Confined Atom Escape and Nucleation Delivering Iridium‐Based Nanoparticles with Ultrahigh Mass Activity for Acidic Water Oxidation

Abstract Achieving high catalytic activity and stability with as little iridium (Ir) as possible is essential for the widespread deployment of proton exchange membrane water electrolysis (PEMWE). Although single‐atom dispersion strategies could maximize the utilization of iridium, they usually suffer from unsatisfactory stability issues. Here, a method is reported of growing highly dispersed iridium‐based nanoparticles with unprecedented mass activity and stability through confined atom escape and nucleation (CAEN). Unlike conventional synthesis methods in which all metal precursors are free to nucleate, CAEN is characterized by a tunable confinement of metal single atoms in the carbon substrate by asymmetric nitrogen, oxygen‐coordination, which establishes a thermodynamic and kinetic equilibrium between single‐atom dispersion and nucleation, prevents the growth of metastable phases, and delivers highly stable nanoparticles with durable active surfaces. The acidic oxygen evolution reaction (OER) mass activity of the designed catalyst reaches 2040.8 A g Ir −1 , which is about 25 times that of commercial Ir/C (81.60 A g Ir −1 ), and the durability is improved by an order of magnitude. This CAEN method can be further extended to the synthesis of iridium‐based intermetallic nanoparticles, resulting in a more than 50‐fold increase in OER mass activity, opening up a completely new path for the design of high‐performance catalysts.