Ultrathin two-dimensional medium-entropy oxide as a highly efficient and stable electrocatalyst for oxygen evolution reaction

Medium-entropy oxides (MEOs) with broad compositional tunability and entropy-driven structural stability, are receiving booming attention as a promising candidate for oxygen evolution reaction (OER) electrocatalysts. Meanwhile, ultrathin two-dimensional (2D) nanostructure offers extremely large specific surface area and is therefore considered to be an ideal catalyst structure. However, it remains a grant challenge to synthesize ultrathin 2D MEOs due to distinct nucleation and growth kinetics of constituent multimetallic elements in 2D anisotropic systems. In this work, an ultrathin 2D MEO (MnFeCoNi)O was successfully synthesized by a facile and low-temperature ionic layer epitaxy method. Benefiting from multi-metal synergistic effects within ultrathin 2D nanostructure, this 2D MEO (MnFeCoNi)O revealed excellent OER electrocatalytic performance with a quite low overpotential of 117 mV at 10 mA·cm⁻² and an impressive stability for 120 h continuous operation with only 6.9% decay. Especially, the extremely high mass activity (5584.3 A·g⁻¹) was three orders of magnitude higher than benchmark RuO₂ (3.4 A·g⁻¹) at the same overpotential of 117 mV. This work opens up a new avenue for developing highly efficient and stable electrocatalysts by creating 2D nanostructured MEOs.