Effect of the viscosity on the electrical response of a hydrosolution

Pirri

et al. 2012

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The effect of the dye-impregnation time on the electrical impedance of a dye-sensitized solar cell is theoretically investigated. The proposed model is based on the assumption that during the impregnation processes the covering of the titania electrodes, initially incomplete, arrives to saturation and the adsorption coverage can be described by a diffusive process, depending on the square root of the impregnation time. An equivalent circuit, formed by an electrical impedance related to the bulk contribution due to the electrolyte, and by a contribution due to the presence of the porous electrode partially covered by the dye is derived. The equivalent circuit is able to justify the experimental data recently reported on the influence of the dye-impregnation time on the electrical response of a solar cell. We show that a more complete analysis of the response of the solar cell to an external excitation, performed using the equations of continuity of the ions present in the electrolyte, and the equation of Poisson for the actual electric potential across the cell, allows to justify the proposed equivalent electric circuit.

Section: Resultssupporting

confidence: 84%

Influence of the dye impregnation time on the electrical impedance of a solar cell

Pirri

et al. 2012

Self Cite

“…procedure used in Ref. 12, in the present paper we measure the macroscopic viscosity and elastic, G 0 , and viscous, G", modulus versus the frequency, and the crossing frequency f c , where G 0 (f c ) ¼ G"(f c ) for two types of hydrogels doped with different concentration of NaCl. We measure also the frequency dependence of the real and imaginary parts of the electrical impedance of different samples, in the range 5 Hz, 13 MHz.…”

Section: -mentioning

confidence: 99%

“…This point is rather delicate because the dispersion of the viscosity takes place in the low frequency region (of the order of a few tens of Hz) and hence a possible frequency dependence of the diffusion coefficient could be responsible for unexpected frequency dependencies in the low part of the spectrum, usually attributed to surface effects, and modeled as constant phase elements. 10,11 In a recent paper 12 we have investigated the curves of voltammetry of a sample of hydrosolution. In Ref.…”

mentioning

confidence: 99%

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Influence of the rheological properties on the electrical impedance of hydrogels

Meyer

2012

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We show that the anomalous frequency dependence of the real part of the electrical impedance of hydrogels can be interpreted by taking into account their non-Newtonian character, according to which the effective viscosity, η, depends on the frequency of the imposed deformation. Our experimental results are in good agreement with the Poisson–Nernst–Planck model if the ionic viscosity is taken proportional to the macroscopic one, measured by means of a viscositymeter, and the diffusion coefficient is assumed frequency dependent according to the formula of Stokes D = KBT/(κη), where κ is a shape coefficient. From this result it follows that the non-Newtonian character of complex liquid can be investigated by means of the impedance spectroscopy technique.

“…25,26 Such dependence will have effects on the spectra of R(x) and X(x). 27,28 Here, we test the efficiency of this model to fit experimental data by investigating the electrical response of cells filled with hydrogel doped with different concentrations of KCl. The hydrogels are based on hydroxyethilcellulose (HEC) in deionized water, in which a small quantity of salt KCl is added.…”

Section: Introductionmentioning

confidence: 99%

Evidence for frequency dependent diffusion in hydrogel

Scalerandi

2014

Self Cite

The electrical response of a hydrogel to an external periodic voltage is investigated by means of the impedance spectroscopy technique. We show that the experimental data, obtained in the linear regime, for the real and imaginary parts of the electric impedance can be interpreted using the Poisson-Nernst-Planck model, taking into account the frequency dependence of viscosity and the non blocking character of the electrodes. We estimate the parameters (ion density, electrode conductivity, and diffusion coefficient) when varying the quantity of salt in the hydrogel. Our experimental data indicate that the bulk density of ions increases with the salt concentration, tending to a saturation value, whereas the electrode conductivity is independent of it. Finally, the parameters defining the dispersion of the diffusion coefficient depend weakly on the salt concentration.