The electrochemical properties of lithiated nickel oxide in the form of mosaic crystals have been examined. Linear sweep voltarnmetry of this oxide in HISOd, HCl, HCIOI, and NaOH reveals a reversible peak at @9 V(he), which corresponds closely in potential to that assigned by Pourbaix to the Ni(II)/Ni(III) oxide couple. In HISOl a second peak is evident at 1.4 V which corresponds closely to the potential for the Ni(III)/Ni(IV) couple. Dissolution rates have been studied in HCl at elevated temperatures and found to be surprisingly small. A step-like increment in dissolution rate occurs at potentials corresponding to the first peak (0.9 V) in the voltamrnetry curves.
Various redox couples have been examined on the lithiated NiO crystals. In all instances, the cathodic process is inhibited relative to the anodic process. Tafel linearity has been found for the oxidation of ferrous and ferrocyanide ions after correction for mass-transport control, but the Tafel slopes vary from electrode to electrode at constant lithium content and tend to be lower at low rotation rates. Oxygen reduction to the peroxide is also substantially inhibited as compared with the reverse process. The relative inhibition of cathodic processes is as would be expected generally for a p-type semiconductor.
R&rm&Examen
des proprietes 6lectrochimiques de l'oxyde de nickel lithme, sous forme de mosaIque cristalline. Un balayage voltametrique lin6aire de cet oxyde darts H&50,, HCl, HClO,, NaOH, revele un pit reversible a 0,9 V (e.h.), ce qui correspond exactement au potentiel attribud par Pourbaix au couple d'oxydes Ni(II)/Ni(III).
Dans HpSOl un second pit est manifeste a I,4 V, ce qui correspond exactement au potentiel du couple Ni(III)/Ni(IV).
Les vitesses de dissolution darts HCl a temperatures &levees se rt%lent Btonnamment faibles. Un accroissementdiscontinu de la vitesse de dissolution se produit cependant a des potentiels correspondant au premier pit (0,9 V) des courbes voltametriques.
Analyse des divers couples redox propres aux cristaux de NiO lithine. Darts tous les cas, le processus cathodique est inhibb par rapport au processus anodique. La dependance lineaire de Tafel a 6te observee dans l'oxydation des ions ferreux et ferrocyanure, apr&s correction du contr&le par transport de masse, mais les pentes de Tafel se moditient dune electrode a une autre electrode, de m&me teneur en lithium et tendent a dirninuer aux faibles vitesses de rotation. La reduction de l'oxygene en peroxyde est egalement inhib&e notablement, par rapport au processus inverse. L'inhibition relative des processus cathodiques est analogue a celle que l'on pourrait generalement pr&oir avec un semi-conducteur de type p.