Synergetic 3D Ni/Pd Air Cathodes for Optimizing Triple-Phase Boundaries Reaction and Catalytic Activity in Li-O₂ Batteries

Abstract

Li-O₂ batteries (LOBs) have attracted attention as promising next-generation energy storage devices for applications requiring high energy density due to their high theoretical energy density. The electrochemical performance of LOBs is determined by the reaction kinetics at the triple-phase boundary (TPB), where Li⁺, e⁻, and O₂ participate. However, conventional air cathodes face challenges such as sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), poor cycle life and reduced energy efficiency due to the limited TPB area, hindering their commercialization. To address these limitations, this study proposes a three-dimensional (3D) nanostructured Ni/Pd air cathode featuring highly ordered 3D Ni structures uniformly coated with Pd. Therein, 3D Ni forms a uniform TPB and serves as a current collector with excellent electrical conductivity and high mechanical strength. Additionally, Pd, uniformly deposited on the Ni surface, acts as a catalyst to enhance electrochemical reactions, while its spherical morphology increases surface roughness, thereby facilitating TPB expansion. The 3D Ni/Pd air cathode efficiently suppresses electrode oxidation achieving the synergistic effects of uniform TPB formation and the high catalytic activity of Pd. As a result, compared to the Ni foam/Pd air cathode with a limited TPB area, it exhibits a significant improvement in energy efficiency from 76.63% to 82.72% and cycle life from the 33rd to the 136th cycle. This design emphasizes the synergetic integration of an ordered 3D topology and Pd catalyst toward enhanced energy efficiency and chemical stability of LOBs.