Degradation mechanism of electrodes subjected to alternating potentials: modeling and protection

Abstract Non-symmetrical degradation of electrodes working in alkaline solutions and submitted to alternative potentials is analyzed from electrical conductance Σ analyses. Degradation rate of pure metal or composite electrodes is measured as a function of the working time t and of the period N of the applied potential. Logarithmic representations of the decrease of Σ ( t , T ) have been validated from elemental modeling. In a first approach, the degradation is describe using the Avrami model. Then, a three-steps semi-empirical model is proposed, that seems better adapted to our problem. The first step corresponds to the incubation of the corrosion, and the two other steps correspond to the growth of corrosion products, first on the surface of the electrode (2D corrosion), then in the bulk (3D corrosion). The lifetimes of the coatings are also connected with the frequency ν . A mechanism of protection is proposed.