Ultrasonic spray fabrication of palladium–chromium Nanocatalysts for high performance oxygen reduction in proton exchange membrane fuel cells

Developing cathode catalysts is crucial for the widespread use of proton exchange membrane (PEM) fuel cells. An ultrasonic spray (US) method was employed as an energy-efficient alternative for synthesizing chromium (Cr) and palladium–chromium (Pd[sbnd]Cr) nanocatalysts. This technique utilizes an ultrasonic atomizer to generate a liquid–vapor interface reaction, resulting in the formation of USCr-Pd and US-CrPd nanocatalysts supported on Vulcan XC-72R carbon. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and inductively coupled plasma optical emission spectrometry (ICP-OES) analyses were performed to characterize the structural, morphological, elemental, and compositional properties of the synthesized nanocatalysts. Structural characterization by X-ray diffraction (XRD) revealed crystallite sizes of 1.53 nm for USCr-Pd/C and 0.79 nm for US-CrPd/C, indicating the successful synthesis of highly dispersed and nanoscale alloyed catalysts. Cyclic voltammetry (CV) measurements showed electrochemically active surface area (ECSA) values of 9.1 m²/g_Pd and 11.3 m²/g_Pd for USCr-Pd/C and US-CrPd/C, respectively. Voltage-current density curves show that fuel cell activity increases with temperature. Using the ultrasonic spray method, the catalysts achieved maximum power densities of 147 mW/cm² for USCr-Pd/C and 164 mW/cm² for US-CrPd/C at 70 °C. In contrast, without ultrasonic spray, the performance remained significantly lower at 28 mW/cm² for Pd/C and 73 mW/cm² for PdCr/C. This study highlights the potential of the US method for producing high-performance nanocatalysts, offering a scalable and energy-efficient alternative for PEM fuel cell applications.