume of 0.41 cm³ g^-1. Besides, the electrochemical measurements of α-MnO₂ nanoflowers were carried out using a three-electrode configuration, achieving a specific capacitance of 121F g^-1 in 1 M Na₂SO₄ and 116F g^-1 in 1 M LiCl electrolytes at 2 mV s^-1 for 40 min sonicated sample. Moreover, the electrochemical impedance spectroscopy indicates notable reduction in the charge transfer resistance upon optimization. The fabricated symmetric device exhibits a coulombic efficiency of ∼99% over 10,000 cycles in a 1 M Na₂SO₄ electrolyte. The ambient, template-free synthesis condition offer clear pathways to industrial scalability. This work establishes sonication duration as a versatile parameter for engineering metal oxides with tailored morphology, delivering reliable performance and long-term stability in neutral aqueous supercapacitors.