Polymer electrolyte membrane fuel cells can generate high power densities with low local emissions of pollutants. Optimal ionomer-Pt/C catalyst interactions in the electrodes enable the efficient generation and transport of ions and electrons required for high fuel cell performances. Critical durability issues involve agglomeration of the Pt/C nanoparticles (Pt/C NPs) and ionomer during discharging. Our novel approach involves ionomer cross-linking immobilization for the fabrication of durable catalyst layers for application in alkaline anion exchange membrane fuel cells (AEMFCs). Pt/C NP catalysts are employed alongside a poly(2,6-dimethyl-p-phenylene oxide)-(PPO)-based quaternary ammonium ionomer (containing terminal styrenic side-chain groups) to form porous catalyst layers. Following thermally initiated cross-linking of the terminal vinyl groups, an interconnected ionomer network forms conductive shells around the Pt/C aggregates. Ex situ catalytic activity and in situ durability tests demonstrate that this immobilization strategy inhibits Pt/C NP coalescence without sacrificing catalyst layer porosity. An initial demonstration of an H2/O2 AEMFC containing the new CBQPPO@Pt/C cathode shows that high peak power densities can be achieved (1.02 W cm–2 at 70 °C, raising to 1.37 W cm–2 with additional 0.1 MPa back-pressurization).