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Cell voltage versus electrode potential range in aqueous supercapacitors

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ABSTRACT

Supercapacitors with aqueous electrolytes and nanostructured composite electrodes are attractive because of their high charging-discharging speed, long cycle life, low environmental impact and wide commercial affordability. However, the energy capacity of aqueous supercapacitors is limited by the electrochemical window of water. In this paper, a recently reported engineering strategy is further developed and demonstrated to correlate the maximum charging voltage of a supercapacitor with the capacitive potential ranges and the capacitance ratio of the two electrodes. Beyond the maximum charging voltage, a supercapacitor may still operate, but at the expense of a reduced cycle life. In addition, it is shown that the supercapacitor performance is strongly affected by the initial and zero charge potentials of the electrodes. Further, the differences are highlighted and elaborated between freshly prepared, aged under open circuit conditions, and cycled electrodes of composites of conducting polymers and carbon nanotubes. The first voltammetric charging-discharging cycle has an electrode conditioning effect to change the electrodes from their initial potentials to the potential of zero voltage, and reduce the irreversibility.

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Voltages of asymmetrical supercapacitors.Cyclic voltammograms of asymmetrical supercapacitors of (a) 900 mC PAN-CNT (+) / 1.0 mol L−1 HCl / 2 mg CMPB (−), (b) 630 mC PPY-CNT (+) / 0.5 mol L−1 KCl / 1 mg CMPB (−), and (c) 3 C PEDOT-CNT (+) / 0.5 mol L−1 KCl / 1.7 mg CMPB (−). Voltage scan rates: (a) 10, (b) 20 and (c) 10 mV s−1, respectively.
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f4: Voltages of asymmetrical supercapacitors.Cyclic voltammograms of asymmetrical supercapacitors of (a) 900 mC PAN-CNT (+) / 1.0 mol L−1 HCl / 2 mg CMPB (−), (b) 630 mC PPY-CNT (+) / 0.5 mol L−1 KCl / 1 mg CMPB (−), and (c) 3 C PEDOT-CNT (+) / 0.5 mol L−1 KCl / 1.7 mg CMPB (−). Voltage scan rates: (a) 10, (b) 20 and (c) 10 mV s−1, respectively.

Mentions: As shown in Fig. 2, the CMPB is a good negative electrode to work together with a pseudocapacitive positive electrode. Thus, asymmetrical tube-cell supercapacitors were constructed with CMPB and conducting polymer-CNT composite as the negative and positive electrode materials respectively. Following the convention, the capacitances of the two electrodes were made equal. Typical results from testing such asymmetrical tube-cells are presented in Fig. 4, confirming the expected larger MCVs. For example, the asymmetrical supercapacitor of “PAN-CNT (+) / HCl / CMPB (−)” had an MCV of 1 V (Fig. 4a), notably higher than that of the PAN-CNT symmetrical capacitor which is about 0.65 V as shown in Fig. 3b.


Cell voltage versus electrode potential range in aqueous supercapacitors
Voltages of asymmetrical supercapacitors.Cyclic voltammograms of asymmetrical supercapacitors of (a) 900 mC PAN-CNT (+) / 1.0 mol L−1 HCl / 2 mg CMPB (−), (b) 630 mC PPY-CNT (+) / 0.5 mol L−1 KCl / 1 mg CMPB (−), and (c) 3 C PEDOT-CNT (+) / 0.5 mol L−1 KCl / 1.7 mg CMPB (−). Voltage scan rates: (a) 10, (b) 20 and (c) 10 mV s−1, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384324&req=5

f4: Voltages of asymmetrical supercapacitors.Cyclic voltammograms of asymmetrical supercapacitors of (a) 900 mC PAN-CNT (+) / 1.0 mol L−1 HCl / 2 mg CMPB (−), (b) 630 mC PPY-CNT (+) / 0.5 mol L−1 KCl / 1 mg CMPB (−), and (c) 3 C PEDOT-CNT (+) / 0.5 mol L−1 KCl / 1.7 mg CMPB (−). Voltage scan rates: (a) 10, (b) 20 and (c) 10 mV s−1, respectively.
Mentions: As shown in Fig. 2, the CMPB is a good negative electrode to work together with a pseudocapacitive positive electrode. Thus, asymmetrical tube-cell supercapacitors were constructed with CMPB and conducting polymer-CNT composite as the negative and positive electrode materials respectively. Following the convention, the capacitances of the two electrodes were made equal. Typical results from testing such asymmetrical tube-cells are presented in Fig. 4, confirming the expected larger MCVs. For example, the asymmetrical supercapacitor of “PAN-CNT (+) / HCl / CMPB (−)” had an MCV of 1 V (Fig. 4a), notably higher than that of the PAN-CNT symmetrical capacitor which is about 0.65 V as shown in Fig. 3b.

View Article: PubMed Central - PubMed

ABSTRACT

Supercapacitors with aqueous electrolytes and nanostructured composite electrodes are attractive because of their high charging-discharging speed, long cycle life, low environmental impact and wide commercial affordability. However, the energy capacity of aqueous supercapacitors is limited by the electrochemical window of water. In this paper, a recently reported engineering strategy is further developed and demonstrated to correlate the maximum charging voltage of a supercapacitor with the capacitive potential ranges and the capacitance ratio of the two electrodes. Beyond the maximum charging voltage, a supercapacitor may still operate, but at the expense of a reduced cycle life. In addition, it is shown that the supercapacitor performance is strongly affected by the initial and zero charge potentials of the electrodes. Further, the differences are highlighted and elaborated between freshly prepared, aged under open circuit conditions, and cycled electrodes of composites of conducting polymers and carbon nanotubes. The first voltammetric charging-discharging cycle has an electrode conditioning effect to change the electrodes from their initial potentials to the potential of zero voltage, and reduce the irreversibility.

No MeSH data available.