Synthesis of δ-MnO₂ with nanoflower-like architecture by a microwave-assisted hydrothermal method

By a microwave-assisted hydrothermal method, nanoflower-like δ-MnO₂ was prepared for application in supercapacitors as electrode material. The characterization results indicated that the obtained architecture had the characteristics of electrode materials with high electrochemical performance. The flower architecture provided the channel surrounded by the nanosheets-like petals for the fast transfer of electrolyte ions. The thin thickness of nanosheets minimized the diffusion distance of electrolyte ions beneath the surface of material particles. The two advantages of the material guaranteed the high performance of material. It presented specific capacitance of 328 F g⁻¹ at 5 mV s⁻¹ in 1 M Na₂SO₄ aqueous solution within a wide potential window of −0.5~1.0 V. During cycle stability test, the capacitance of material still remained 89% of its initial value after 5000 charge–discharge cycles. These results demonstrated that the nanoflower-like δ-MnO₂ could be applied as high performance electrode material.

MnO₂ with different crystallographic forms and architectures was prepared by normal hydrothermal and microwave-assisted hydrothermal methods, respectively. The α-MnO₂ prepared by normal hydrothermal method presented architecture of nanobundles and the δ-MnO₂ prepared by microwave-assisted hydrothermal method exhibited architecture of nanoflower. The results of electrochemical measurements indicated that δ-MnO₂ had the higher performance than α-MnO₂ due to its unique nanoflower architecture.