Highly Stable Twin Defects Enabled by High Entropy Configuration.

The strategic engineering of crystalline defects has been proven effective in enhancing the efficiency of metallic catalysts. However, owing to the confined and metastable nature of these defects, controlling their formation in nanosized particles remains challenging, especially in multi-element alloy catalysts, where complex interactions further complicate defect stabilization. Herein, we report concentrated and stable twin defects in carbon-confined FeCoNiMn nanocatalysts (denoted as T-FeCoNiMn/C), spotlighting entropy-sensitive formation mechanisms and durable catalytic performance. By integrating deep learning, in situ transmission electron microscopy (TEM) and molecular dynamics simulations, we reveal the atomic-scale strain distribution in T-FeCoNiMn/C and disclose the multi-step formation dynamics of these twin defects. Notably, the entropy-enhanced multielement nature endows twin defects with highly flexible atomic configurations and a broad energy landscape, allowing structurally adaptable high-energy configurations to relax into more energetically favorable twins rather than detwinning; ultimately, highly concentrated and stable twin configurations prevail throughout not only the synthesis process but also the following catalysis service for oxygen evolution reactions. Our findings demonstrate entropy-driven twin defect stabilization in metallic nanocatalysts, offering new strategies for catalytic structural engineering.