Ionic layer epitaxy synthesis of ultrathin two-dimensional high-entropy alloy electrocatalyst for highly efficient and stable oxygen evolution reaction

Abstract Confined to ultrathin two-dimensional (2D) architectures, high-entropy alloys (HEAs) could leverage synergistic cocktail effects and entropy-stabilized phases to enable exceptional oxygen evolution reaction (OER) kinetics and stability via maximized specific surface areas and quantum confinement. However, synthesizing atomically precise 2D HEAs remains fundamentally challenging due to disparate metal nucleation kinetics. Herein, we demonstrate a facile low-temperature (80 °C) ionic layer epitaxy synthesis of ultrathin 2D HEA FeCoNiMo. The OER catalytic activity exhibited a strong inverse correlation with the 2D HEA thickness, where atomic-scale dimensional reduction significantly enhanced electrocatalytic performance. Atomic-scale confinement to 1.1 nm thickness unlocks exceptional OER performance. This 1.1 nm 2D HEA FeCoNiMo revealed a record-low overpotential of 79 mV at 10 mA·cm–2 and unprecedented stability (