Suppose, I am performing Cyclic voltammetry. With the change in potential, I will get different values of current. Why we need to convert the current into current density? And how to convert current to current density?
It is always a good practice to convert current into current density J (mA/cm2 for electrochemical measurments). In the electrochemical measurements, if you use same active material embedded on two conducting substrates of the same kind, having different geometrical surface areas, then you will get higher current for the substrate having higher surface area. That is why you should divide the measured current with the substrate surface area to make the result independent of the substrate surface area.
Agreed With Ayan, If you will not provide density how can you compare, some one can perform reaction at 10 cm2 and some will perform 1 cm2.
Dear Tapas,
The most straightforward answer is: for the sake of comparison. Only current densities are meaningful when comparing between electrodes with differing surface areas.
To convert to current density, the easiest way is to divide your current by the surface area of your electrode. This will give what is commonly called the 'geometric current density'. In areas like catalysis, where the performance of the electrode material really matters, getting the 'true current density' is usually a lot more difficult. This is because the actual surface of your electrode might be quite rough and therefore a lot higher than the geometrical surface area.
Good explanations are given above.
Nevertheless, as an area normalized property, current density is a valid term for those macro-electrodes, but it becomes less meaningful when the electrode size drops to below mm or sub-mm when the edge effect increases or the spherical diffusion contributes comparably to or more than the planar diffusion to the total measured current.
I would also like to point out there are some publications on battery or supercapacitor that claim confusingly mass normalized current as current density with a unit of A/g or mA/g. The correct term for mass normalized current is specific current. Current load is also more appropriate than current density to be associated with the unit of A/g or mA/g
Basically, a dimension (length, area and volume) normalized property is called property density, such as current density and energy density, whilst a quantity (mass and mole) normalized property is called specific property such as specific capacity and specific energy.
Note that when the amount of mass is normalised against volume, the concept of concentration is also widely used, particularly by chemists.
A detailed explanations were already given above
When you calculate a capacitance in experiment you should refer that capacitance to a particular active mass. In other words, you will not get same capacitance values if you load a different masses. In order to measure the capacitance (i.e from CDs) you will consider current densities which is current divided by mass (Id = I/m).
Normalising your quantities with respect to weight and volume [Gravimetric (quantity/kg) and volumetric (quantity / cm3) , respectively] is a good way to compare the performance of various products.
Thesis Discrete linear constrained multivariate optimization for po...
In order to compare geometric area specific responses for the current and resistances, and negate substrate surface area.
Hi Tapas,
Current is not an intrinsic property of the WE material, because, further the electrode material, it also depends on the surface area of the electrode. So, to ovoid this problem and to characterize the activity of the electrode material it is necessary to use current density = current/exposed surface area of the electrode. The latter depends only on the electrode material, and thus characterizes the activity of the WE.
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