Electrochemical response of a high-power asymmetric supercapacitor based on tailored MnOx/Ni foam and carbon cloth in neutral and alkaline electrolytes

Tailored 3D Ni foams with smaller macropores and larger surface areas than commercial Ni foams are prepared by electrodeposition under the dynamic hydrogen bubble template on stainless steel substrates. These Ni foams are functionalized with electrodeposited manganese oxide (MnOx), resulting in MnOx/Ni foam composites. The electrochemical performance of the composites is studied in aqueous Na2SO4 and KOH electrolyte. Moreover, asymmetric cells, combining the MnOx/Ni foam composites as positive electrodes and carbon cloths as negative electrodes, are tested in the presence of the two electrolytes. Despite the significant number of papers dealing with asymmetric supercapacitors, there is still the need of understanding the electrolyte role for optimizing their electrochemical response. The cell potential window is broader in neutral electrolyte, 1.6 V, compared to the alkaline one, 1.2 V, but the cell capacitance is lower in the neutral electrolyte, 37 F g(-1), than in the alkaline one, 49 F g(-1). The energy density is similar for the two electrolytes, ca. 10 Wh kg(-1). The power density reaches 1-3.10(4) W kg(-1), which is among the highest values reported for asymmetric cells in aqueous electrolytes. The stability of the cells on cycling, floating and self-discharge are compared for the two electrolytes.