Electrochemical performance of carbon paper supercapacitor using sodium molybdate gel polymer electrolyte and nickel molybdate electrode

Graphene oxide–modified poly (vinyl alcohol)/sodium sulfate-sodium molybdate (GO/PVA-Na2SO4-Na2MoO4, GPSS) gel polymer electrolyte and nickel molybdate (NiMoO4) electrode are integrated to fabricate carbon paper (CP) supercapacitor to improve capacitance performance. GO in PVA gel can introduce an effective ion transport pathway to improve ionic conductivity of gel polymer electrolyte. The ionic conductivity increases from 3.73 mS cm−1 for PVA-Na2SO4 to 6.46 mS cm−1 for GO/PVA-Na2SO4 at optimal GO mass ratio of 0.6% in GO/PVA gel. It also obviously increases from 4.33 mS cm−1 for PVA-Na2SO4-Na2MoO4 to 28.86 mS cm−1 for GO/PVA-Na2SO4-Na2MoO4. Both Na2MoO4 electrolyte and NiMoO4 electrode show reversible redox electroactivity to provide superior pseudocapacitance. Accordingly, the CP supercapacitor using GPSS gel shows specific capacitance of 41.67 mF cm−2 and energy density of 70.02 mWh m−2 at 0.5 mA cm−2, presenting higher performance than 15.91 mF cm−2 and 26.74 mWh m−2 using GO/PVA-Na2SO4 gel. Furthermore, the NiMoO4/CP supercapacitor using GPSS gel shows even higher specific capacitance of 78.18 mF cm−2 and energy density of 131.39 mWh m−2 at 0.5 mA cm−2. It also exhibits high cycling capacitance retention of 85% at 0.5 mA cm−2 for 1000 cycles. The improved capacitance performance of CP supercapacitor using Na2MoO4 gel polymer electrolyte and NiMoO4 electrode is ascribed to reversible redox reaction of Mo(VI)/Mo(V), Mo(VI)/Mo(IV), and Ni(II)/Ni(III). The NiMoO4/CP supercapacitor using GO/Na2MoO4 gel polymer electrolyte becomes desirable for the promising application in energy storage devices.