Anode glow discharge electrolysis synthesis of flower‐like α‐MnO2 nanospheres: structure, formation mechanism, and supercapacitor performance

A novel green synthesis strategy—anode glow discharge electrolysis (AGDE) was employed for one‐step preparation of a‐MnO2 in 2 g L‐1 KMnO4 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 a‐MnO2 with structural defects (oxygen vacancies) is obtained. SEM and TEM revealed that a‐MnO2 shows a flower‐like nanospheres with a diameter of 165 nm, which is assembled by many nanosheets. A possible formation mechanism is that the MnO2 is generated via the reduction of MnO4− by H· and eaq− in plasma‐liquid interface. Electrochemical test found that MnO2 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 a‐MnO2 without adding extra chemicals, and prepared a‐MnO2 can be considered as an excellent candidate of electrode materials for supercapacitor.