高负载铂（Pt）阴极催化层是实现重载型质子交换膜燃料电池（PEMFCs）高性能运行的关键，但其长期面临离聚物磺酸基团毒化与Pt纳米颗粒稳定性难以兼顾的矛盾。本文提出一种空间限域策略，通过将高含量Pt纳米颗粒（约51.8 wt%）封装于锰-氮-碳（Mn-N-C）纳米笼中，构筑了具有离聚物屏蔽微环境的Pt-MnNC催化剂。该介孔笼状结构可有效阻隔离聚物进入其内部，显著降低了磺酸基团对Pt活性位点的吸附毒化；同时，Mn–N_x位点与Pt之间的强金属-载体相互作用能够稳定锚定Pt纳米颗粒，抑制其迁移与团聚。在5 × 5 cm²膜电极测试中，Pt-MnNC催化剂在2.0 A·cm^-2电流密度下实现1.26 W·cm^-2的峰值功率密度。经过30000次加速耐久性测试后，其质量活性仅下降20.8%，显著优于商业Pt/C催化剂（衰减61.6%）。研究结果表明，空间限域构筑的离聚物屏蔽微环境能够有效缓解离聚物磺酸基团对Pt的毒化，并协同增强Pt纳米颗粒稳定性，为高功率密度、长寿命重载型PEMFC阴极催化剂的设计提供了新的思路。

High-loading Pt cathodes are essential for heavy-duty proton exchange membrane fuel cells (PEMFCs) but suffer from a critical trade-off between ionomer sulfonate poisoning and nanoparticle instability. Herein, we report a spatial confinement strategy to encapsulate dense Pt nanoparticles (~51.8 wt%) within Mn/N-co-doped mesoporous carbon nanocages (denoted as Pt-MnNC). This architecture excludes bulky ionomers to create an ionomer-shielded environment against sulfonate poisoning, while Mn-N_x-mediated strong metal-support interactions anchor the Pt nanoparticles to prevent agglomeration and further boost durability. In 5×5 cm² membrane electrode assembly (MEA) tests, the Pt-MnNC catalyst delivers an exceptional peak power density of 1.26 W·cm^-2 at 2.0 A·cm^-2. Notably, it exhibits superior durability with only a 20.8% mass activity loss after 30,000 cycles, significantly outperforming commercial Pt/C, which suffers a 61.6% loss. This work provides a robust pathway to decouple ionomer poisoning from catalyst loading, advancing the development of high-power, durable heavy-duty fuel cells.