Anode Glow Discharge Electrolysis Synthesis of Flower-Like α-MnO2 Nanospheres: Structure, Formation Mechanism, and Supercapacitor Performance

Graphical Flower-like α -MnO 2 nanospheres with assembled by dozens of nanosheets were fabricated using KMnO 4 as precursor via anode glow discharge electrolysis (AGDE), and then employed as a positive electrode material of supercapacitor to successfully light the light-emitting diode (LED). A novel green synthesis strategy–anode glow discharge electrolysis (AGDE) was employed for one-step preparation of α -MnO 2 in 2 g L −1 KMnO 4 solution, in which Pt needle and carbon rod were regarded as anode and cathode, respectively. The optimal preparation condition is 400 V for 60 min and the power consumption is below 45 W. The XRD, Raman spectra, XPS and EPR proved that α -MnO 2 with structural defects (oxygen vacancies) is obtained. SEM and TEM revealed that α -MnO 2 shows a flower-like nanospheres with a diameter of 165 nm, which is assembled by many nanosheets. A possible formation mechanism is that the MnO 2 is generated via the reduction of MnO 4 − by H⋅ and e aq − in plasma-liquid interface. Electrochemical test found that MnO 2 nanospheres exhibit a specific capacitance of 365 F g −1 at 1 A g −1 , and capacity retention of 79.8 % after 10,000 cycles at 5 A g −1 . The assembled asymmetric supercapacitor shows the maximum energy density of 23.1 Wh kg −1 at power density of 1.89 kW kg −1 . In brief, AGDE is a simple, facile and green technique for the synthesis of α-MnO 2 without adding extra chemicals, and prepared α -MnO 2 can be considered as an excellent candidate of electrode materials for supercapacitor.