You can use EIS to determine the exchange current density. If you get a copy of J. Ross MacDonald's "Impedance Spectroscopy: Emphasizing Solid Materials and Systems" the equations are in there. Pretty much, you need to find the interfacial reaction resistance (Theta) and then it is just:
theta = RT/nFI_0
I_0 = exchange current density
F = Faraday's constant
n = number of electrons exchanged at the interface
The exchange current density determines a good Nernstian sensor, see attachment.
What different with exchange current ? how to measure exchange current ? in the fuel cell system
I agree with the answer of Jayasree vjx from University of Kerala in that the exchange current density is the current density at open circuit potential. Thus the exchange current density for hydrogen evolution at the surface of Pt is the highest among all other metals. In this case the exchange current density give us idea about activity and Pt surface is the best choice as an electrode for hydrogen evolution.
You can plot the tafel fit and find the exchange current density at an overpotential=0
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