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Local Current density

Posted 2016年10月27日 GMT+8 14:51 4 Replies

Yasir Ali
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Hi every one
I have started modelling lithium ion battery in Comsol. I am confused abut the current densities used in porous electrode model. Can any one tell me the difference in local current density, exchange current density and iv current. Also which current i am finding from Buttler Volmer equation
Thanks
4 Replies Last Post 2016年12月3日 GMT+8 17:43
Lasse Murtomäki
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Posted: 9 years ago 2016年10月28日 GMT+8 14:13
Hi

Have you read carefully the pdf document coming along the tutorial?

Exchange current density is the inherent rate of an electrochemical reaction:

i0 = n·F·k0·(cO)^a·(cR)^(1-a), 0 < a < 1 (charge transfer coefficient)

Butler-Volmer gives you the local current density, but the measured current is an integral value over the whole electroactive area. That is the disadvantage of electrochemistry, i.e. current is not selective.

BR
Lasse
Hi Have you read carefully the pdf document coming along the tutorial? Exchange current density is the inherent rate of an electrochemical reaction: i0 = n·F·k0·(cO)^a·(cR)^(1-a), 0 < a < 1 (charge transfer coefficient) Butler-Volmer gives you the local current density, but the measured current is an integral value over the whole electroactive area. That is the disadvantage of electrochemistry, i.e. current is not selective. BR Lasse
Yasir Ali
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Posted: 9 years ago 2016年11月2日 GMT+8 11:35
Sir Thank you for your reply.
But Sir I am confused of whether the local current density and exchange current density is on the particle surface of electrode or on the overall electrode?
Sir Thank you for your reply. But Sir I am confused of whether the local current density and exchange current density is on the particle surface of electrode or on the overall electrode?
Lasse Murtomäki
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Posted: 9 years ago 2016年11月2日 GMT+8 15:21

Sir Thank you for your reply.
But Sir I am confused of whether the local current density and exchange current density is on the particle surface of electrode or on the overall electrode?


Exchange current is not a directly measurable quantity. As I explained it is the measure of the rate of the electrode reaction. Although current were zero, i.e. the two terms in Butler-Volmer equation cancel each other out, there is exchange current. All electrochemical reactions take place on the surface.

Local current density is local, it can vary along the surface and it can be different at different parts of the electrolyte solution. This is known as the primary current distribution. Only with very specific experimental arrangements you can possibly measure the current distribution on the electrode surface. For example, grain boundaries are electrochemically more active than plateaus. A catalyst particle on the surface has a higher current density that its surroundings. That is why modeling is useful.
[QUOTE] Sir Thank you for your reply. But Sir I am confused of whether the local current density and exchange current density is on the particle surface of electrode or on the overall electrode? [/QUOTE] Exchange current is not a directly measurable quantity. As I explained it is the measure of the rate of the electrode reaction. Although current were zero, i.e. the two terms in Butler-Volmer equation cancel each other out, there is exchange current. All electrochemical reactions take place on the surface. Local current density is local, it can vary along the surface and it can be different at different parts of the electrolyte solution. This is known as the primary current distribution. Only with very specific experimental arrangements you can possibly measure the current distribution on the electrode surface. For example, grain boundaries are electrochemically more active than plateaus. A catalyst particle on the surface has a higher current density that its surroundings. That is why modeling is useful.
Yasir Ali
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Posted: 9 years ago 2016年12月3日 GMT+8 17:43
Thank You Sir for your reply
Thank You Sir for your reply

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