Search

We investigate simple models of the electrode charging (discharging) at constant current i, where the potential (E) is recorded as a function of time, or charge, q = i ? t . Our goal is to assess the advantages of a representation in terms of capacitance,C = dq / dE ,vs. E. Such a plot is related with cyclic voltammetry (c.v.) plot (ic.v. vs E) at a constant rate (? = dE / dt)since, under appropriate circumstances, we should have C = ic.v. / ? = dq / dE . We will discuss the following items: a) origins and suppression of the singularities in the capacitance plots, b) effects of the finite charging currents, c) comparison between c.v. and electrode charging experiments.

We discuss the effects of treatments (cathodic/anodic conditioning, red ox cycles) upon the electrochemical properties of Ni-based electrodes in concentrated alkaline solutions. We find that day-long treatments greatly enhance the red ox reactions of the Ni-electrodes which occur between hydrogen evolution (HER) and oxygen evolution reactions (OER). The effects upon HER and OER are also discussed.

The electrochemical behaviour of Nickel in sulphuric acid electrolytes was studied by various electrochemical means. Under cathodic polarization, Nickel forms metastable hydrides under cathodic charging; the successive egress of hydrogen is controlled by solid state diffusion of hydrogen atoms. The nature of these hydrides evolves with electrochemical aging of the samples, as judged by their electrochemical signature. The nature of the (hydro)oxides formed during anodic polarization also evolves with aging. Anodic polarization and investigation of electrochemical oscillations in the transpassive region show that defect states which constitute preferred dissolution sites assume a wider energy range with increasing aging, indicating a high degree of inhomogeneity of the surface. The catalytic activity of Nickel increases after aging under both cathodic and anodic conditions, due to the formation of an inhomogeneous surface.