Paolo Salvi

Electrochemical Activation of Raney Nickel Air Electrodes

We study slow and nearly reversible processes of reduction, hydride formation and oxidation in Raney-Ni air electrodes in concentrated KOH solutions. A labile ?-NiH phase is formed upon prolonged cathodic polarization under H2 atmosphere. Repeated cathodic/anodic cycles enhance hydrogen intake and induce surface modifications of the Raney-Ni grains.

Charge storage and the oxygen evolution reaction in mixed Ni–Li oxides

Electronic and catalytic properties of mixed oxides of Ni-Li are studied at room temperature with NMR and with electrochemical techniques in alkaline solutions. Our Li(x)Ni(1-x)O (0.04 < or = x < or = 0.2) samples have an f.c.c crystal structure, are in an anti-ferromagnetic phase, and exhibit a substantial conductivity due to a hole-hopping process with a characteristic rate which is essentially independent of composition. Several processes of reduction and oxidation occur in the voltage region between the hydrogen (HER) and oxygen evolution (OER) reactions, which are compared with related phenomena observed in pure Ni electrodes (Ni(OH)2 and NiO). Repeated cycles of reduction and oxidation yield electrodes with a somewhat improved OER activity, and a high charge-storage capacity. Heavy anodic treatments cause irreversible changes of these properties, particularly when coupled with months-long storage in air. The complex behavior of these electrodes is interpreted in terms of formation of a topotactic surface layer with hydrogenated species.

Ni - based Electrodes for Hydrogen and Oxygen Generation

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 daylong treatments greatly enhance the red ox reactions of the Nielectrodes which occur between hydrogen evolution (HER) and oxygen evolution reactions (OER). The effects upon HER and OER are also discussed.

The Apparent Capacitance of the Electrode "Charging" Process

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.

Reactions at a Porous Ni Electrode Concurrent with Hydrogen evolution

We summarize some of the difficulties we had in understanding the behavior of Ni electrodes, and Raney Ni in particular, in the hydrogen evolution reaction. We give a preliminary presentation of a set of experiments where the behavior of smooth or porous electrodes are compared after being conditioned with different protocols of polarization or of oxidation/reduction cycles.