3.14 Electrochemical Potential

• Usually in ionic systems, both the effects of gradients in chemical and electrical potential on the mobilities are present.

• Non-uniform distribution of charged defects can give rise to internal electric field even in the absence of external electric field.

• Total driving force for mass transport is defined as Electrochemical potential.

       The electrochemical potential of spices i , denoted as η_i, is the sum of the chemical  potential μ_i, and electric potential φ acting upon it and can be written as

	(3.55)

       where Z_i is the effective charge and F is Faraday's constant (=96500 Coulomb/mol).

       Now, virtual force on the particle is negative gradient of η_i i.e.

	(3.56)

       Flux, J, can be expressed as

	OR

	(3.57)

       This shows that flux, J_i , is a function of electric field, (dφ/dx).