Facile synthesis of mesoporous MnO2 microspheres for high performance AC//MnO2 aqueous hybrid supercapacitors

• A facile and scalable chemical deposition method was proposed.
• The MnO2 microspheres exhibit large specific surface area and mesopore volume with high tap density.
• The AC//MnO2 capacitor exhibits large specific capacitance, high rate capability and excellent cycling behavior.
• The concept of micro-/nano-characteristics materials was stressed.

Mesoporous manganese oxides (MnO2) microspheres were synthesized by the first chemical deposition of manganese carbonate (MnCO3) precursors at room temperature and followed by the low-temperature calcinations under 300, 350 and 400 °C. The obtained MnO2 materials exhibit the Akhtenskite type MnO2 crystalline microstructures and the microspherical morphologies with the diameter of about 1 μm. The as-synthesized MnO2 microspheres under 300 °C exhibit the largest specific area (240.5 m2 g−1) and the optimal mesopore volume (0.231 cm3 g−1) than the other two samples under 350 and 400 °C (111.4, 106.3 m2 g−1; 0.055, 0.021 cm3 g−1), which contribute to the optimal electrochemical performances for supercapacitors. Moreover, the as-synthesized MnO2 microspheres under 300 °C possess the highest tap density (1.156 g cm−3) than the other two samples (1.126, 1.043 g cm−3), leading to the more feasibility for practical applications in supercapacitors. The as-fabricated MnO2 electrode exhibits a high specific capacitance (129 F g−1 at 0.25 A g−1) and high-rate capability (68 F g−1 at 4 A g−1). The as-assembled activated carbon (AC)//MnO2 hybrid capacitor exhibits a wide working voltage (1.8 V), high power and energy densities (2197 W kg−1 and 12.8 W h kg−1 at 4 A g−1), excellent cycling behavior (94.3% capacitance retention after 5000 cycles at 1 A g−1), and excellent capacitance recovery performances under different rates (0.25–4 A g−1) for tested 4500 cycles, indicating the promising prospective of the easily fabricated mesoporous MnO2 microspheres for practical applications in supercapacitors.