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

A novel green synthesis strategy-anode glow discharge electrolysis (AGDE) was employed for one-step preparation of α-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 α-MnO₂ with structural defects (oxygen vacancies) is obtained. SEM and TEM revealed that α-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 e_aq ^- 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 α-MnO₂ without adding extra chemicals, and prepared α-MnO₂ can be considered as an excellent candidate of electrode materials for supercapacitor.