Influence of CeO₂ Nanoparticle Morphology on the Electrocatalytic Activity of Palladium toward the Formate...

This study investigates the electrocatalytic activity of palladium (Pd) nanocatalysts combined with nanoparticles (NPs) of cerium oxide (CeO₂) polyhedra (Pd/CeO₂/C poly) and with morphologies of cube (Pd/CeO₂/C NC), hexagonal sheet (Pd/CeO₂/C NS), and nanorod (Pd/CeO₂/C NR) for the formate electrooxidation reaction (FER) in an alkaline medium, a key process in direct formate fuel cells (DFFCs). X-ray diffraction (XRD) patterns indicate that the CeO₂ NP dislocation density follows the decreasing order of Pd/CeO₂/C NR > Pd/CeO₂/C NS > Pd/CeO₂/C NC > Pd/CeO₂/C poly. This order corresponds to the Pd⁰ concentration observed in X-ray photoelectron spectroscopy (XPS) data. Pd/CeO₂/C NR showed CeO₂ NPs with compressive microstrain values, while the other materials presented tensile microstrain. Pd/CeO₂/C NR showed a higher amount of oxygen vacancies in XPS analysis. Transmission electron microscopy (TEM) micrographs showed Pd NPs surrounding and in close contact with CeO₂ NPs. The average Pd NPS size was 4-10 nm, while CeO₂ NC, CeO₂ NS, and CeO₂ poly showed 30, 15, and 50 nm, respectively. The length and width of CeO₂ NR were 100 and 10 nm, respectively. Cyclic voltammetry (CV) demonstrates that Pd/CeO₂/C NR exhibits higher catalytic activity toward FER than the other materials studied (Pd/C, Pd/CeO₂/C NC, Pd/CeO₂/C NS, Pd/CeO₂/C poly). Chronoamperometric analysis (CA) shows that the current density from FER on Pd/CeO₂/C NR at the end of the experiment was 2.65 times higher than on Pd/C, while for Pd/CeO₂/C NC and Pd/CeO₂/C NS it was 1.45 and 1.13 times higher than on Pd/C. The enhanced catalytic activity of Pd/CeO₂/C NR results from the interaction between palladium and ceria, involving microstrain, oxygen vacancies, and metal-support interaction, facilitating polar adsorbate adsorption. This makes Pd/CeO₂/C NR a promising catalyst for direct formate fuel cell applications.