Ultrasonic spray synthesis of strontium-doped palladium nanocatalysts for enhanced ORR activity in PEM fuel cells

In this study, the electrochemical performance of palladium (Pd)-based catalysts synthesized via the Ultrasonic Spray (US) method, with and without strontium (Sr) doping, was investigated for application in Proton Exchange Membrane Fuel Cells (PEMFCs). Structural analyses demonstrated that undoped US-Pd/C contained crystalline and uniformly dispersed Pd nanoparticles, while 1 wt.% Sr doping reduced crystallite size and introduced structural distortions that enhanced defect sites and electronic interactions. In contrast, 3 wt.% Sr led to particle agglomeration, porosity loss, and decreased accessibility of active sites, as confirmed by SEM, TEM, and EDX analyses. Electrochemical measurements revealed that the US-PdSr/C catalyst with 1 wt.% Sr exhibited a lower Tafel slope (0.24 V/dec), higher mass activity (1838 mA/mg), reduced ohmic resistance (~ 0.0029 Ωcm²), and superior power density (59.4 mW/cm²) compared to conventionally synthesized Pd/C. Polarization curves demonstrated notable improvements in both activation and ohmic regions, while a lower overpotential (0.51 V) indicated enhanced energy conversion efficiency. These findings confirm that the Sr-doped Pd catalyst synthesized via the US method delivers significantly improved electrochemical activity and efficiency over conventional Pd/C catalysts, positioning it as a promising candidate for high-performance and sustainable PEMFC applications.