A Monolayer High‐Entropy Layered Hydroxide Frame for Efficient Oxygen Evolution Reaction

High-entropy materials with tailored geometric and elemental compositions provide a guideline for designing advanced electrocatalysts. Layered double hydroxides (LDHs) are the most efficient oxygen evolution reaction (OER) catalyst. However, due to the huge difference in ionic solubility product, an extremely strong alkali environment is necessary to prepare high-entropy layered hydroxides (HELHs), which results in an uncontrollable structure, poor stability, and scarce active sites. Here, a universal synthesis of monolayer HELH frame in a mild environment is presented, regardless of the solubility product limit. Mild reaction conditions allow this study to precisely control the fine structure and elemental composition of the final product. Consequently, the surface area of the HELHs is up to 380.5 m² g^-1. The current density of 100 mA cm^-2 is achieved in 1 m KOH at an overpotential of 259 mV, and, after 1000 h operation at the current density of 20 mA cm^-2, the catalytic performance shows no obvious deterioration. The high-entropy engineering and fine nanostructure control open opportunities to solve the problems of low intrinsic activity, very few active sites, instability, and low conductance during OER for LDH catalysts.