Understanding the mechanisms and design principles for oxygen evolution and oxygen reduction activity on perovskite catalysts for alkaline zinc–air batteries

Abstract

The high cost and limited availability of the precious metal catalysts required for catalysing the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in metal–air batteries restrict the marketing of these clean energy technologies. Understanding the OER and ORR mechanisms and identifying a catalyst design principle that connects the properties of materials with catalytic activity can speed up the search for highly active and abundant metal-oxide catalysts to replace costly platinum. In this report, the OER and ORR mechanisms involving a redox cycle of LaNi_1−xFe_xO₃ perovskite-oxide catalysts for the zinc–air battery (ZAB) in alkaline media are presented. Here, we demonstrate that the electrocatalytic activity toward OER/ORR of LaNi_1−xFe_xO₃ catalysts is primarily correlated with their reduction rate (log υ_red,25), such as the shape of a volcano. In addition, the OER/ORR activities of rapidly oxidized catalysts (LaNi_1−xFe_xO₃, where x = 0.5, 0.7, 0.9) and rapidly reduced catalysts (LaNi_1−xFe_xO₃, where x = 0, 0.1, 0.3) are linearly associated with their reduction rates and oxidation rates, respectively. The Tafel plot and temperature-programmed reduction (TPR) analyses suggest that the activation of OH, a charge transfer from the catalyst, is a rate-determining step, which implies that the rapidly oxidized catalyst and rapidly reduced catalyst control the rate of OER and ORR redox cycles, respectively. Furthermore, the LaNi_0.5Fe_0.5O₃ catalyst appearing high on the volcano-shaped plot exhibits high OER/ORR activities, and thus highlights the importance of the electronic structure in controlling the perovskite-oxide catalytic activity.