Highly efficient and durable anode catalyst layer constructed with deformable hollow IrOx nanospheres in low‐iridium PEM water electrolyzer

Reducing iridium packing density (gIr cm−3 electrode) represents a critical pathway to lower geometric Ir loading in proton exchange membrane water electrolyzers (PEMWEs), yet conventional approaches often cause performance issues of anode catalyst layer due to decreased structural stability and limited electron/mass transport efficiency. Here we present deformable hollow IrOx nanospheres (dh‐IrOx) as a structural‐engineered catalyst architecture that achieves an ultralow Ir packing density (20% of conventional IrO2 electrodes) while maintaining high catalytic activity and durability at reduced Ir loadings. Scalable synthesis of dh‐IrOx via a hard‐template method—featuring precise SiO2 nanosphere templating and conformal Ir(OH)3 coating—enables batch production of tens of grams. Through cavity dimension and shell thickness optimization, dh‐IrOx demonstrates excellent mechanical resilience to necessary electrode fabrication stresses, including high‐shear agitation (10,000 rpm), ultrasonic processing (> 20 kHz), and hot‐pressing (130 °C, 10 MPa). In anode catalyst layer the quasi‐ordered close packing of dh‐IrOx nanospheres simultaneously maximizes electrochemically active surface area, suppresses particle migration and agglomeration, and establishes percolated electron highways and rapid mass transport channels. The architectured anode delivers high PEMWE performance, while demonstrating excellent operational durability with <1.5% voltage loss over 3,000 hours, surpassing the stability of IrO2 nanoparticle‐based systems by a factor of at least 20.