Type III supercapacitor

FIGURE 9.10 Cyclic voltammogram of a Type III supercapacitor prepared from PDTT in 0.2 M TEABF4 in propylene carbonate at 50 mV/s. The dotted line is the electrical response of bare carbon paper electrodes. (Adapted from Arbizzani, C. et at, Electrochim. Acta, 40, 1871, 1995. With permission Copyright 1995, from Elsevier.)... 

Loveday et al. [170] proposed the use of self-n-doping polymers in Type III supercapacitors. Self-n-doping was expected to alleviate cation transport problems and enhance the n-doping process, thus enhancing device performance. While the polymer, poly-3-(p-trimethylammoniumphenyl)hithiophene (Figure 9.4N) showed promising n-doping, no supercapacitor device properties were reported. 

Figure 9 shows the discharge curves of a Type I polypyrrole-based, a Type II polypyrrole/poly(3-methylthiophene)-based and a Type III poly(dithieno[3,4-6 3, 4 -d]thiophene-based supercapacitor at 4 mA cm discharge current. Types I and II can be assembled using such conventional heterocyclic polymers as polypyrrole, polyaniline and polythiophene, which are efficiently p-dopable polymers and can easily be chemically or electrochemically synthesized from inexpensive... 

Structural formulas of some PT derivatives are shown in Figure 28.3. PT can be both n-doped and p-doped. As follows from Table 28.3, anodic capacitance (under p-doping) of PT derivatives is higher than its cathodic capacitance (under n-doping). Therefore, the cathode in PsCs of type III must be thicker than the anode. It was found that conductivity in the n-doped form is lower than in the p-doped form conductivity in the n-doped form is rather low. Most of PT derivatives are stable in air and in a moist state both in the p-doped and undoped forms. Symmetrical type HI supercapacitors with PT derivatives on both electrodes were manufactured. Herewith, the energy density of 30-40 Wh/kg and power density of 5-10 kW/kg per mass of active materials was reached. Table 28.3 shows the characteristics of PsCs based on poly-3-(3,4-difluorophenyl)thiophene (PDFPT) and poly-3-(4-cyanophenyl)thiophene (PCPT). One can see that rather high energy density values were obtained in this case (Table 28.5). 

In Type III and Type IV supercapadtors, ox(anode)- red(cathode) typically ranges from 0.8 to 3 V [ 147]. The overvoltage is approximately the same as that of a Type I supercapacitor (perhaps less due to the sensitivity of n-doped polymers), meaning that Type in and Type IV supercapacitors typically have... 

FIGURE 9.9 Comparison of voltage decay characteristics for Type I, Type n, and Type III and IV supercapacitors. 

Several other polymers have also been evaluated for use in Type I supercapacitors. While polythiophene exhibits an excellent specific capacitance for energy storage (250 F/g) [160], polythiophene supercapacitors are uncommon, possibly due to cycle life issues. However, derivatives of polythiophene have been used in the preparation of Type II, Type III, and Type IV supercapacitors (see Section 9.3.6.2 and Section 9.3.6.3). 

Charge Transport in NiO NiO is one of the few metal oxides that are p-type in nature and is also studied for applications such as smart windows and supercapacitors. As prepared, the nanostructured material has some surface colouration attributed to Ni(III) sites on the smface. At negative potentials, or in the presence of a mild chemical reducing agent, the material can be bleached. On scanning to positive potentials the colour turns brown then black. The spectroelectrochemistry was studied by Boschloo and Hagfeldt, and two surface redox reactions were observed (Figure 3.70) attributed to oxidation of Ni to Ni coupled... 

---