In situ mass change and gas analysis of 3D manganese oxide/graphene aerogel for supercapacitors†
Manganese oxide nanoparticles decorated on 3D reduced graphene oxide aerogels (3D MnOx/rGOae) for neutral electrochemical capacitors were successfully produced by a rapid microwave reduction process within 20 s. The symmetric electrochemical capacitor of 3D MnOx/rGOae (Mn 3.0 at%) storing charges via both electric double layer capacitance (EDLC) and pseudocapacitance mechanisms exhibits a specific capacitance of 240 F g−1 as compared with 190 F g−1 of that using the bare 3D rGOae at 0.5 A g−1 in 1 M Na2SO4 (aq.) electrolyte. It retains 90% of the initial capacitance after 10 000 cycles, demonstrating high cycling stability. In addition, the charge storage mechanism of 3D MnOx/rGOae was investigated using an electrochemical quartz crystal microbalance. In situ gas analysis using differential electrochemical mass spectrometry (DEMS) shows the CO2 evolution at a cell potential over 1 V indicating that the positive electrode is possibly the voltage limiting electrode in the full cell. This finding may be useful for further development of practical high power and energy supercapacitors.