Textile electrodes electrolytes

Scheme of the electrochemical cell described in section 9.2.2, consisting of (1) PVC plates, (2) rubber-ring fittings, (3) PVC tube, (4) electrolyte solution, (5) screws to tighten the cell parts and avoid leaking of electrolyte solution and (6) palladium sheet or textile electrodes. 

Similar to the experiments carried out at palladium electrodes and described in Chapter3, the concentration of electrolyte (c), the electrode surface area (A) and the distance between the electrodes (d) will be studied as a function of type of textile structure. In this work, three structures will be studied knitted, woven and non-woven textile structures, all obtained from stainless-steel fibres. To complete the data of this work, palladium sheets will also be inserted in the study as a fourth set of electrodes. Therefore, for palladium electrodes, the work described in section 9.2 will actually be repeated here in order to have a direct comparison between results obtained with palladium electrodes and textile electrodes. Of course, correlation with the data obtained in section 9.2 will be verified. 

Finally, it can be seen from Fig. 9.9a that the real impedance does not remain constant at low frequencies for the textile electrode, and this effect is more pronounced at higher electrolyte concentrations. Probably, Zr is influenced by other effects only occurring in the low-frequency range. This effect is frequently observed and described in the literature and is caused by non-uniformity of surfaces at the micro-scale, which in fact is the case for the textile electrodes. It is also not possible to explain this effect by a pure resistor or a pure capacitor in the electrical equivalent circuit. For this purpose, constant-phase elements are implemented as described in the theoretical discussion of electrochemical impedance spectroscopy (presented in Chapter 2, section 2.4). 

Scheme showing the positioning of a palladium electrode (a) and a woven (b) and knitted (c) textile electrode in the cell, and the influence on the configuration of the electrodes due to positioning. (1) Rubber fittings, (2) part of the PVC tubing filled with electrolyte and (3) electrolyte solution. 

In this section, the distance between the electrodes is studied for different electrolyte concentrations and distances between the electrodes at a constant electrode surface area of A = 180 mm2. The obtained impedances are plotted logarithmically against the distance between the electrodes (d) as shown in Fig. 9.14. Relationships obtained for the textile electrodes are identical to those for the palladium electrodes if the smallest distance between the electrodes is not taken into account. Additionally in this case, the roughness of the textile electrodes is responsible for this effect and can be neglected for distances longer than d=40mm - an effect that increases with decreasing distance between the electrodes. Of course, also in this case,... 

Logarithmic plot of the impedance at zero phase-angle shift as a function of distance between the electrode (d) obtained from the electrochemical cell with palladium and textile electrodes, A= 490.6mm2, 7 =298.0K and an electrolyte concentration of (1)... 

In this section, the behaviour of the textile electrodes when used for a longer period in the electrochemical cell is investigated. It is expected that this behaviour can change as a function of time because of uptake of electrolyte solution by the textile electrodes and possible corrosion reactions that can occur. Additionally in this case, the data and results obtained for the textile electrodes will be compared with those obtained for palladium electrodes. Bode and Nyquist plots are recorded for the four types of electrodes and the electrolyte resistance was measured as a function of time for electrolyte concentrations of 1 xlCT1,1 xlO 2,1 xlO 3 and 1 xl(T4moll The values for A and d are 180 mm2 and 103 mm, respectively. For all these concentrations, the resistances are summarised in Tables9.9-9.12. 

A possible explanation for this effect can be found in the 3D structure of textile electrodes and its permeability for liquids. While slowly soaking electrolyte solution, the contact surface between textile electrode and electrolyte increases. The latter effect gives rise to a decrease in the resistance because of a larger value for A. As this process is occurring reasonably... 

Long-term stability tests of (1) palladium sheet electrodes and (2) woven, (3) knitted and (4) non-woven textile electrodes, obtained by measurement of R as a function of time in the electrochemical cell for NaCI electrolyte concentrations of (a) 1x10 4, (b) 1x10 3, (c) 1 x10 2 and (d) 1 x10 1 mol I-1. 

The availability of an inert electrolyte is of the utmost importance for the development of a quality-control system for textile electrodes. In such a system, it is the aim to test the quality of textile electrodes therefore the condition and properties of the electrode should not be changed or influenced during this quality-control experiment. This condition cannot be fulfilled by using NaCl as electrolyte solution, because during the quality testing, the chloride will affect the properties of the textile electrode tested. 

Most recently Beaupre et al. developed a flexible electrochromic device using textile in 2006 [71]. The structure is made with a transparent electrode, covered with spray-coated electrochromic polymer, a gel electrolyte and finally with a conductive textile. The textile electrode is made with a textile fabric coated with copper and nickel. The other electrode is made of glass or polyester (PET) coated with ITO. Two electrochromic conductive polymers have been tested. Similar colours and colour changes are obtained for structures using two PET-ITO electrodes, or two glass-ITO electrodes, or one textile electrode with one PET-ITO electrode. The colour change is visible but slow. When a plastic electrode and a textile electrode are used, the structure is flexible. A similar structure, using a copper-coated textile cathode, was described by Zhan et al. in 2013 [72]. 

Hu et al. [2] produced a lithium ion textile battery in which they wove a conductive porous 3D stracture from conductive yams made of pure polyester dispersed with carbon nanotubes. These porous stmctures are then filled with battery electrode material and electrolyte. The assembly is then stuck on a flat metallic piece that is the current collector. 

These supercapacitors use modified conventional textile material as the base material and then thin active layers of electrodes and electrolyte are applied on it. The textile fabric can also be used as the main active components of the supercapacitor, say the electrode or the separator or the holder of the active elements. If the textile material is used as the base, it is normally modified by adding conductive polymers or metal particles to it by various techniques (coating, printing, deposition, dispersion, or on-site polymerization of conductive polymer). 

In Other scenario for a simple capacitor, the textile substrate can be used as a separator or dielectric material or carrier of electrolyte. The electrodes are then applied on both sides of the textiles. 

Textile-based energy storage devices were fabricated with PEDOTiPSS as the electrolyte, conductive yams as yam electrodes, and textile substrate. Copper-coated PBO filament yams, silver-coated PBO filament yarns, and pure stainless steel filament yams were used as yam electrodes to produce different types of devices. These charge storage devices were well integrated into textile stmcture, making them lightweight and flexible. The devices could be easily fabricated. 

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