Anode Glow Discharge Electrolysis Synthesis of Flower‐Like α ‐MnO 2 Nanospheres: Structure, Formation Mechanism, and Supercapacitor Performance

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.