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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) Nyquist plots of selected samples from approximately 0.2 Hz to the high frequency range. (b) Characteristic time plotted against capacitance with galvanostatically measured ESR as colour scale (colour online). (c) Capacitance versus AC ink mass and (d) leakage current against capacitance for 1 M KCl and NaNO3 samples, compared to NaCl samples (open symbols).
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f4: (a) Nyquist plots of selected samples from approximately 0.2 Hz to the high frequency range. (b) Characteristic time plotted against capacitance with galvanostatically measured ESR as colour scale (colour online). (c) Capacitance versus AC ink mass and (d) leakage current against capacitance for 1 M KCl and NaNO3 samples, compared to NaCl samples (open symbols).

Mentions: Nyquist plots of selected samples are shown in Fig. 4a. At low frequencies (below approximately 1 Hz) the curves are nearly vertical, characteristic to ideal capacitance. At higher frequencies, a 45° line is observed, corresponding to capacitance and resistance distributed in a porous material [2, p. 389]. From approximately 200–400 Hz to 200–600 kHz an RC loop is found. The shape of the loop is not a perfect semicircle and the centre is below the real axis, which can be caused by distributed elements in the system as well as simultaneous processes with slightly different time constants30. The size of the loop stays the same when the device is measured in the charged state, at 0.9 V (not shown). From this we infer that Faradaic processes (pseudocapacitance) are not responsible for the semicircle, as the associated resistance should be voltage-dependent2. The loop is most likely due to an imperfect contact interface between the current collector and the active layer: Portet et al. have shown that an interface capacitance and resistance form a parallel RC element in series with the supercapacitive one, giving rise to a semicircle31.


Performance, stability and operation voltage optimization of screen-printed aqueous supercapacitors
(a) Nyquist plots of selected samples from approximately 0.2 Hz to the high frequency range. (b) Characteristic time plotted against capacitance with galvanostatically measured ESR as colour scale (colour online). (c) Capacitance versus AC ink mass and (d) leakage current against capacitance for 1 M KCl and NaNO3 samples, compared to NaCl samples (open symbols).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: (a) Nyquist plots of selected samples from approximately 0.2 Hz to the high frequency range. (b) Characteristic time plotted against capacitance with galvanostatically measured ESR as colour scale (colour online). (c) Capacitance versus AC ink mass and (d) leakage current against capacitance for 1 M KCl and NaNO3 samples, compared to NaCl samples (open symbols).
Mentions: Nyquist plots of selected samples are shown in Fig. 4a. At low frequencies (below approximately 1 Hz) the curves are nearly vertical, characteristic to ideal capacitance. At higher frequencies, a 45° line is observed, corresponding to capacitance and resistance distributed in a porous material [2, p. 389]. From approximately 200–400 Hz to 200–600 kHz an RC loop is found. The shape of the loop is not a perfect semicircle and the centre is below the real axis, which can be caused by distributed elements in the system as well as simultaneous processes with slightly different time constants30. The size of the loop stays the same when the device is measured in the charged state, at 0.9 V (not shown). From this we infer that Faradaic processes (pseudocapacitance) are not responsible for the semicircle, as the associated resistance should be voltage-dependent2. The loop is most likely due to an imperfect contact interface between the current collector and the active layer: Portet et al. have shown that an interface capacitance and resistance form a parallel RC element in series with the supercapacitive one, giving rise to a semicircle31.

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