Abstract
Electrocatalytic activity for the four-electron-transfer oxygen reduction reaction (ORR) was examined with perovskite-type La0.7Sr0.3Mn1–xNixO3—δ (x = 0–0.5) compounds in concentrated KOH. Electrochemical measurements by means of a rotating ring–disk electrode technique revealed that 10% substitution of Mn by Ni atoms significantly improved ORR activity whereas further Ni substitution significantly decreased the catalytic performance. Moreover, La0.7Sr0.3Mn0.9Ni0.1O3—δ could achieve the ideal reaction electron number (∼4) without the aid of carbon additives, whereas compounds with x > 0.1 achieved a number less than 4 in the absence of carbon cocatalysts, attributed to lowered reaction rates related to two-electron reduction from oxygen to peroxide. Combined with the results of X-ray photoelectron spectroscopy, the pronounced catalytic activity of La0.7Sr0.3Mn0.9Ni0.1O3—δ could be correlated with the population of Mn3+ states with (eg)1 configuration.
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