Electrochemical Intercalation of Oxygen in Nd2NiO4+x (0 .ltoreq. x .ltoreq. 0.18) at 298 K

Abstract

Electrochemical intercalation of oxygen into Nd{sub 2}NiO{sub 4+x} has been investigated by potential step experiments (5 mV steps, 10 {mu}A cutoff current) in aqueous 1 M KOH at 298 K. Stoichiometric Nd{sub 2}NiO{sub 4} is obtained on the initial reduction of the starting material Nd{sub 2}NiO{sub 4.18}. On reoxidation, a maximum composition of Nd{sub 2}NiO{sub 4.1} is obtained below the potential where oxygen evolution is observed. In the composition range 0.0 {le} x {le} 0.08 intercalation is reversible. The electrochemical data show two-phase behavior in the composition range 0.01 {le} x {le} 0.04 and a single-phase region 0.04 {le} x {le} 0.08. Parallel X-ray diffraction studies show that Nd{sub 2}NiO{sub 4+x} is orthorhombic for 0 {le} x {le} 0.01, tetragonal for 0.04 {le} x {le} 0.08 and orthorhombic at Nd{sub 2}NiO{sub 4.18}. An enthalpy of oxidation of -204 kJ/mol of O{sub 2} was obtained from the electrochemical data in the single-phase region. 37 refs., 6 figs., 1 tab.