Abstract
The reduction of hydrogen peroxide at the D.M.E. is catalyzed in lanthanum, salt solutions. In. 0.01 M La(NO 3) 3 it has been shown that a cathodic hydrogen peroxide current appears at +0.2 V vs. S.C.E., followed by a depression in the current which extends to the main hydrogen peroxide wave at −0.3 V. Experiments on suspensions of lanthanum hydroxide in lanthanum nitrate-hydrogen peroxide solutions have shown that the reduction current at potentials more oxidizing than −0.3 V increased upon contact with the solid, while the height of the normal wave decreased. Filtration of these mixtures and tests with potassium permanganate and nitric acid on the filtrate indicated that the species responsible for the reduction current was soluble, oxidizable, and unstable to acid. Mercury in contact with the lanthanum nitratehydrogen peroxide test solution led to the more rapid production of this species along with the evolution of oxygen. A soluble complex between lanthanum ion and hydrogen peroxide, formed under mildly alkaline conditions, is postulated as the species being reduced. The suppression of the catalytic current in the potential range +0.1 to −0–2 V is interpreted as the result of adsorption of insoluble lanthanum hydroxide or polymeric lanthanum hydroxy-complexes on the D.M.E. Current-time curves consistent with this explanation have been obtained.
Published Version
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