Fabrication of manganese oxide electrodes by radio frequency sputtering for electrochemical capacitors

Abstract

Manganese oxide thin films were sputtered on graphite foils by radio frequency (RF) sputtering. At the 1,000th cycle of potential cycling, maximum mass specific capacitance of 341 F g−1 was obtained in 0.5 M LiCl and with optimum sputtering conditions (5 sccm of oxygen, 20 mTorr, and 70 W) as well as annealing temperature (150 °C). These show its high electrochemical stability and good mass specific capacitance at a higher sweep rate of 100 mV s−1. In addition, the higher the volume flow rates of oxygen, the larger the amount of trivalent manganese oxide and the higher the surface roughness, the higher the mass specific capacitance at lower volume flow rates of oxygen, but the amounts of trivalent manganese oxide were almost the same and the mass specific capacitance decreased due to decreasing surface roughness at higher volume flow rates of oxygen. Furthermore, the geometric specific capacitance increases with increasing sputtering pressure and power.