Textile electrodes electrolyte concentration

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). 

Logarithmic plot of the impedance at zero phase-angle shift as a function of electrode surface area obtained from the electrochemical cell with palladium and textile structure electrodes, c/=103mm, 7"=298.0Kand an electrolyte concentration of (1) 10, (2) 10 2, (3) 10 3 and (4) 10 4moll. ... 

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,... 

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. 

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. 

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