Strongly‐Anchored Ionomer‐Free Anode Catalyst Layer Fabricated via Joule Heating Achieves Efficient Electron/Mass Transfer for Acidic Water Electrolysis

ABSTRACT Conventional ionomer‐based membrane electrode assemblies (MEAs) in proton exchange membrane water electrolysis (PEMWE) suffer from severe catalyst agglomeration and high interfacial resistance, especially at ultralow iridium loadings. These issues, stemming from the insulating nature and uneven distribution of ionomers, significantly restrict electron and mass transport. Herein, we present a novel ionomer‐free anode catalyst layer (ACL) fabricated via a rapid Joule heating method, which partially anchors IrO ₂ nanoparticles into the proton exchange membrane (PEM) to form an ultrathin (~0.7 μm), dense, and crack‐free ACL, forming a robust mechanical anchoring interface. The resulting MEA with ionomer‐free ACL structure (MEA‐J) effectively mitigates ionomer‐induced catalyst agglomeration and adhesion failure, achieving 99.7% catalyst electronic connectivity, a fivefold increase in volumetric active area, and over tenfold stronger interfacial adhesion compared to conventional MEA. Lattice Boltzmann simulations further verify that the continuous and conformal water films formed in the ionomer‐free ACL serve as efficient pathways for proton/water transport, comparable to hydrated bulk ionomers. The MEA‐J achieves a current density of 3.1 A·cm ⁻² at 2.0 V with an ultralow Ir loading of 0.2 mg _Ir ·cm ⁻² , and exhibits exceptional durability, sustaining stable operation for over 2200 h at 1 A·cm ⁻² with an ultralow voltage degradation rate of 5.1 μV·h ⁻¹ . This work establishes the ionomer‐free ACL as a transformative pathway for the development of high‐performance and durable PEMWE.