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Performance, stability and operation voltage optimization of screen-printed aqueous supercapacitors

View Article: PubMed Central - PubMed

ABSTRACT

Harvesting micropower energy from the ambient environment requires an intermediate energy storage, for which printed aqueous supercapacitors are well suited due to their low cost and environmental friendliness. In this work, a systematic study of a large set of devices is used to investigate the effect of process variability and operating voltage on the performance and stability of screen printed aqueous supercapacitors. The current collectors and active layers are printed with graphite and activated carbon inks, respectively, and aqueous NaCl used as the electrolyte. The devices are characterized through galvanostatic discharge measurements for quantitative determination of capacitance and equivalent series resistance (ESR), as well as impedance spectroscopy for a detailed study of the factors contributing to ESR. The capacitances are 200–360 mF and the ESRs 7.9–12.7 Ω, depending on the layer thicknesses. The ESR is found to be dominated by the resistance of the graphite current collectors and is compatible with applications in low-power distributed electronics. The effects of different operating voltages on the capacitance, leakage and aging rate of the supercapacitors are tested, and 1.0 V found to be the optimal choice for using the devices in energy harvesting applications.

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(a) Initially measured capacitances of samples measured at different voltages, plotted against AC ink mass. Each data point is a different sample. (b) Change in capacitance after cycling and after voltage hold at different voltages; separate sample batches were used for the cycling and the hold. (c) Leakage current at different voltages initially (all samples), after cycling and after voltage hold (separate samples).
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f6: (a) Initially measured capacitances of samples measured at different voltages, plotted against AC ink mass. Each data point is a different sample. (b) Change in capacitance after cycling and after voltage hold at different voltages; separate sample batches were used for the cycling and the hold. (c) Leakage current at different voltages initially (all samples), after cycling and after voltage hold (separate samples).

Mentions: The initial capacitance results at the different voltages are shown in Fig. 6a and the specific capacitance in SI Fig. S8. As with previous samples, the range of AC layer thicknesses results in a range of capacitances, but it is clear that for a given AC mass, the capacitance is considerably higher at 1.2 V. There is not a significant difference between the capacitances at 0.8 V and 1.0 V. The most probable reason for the increase at 1.2 V is pseudocapacitance, which is voltage-dependent. Because the AC ink was prepared in ambient air, as were the capacitors, a significant contributor to the pseudocapacitance is oxygen. It has been reported that pseudocapacitance is the reason for increasing capacitance with increasing voltage and it can account for up to 40% of measured device capacitance37. In this case, most pseudocapacitive reactions occur at a device voltage higher than 1.0 V.


Performance, stability and operation voltage optimization of screen-printed aqueous supercapacitors
(a) Initially measured capacitances of samples measured at different voltages, plotted against AC ink mass. Each data point is a different sample. (b) Change in capacitance after cycling and after voltage hold at different voltages; separate sample batches were used for the cycling and the hold. (c) Leakage current at different voltages initially (all samples), after cycling and after voltage hold (separate samples).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382703&req=5

f6: (a) Initially measured capacitances of samples measured at different voltages, plotted against AC ink mass. Each data point is a different sample. (b) Change in capacitance after cycling and after voltage hold at different voltages; separate sample batches were used for the cycling and the hold. (c) Leakage current at different voltages initially (all samples), after cycling and after voltage hold (separate samples).
Mentions: The initial capacitance results at the different voltages are shown in Fig. 6a and the specific capacitance in SI Fig. S8. As with previous samples, the range of AC layer thicknesses results in a range of capacitances, but it is clear that for a given AC mass, the capacitance is considerably higher at 1.2 V. There is not a significant difference between the capacitances at 0.8 V and 1.0 V. The most probable reason for the increase at 1.2 V is pseudocapacitance, which is voltage-dependent. Because the AC ink was prepared in ambient air, as were the capacitors, a significant contributor to the pseudocapacitance is oxygen. It has been reported that pseudocapacitance is the reason for increasing capacitance with increasing voltage and it can account for up to 40% of measured device capacitance37. In this case, most pseudocapacitive reactions occur at a device voltage higher than 1.0 V.

View Article: PubMed Central - PubMed

ABSTRACT

Harvesting micropower energy from the ambient environment requires an intermediate energy storage, for which printed aqueous supercapacitors are well suited due to their low cost and environmental friendliness. In this work, a systematic study of a large set of devices is used to investigate the effect of process variability and operating voltage on the performance and stability of screen printed aqueous supercapacitors. The current collectors and active layers are printed with graphite and activated carbon inks, respectively, and aqueous NaCl used as the electrolyte. The devices are characterized through galvanostatic discharge measurements for quantitative determination of capacitance and equivalent series resistance (ESR), as well as impedance spectroscopy for a detailed study of the factors contributing to ESR. The capacitances are 200–360 mF and the ESRs 7.9–12.7 Ω, depending on the layer thicknesses. The ESR is found to be dominated by the resistance of the graphite current collectors and is compatible with applications in low-power distributed electronics. The effects of different operating voltages on the capacitance, leakage and aging rate of the supercapacitors are tested, and 1.0 V found to be the optimal choice for using the devices in energy harvesting applications.

No MeSH data available.


Related in: MedlinePlus