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Bifunctional electrocatalysis refers to the catalytic behavior of a single electrode material that promotes two distinct electrochemical reactions at different electrode potentials, most commonly the oxygen reduction reaction at the cathode and the oxygen evolution reaction at the anode in rechargeable metal-air batteries and unitized regenerative fuel cells ^[1]. A bifunctional oxygen catalyst must simultaneously exhibit high activity and low overpotential for both the four-electron reduction of oxygen to water and the reverse oxidation of water to oxygen, while remaining stable over the wide potential window that alternates between reducing and oxidizing conditions during discharge and charge cycles ^[2]. The activity of such materials is governed by the electronic structure of the catalytically active sites—particularly the occupancy of transition-metal d-orbitals, the covalency between metal and oxygen, and the adsorption energetics of reaction intermediates such as hydroxyl, oxide, and peroxide species on the surface ^[3]. Non-precious-metal candidates including manganese oxides, perovskite oxides, and transition-metal-nitrogen-carbon composites are evaluated by the potential gap between the oxygen evolution and reduction polarization curves.