Diffusion towards solid film in an electrochemical system was studied from nonequilibrium thermodynamic point of view. To this aim, electrochemical redox of Prussian blue in the presence of different supporting electrolyte cations was chosen as a well-known system. The variation of the phenomenological coefficient was investigated. The theory derived from theoretical hypothesis was supported by experimental results obtained from chronoamperimetric and cyclic voltammetric measurements. The fulfillment of reciprocity Onsager relation was also presented. Interestingly, it was demonstrated that the phenomenological coefficient for a diffusing electrochemical system is strongly time-dependent, and can be considered as a dynamic representative of the flux. (C) 2003 Elsevier Science B.V. All rights reserved.