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

Abstract

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.