Pulse electrodeposition of manganese oxide for high-rate capability supercapacitors

Two kinds of manganese oxide films (denoted as p-MnO_x and g-MnO_x) were electrodeposited on graphite substrate by the pulse current or galvanostatic methods, respectively. The g-MnO_x showed Mn₃O₄ characteristics and the p-MnO_x exhibited a mixture of Mn₃O₄ and MnOOH phase from XRD pattern and Raman spectra. The g-MnO_x showed the capacitance of 160 F g^-1 while p-MnO_x exhibited 252 F g^-1 at the scanning rate of 10 mV s^-1. Interestingly, the retained ratio of capacitance of g-MnO_x was 31% whereas that of p-MnO_x was still 56% when the scanning rate increased to 500 mV s^-1. The high-rate capability of p-MnO_x may be primarily attributed to the improvement in wettability on the interface of electrode/electrolyte, which came from its more amount of hydroxyl, resulting in easier cation ions transport and more accessible active sites.