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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.

No MeSH data available.


Effect of unequal electrode capacitances on maximum charging voltage.Cyclic voltammograms of (a) chemically synthesised PPY-CNT (20 wt%) in two different potential windows, and (b) asymmetrical supercapacitors of (blue line) “5 mg PPY-CNT (+) / KCl / 10 mg AC (−)” at C+/C− = 1.0, and (red line) “24 mg PPY-CNT (+) / KCl / 11 mg AC (−)” at C+/C− = 3.0. Specific capacitance: 180 F g−1 for PPY−CNT and 125 F g−1 for activated carbon. Electrolyte: 3 mol L−1 KCl. Scan rate: 5 mV s−1.
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f6: Effect of unequal electrode capacitances on maximum charging voltage.Cyclic voltammograms of (a) chemically synthesised PPY-CNT (20 wt%) in two different potential windows, and (b) asymmetrical supercapacitors of (blue line) “5 mg PPY-CNT (+) / KCl / 10 mg AC (−)” at C+/C− = 1.0, and (red line) “24 mg PPY-CNT (+) / KCl / 11 mg AC (−)” at C+/C− = 3.0. Specific capacitance: 180 F g−1 for PPY−CNT and 125 F g−1 for activated carbon. Electrolyte: 3 mol L−1 KCl. Scan rate: 5 mV s−1.

Mentions: To further investigate the capacitance unequalisation strategy, a single cell supercapacitor of “PPY-CNT (+) / KCl / AC (−)” was fabricated and studied. In this cell, the AC was a commercial activated carbon (Kuraray, specific surface area: 1500~1800 m2 g−1). Its specific capacitance was measured to be 125 F g−1 in the potential range of −0.9 ~ 0.2 V vs Ag/AgCl in 3 mol L−1 KCl. The PPY-CNT used was chemically synthesised as described before6 with the CNT content being controlled to be 20 wt.%. The CVs of this chemically synthesised PPY-CNT are presented in Fig. 6a, exhibiting features, particularly the CPR, almost identical to those of the electro-deposited PPY-CNT (Fig. 2).


Cell voltage versus electrode potential range in aqueous supercapacitors
Effect of unequal electrode capacitances on maximum charging voltage.Cyclic voltammograms of (a) chemically synthesised PPY-CNT (20 wt%) in two different potential windows, and (b) asymmetrical supercapacitors of (blue line) “5 mg PPY-CNT (+) / KCl / 10 mg AC (−)” at C+/C− = 1.0, and (red line) “24 mg PPY-CNT (+) / KCl / 11 mg AC (−)” at C+/C− = 3.0. Specific capacitance: 180 F g−1 for PPY−CNT and 125 F g−1 for activated carbon. Electrolyte: 3 mol L−1 KCl. Scan rate: 5 mV s−1.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Effect of unequal electrode capacitances on maximum charging voltage.Cyclic voltammograms of (a) chemically synthesised PPY-CNT (20 wt%) in two different potential windows, and (b) asymmetrical supercapacitors of (blue line) “5 mg PPY-CNT (+) / KCl / 10 mg AC (−)” at C+/C− = 1.0, and (red line) “24 mg PPY-CNT (+) / KCl / 11 mg AC (−)” at C+/C− = 3.0. Specific capacitance: 180 F g−1 for PPY−CNT and 125 F g−1 for activated carbon. Electrolyte: 3 mol L−1 KCl. Scan rate: 5 mV s−1.
Mentions: To further investigate the capacitance unequalisation strategy, a single cell supercapacitor of “PPY-CNT (+) / KCl / AC (−)” was fabricated and studied. In this cell, the AC was a commercial activated carbon (Kuraray, specific surface area: 1500~1800 m2 g−1). Its specific capacitance was measured to be 125 F g−1 in the potential range of −0.9 ~ 0.2 V vs Ag/AgCl in 3 mol L−1 KCl. The PPY-CNT used was chemically synthesised as described before6 with the CNT content being controlled to be 20 wt.%. The CVs of this chemically synthesised PPY-CNT are presented in Fig. 6a, exhibiting features, particularly the CPR, almost identical to those of the electro-deposited PPY-CNT (Fig. 2).

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.