The water fuel electrochemical cell capacitor

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I want to discuss about the behavior of the double layer differential capacitance, and other features of this electrochemical devices.

There are two currents that can flow in an electrochemical device, one is a faradaic current, and the other is a capacitive current.

Macroscopically when you insert two electrodes into a dielectric liquid you get a macroscopic capacitor.

When you consider the electrode electrolyte or dielectric interface other things start to appear.

When a metal is inserted in water its called an electrode. Electrodes has their own polarity according to its ability to hold electrons at its lattice, for example platinum is very nonreactive while sodium dangerously ionizes..

When iron for example is inserted in water, a collection of oxygen negative ions will be attracted to its surface leaving at the surface the bare iron atoms positive charges, while inside the iron there is free negative charge. 

As the positive ions get desorbed into the solution more negative charge gets into the iron up to a point where desorption ceases.

Another capacitance than shows up in the sense that for each charge in the metal there will be an equal and opposite charge separated by a distance at the surface of the electrode in the "dielectric".

This distance depends on the force of the electric field thereto is a non linear capacitance, that increases with applied voltage potential since the distance between the ions must reduce.

This capacitance is dependent on the ion density, temperature, voltage, materials...

http://books.google.com.br/books?id=2g5GJtBFwo0C&pg=PA22&lpg=PA22&dq=electrochemical+cell+capacitance&source=bl&ots=0Pvf3D_qJY&sig=t5R80by9ynHyrimXmBGKK5Bjymg&hl=pt-BR#v=onepage&q=electrochemical%20cell%20capacitance&f=false

http://uqu.edu.sa/files2/tiny_mce/plugins/filemanager/files/27/08_Appendix.pdf

http://www.fq.uh.cu/dpto/qf/docencia/pregrado/dinamica_1/bibliografia/electroch_cells.pdf

http://geogratis.cgdi.gc.ca/eodata/download/part6/ess_pubs/225/225015/cr_2008_05.pdf

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According to the last resource... Stainless steel has around 40uF for each square cm. for a solution of 0.01N NaCl ...

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Great resources!

Br,
Webmug

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I don't know what if this is the capacitance used for resonance... as it in series with the water volume capacitance its contribution should be very low so much that is not considered many times...

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Capacitance is usually defined as the stored charge between two conducting surfaces separated by a dielectric divided by the voltage between the surfaces.  Another definition is the rate of change of the stored charge or surface charge (σ) divided by the rate of change of the voltage between the surfaces or the electric surface potential (ψ).  The latter is called the "differential capacitance," but usually the stored charge is directly proportional to the voltage, making the capacitances given by the two definitions equal.

This type of differential capacitance may be called "parallel plate capacitance," after the usual form of the capacitor.  However, the term is meaningful when applied to any two conducting bodies such as spheres, and not necessarily ones of the same size, for example, the elevated terminals of a Tesla wireless system and the earth.  These are widely spaced insulated conducting bodies positioned over a spherically conducting ground plane.[3]

    "The differential capacitance between the spheres is obtained by assuming opposite charges ±q on them. . . ." [4]

Another form of differential capacitance refers to single isolated conducting bodies. It is usually discussed in books under the topic of "electrostatics."  This capacitance is best defined as the rate of change of charge stored in the body divided by the rate of change of the potential of the body.  The definition of the absolute potential of the body depends on what is selected as a reference.  This is sometimes referred to as the "self-capacitance" of a body.  If the body is a conducting sphere, the self-capacitance is proportional to its radius, and is roughly 1pF per centimetre of radius.

The WFC has a TUBE and ROD as exciter plates so there must be "differential capacitance". It has two unequal double layers.

Regards

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Webmug i guess this name its more related to the fact that this capacitance is a function of voltage and it follows a differential equation... not sure...