High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) offer improved tolerance to fuel impurities, simplified water management, and enhanced reaction kinetics relative to low-temperature systems. Despite these advantages, their large-scale deployment is still limited by the high platinum loadings required at both electrodes: the anode, to sustain efficient hydrogen oxidation (HOR) under elevated temperatures, and especially the cathode, where oxygen reduction reaction (ORR) kinetics dominate performance losses and cost. Reducing Pt content at both electrodes without compromising activity or durability remains a critical challenge. This work presents a scalable approach to the fabrication of electrocatalysts based on electrodeposited core-shell nanoparticles, enabling a drastic reduction in Pt loading and achieving notable HT-PEMFC performance.

Catalyst nanoparticles were electrodeposited directly onto the microporous layer (MPL), which already contains conductive carbon-based supports, ensuring precise control over particle size, distribution, and metal content, and achieving ultra-low Pt loadings. Beyond catalyst synthesis, this study focuses on the critical role of ionomer content within the catalyst layer on membrane electrode assembly (MEA) performance. While ionomer is essential for proton transport and catalyst utilization, excessive or insufficient ionomer concentrations can severely hinder gas diffusion, electronic connectivity, and active site accessibility. Systematic optimization of ionomer concentration revealed a narrow operating window in which electrodeposited nanoparticle catalysts exhibit maximal performance. At optimized ionomer loadings, improved triple-phase boundary formation and reduced mass transport losses were observed, resulting in enhanced cell voltage and power density.

The combined strategy of electrodeposition-based catalyst fabrication and ionomer optimization demonstrates a viable pathway toward high-performance HT-PEMFCs with drastically reduced Pt loadings. These findings underscore the importance of integrated catalyst-ionomer design in MEA engineering and provide valuable insights for the development of next-generation, low-cost fuel cell technologies.