Self‐Encapsulation of High‐Entropy Alloy Nanoparticles inside Carbonized Wood for Highly Durable Electrocatalysis

High‐entropy alloy nanoparticles (HEAs) show great potential in emerging electrocatalysis due to their combination and optimization of multiple elements. However, synthesized HEAs often exhibit a weak interface with the conductive substrate, hindering their applications in long‐term catalysis and energy conversion. Herein, a highly active and durable electrocatalyst composed of quinary HEAs (PtNiCoFeCu) encapsulated inside the activated carbonized wood (ACW) is reported. The self‐encapsulation of HEAs is achieved during Joule heating synthesis (2060 K, 2 s) where HEAs naturally nucleate at the defect sites. In the meantime, HEAs catalyze the deposition of mobile carbon atoms to form a protective few‐layer carbon shell during the rapid quenching process, thus remarkably strengthening the interface stability between HEAs and ACW. As a result, the HEAs@ACW shows not only favorable activity with an overpotential of 7 mV at 10 mA cm−2 for hydrogen evolution but also negligible attenuation during a 500 h stability test, which is superior to most reported electrocatalysts. The design of self‐encapsulated HEAs inside ACW provides a critical strategy to enhance both activity and stability, which is also applicable to many other energy conversion technologies. A defect‐driven surface engineering strategy is proposed to prepare a highly active and long‐lasting electrocatalyst composed of quinary high‐entropy alloy nanoparticles (HEAs) (PtNiCoFeCu) encapsulated inside the activated carbonized wood (ACW) through thermal shock. The surface defects of ACW exhibit thermodynamically stable adsorption on the melting HEAs, rendering HEAs to aggregate and nucleate at the defect sites of ACW.