Thermodynamic Analysis of Size-Dependent Surface Energy in Pd Nanoparticles for Enhanced Alkaline Ethanol Electro-Oxidation

This work investigates the relationship between the mean diameter of palladium (Pd) nanoparticles and their surface energy, specifically in the context of alkaline ethanol electro-oxidation for fuel cell applications. Employing a recent generalization of the classical Laviron equation, we derive crucial parameters such as surface energy (<i>σ</i>), adsorption-desorption equilibrium constant (<i>K_eq</i>), and electron transfer coefficient (<i>α</i>) from linear voltammograms obtained from Pd-based nanoparticles supported on Vulcan carbon. Synthesized using two distinct methods, these nanocatalysts exhibit mean diameters ranging from 10 to 41 nm. Our results indicate that the surface energy of the Pd/C nanocatalysts spans <i>σ</i> ~ 0.5-2.5 J/m², showing a linear correlation with particle size while remaining independent of ethanol bulk concentration. The adsorption-desorption equilibrium constant varies with nanoparticle size (~0.1-6 × 10^-6 mol^-1) but is unaffected by ethanol concentration. Significantly, we identify an optimal mean diameter of approximately 28 nm for enhanced electrocatalytic activity, revealing critical size-dependent effects on catalytic efficiency. This research contributes to the ongoing development of cost-effective and durable fuel cell components by optimizing nanoparticle characteristics, thus advancing the performance of Pd-based catalysts in practical applications. Our findings are essential for the continued evolution of nanomaterials in fuel cell technologies, particularly in improving efficiency and reducing reliance on critical raw materials.