The Cr(III) complexes present in the acidified chromium solutions used in the iron-chromium redox energy storage system have been isolated and identified as Cr(H20)6 ~ and Cr(H20)sC1 § by ion-exchange chromatography and visible spectrophotometry. The cell reactions during charge-discharge cycles have been followed by means of visible spectrophotometry. The spectral bands were resolved into component peaks and concentrations of the Cr(III) species calculated using Beer's law. During the charge mode, Cr(H~O)sCt +2 is reduced to Cr(H20)sCF, and during the discharge mode Cr(H20)~C1 § is oxidized back to Cr(H~O)sC1 § Electrode potential measurements also support this interpretation. Hysteresis effects in the charge-discharge curves can be explained by the slow attainment of equilibrium between Cr(H20)~ +3 and Cr(H20)~C1 §

Cyclic voltammetric, coulometric, and chronocoulometric data associated with the reduction of Rh(en)2Cl~ + at mercury electrodes are reported that confirm previous results indicating the occurrence of a two-electron reduction to produce the hydrido complex, Rh (en)2H (OH2)2+ which engages in a pH dependent equilibrium involving Rh(en)2+: Rh(en)2H(OH2) ~+ + OH-Rh(en)~ + + 2H20. The resulting presence of Rh(en)2 + at the electrode surface has a number of interesting consequences which are described. Among these are the electrochemical production of metal-metal bonded rhodiummercury adducts, apparent strong adsorption of Rh(en)~ + on the electrode surface, and anomalous cyclic voltammograms with inverted peaks.

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Die Reduktion der Titelverbindung an Hg‐Elektroden wird durch cyclische Voltammetrie, Coulometrie und Chronocoulometrie untersucht.