Studies on the Catalytic Properties of Palladium–Niobium Electrocatalysts Supported on Carbon Nano-onions toward Isopropanol and Ethanol Electro-oxidation in an Alkaline Medium

Renewable energy systems have gained remarkable attention as potential green energy sources with escalating energy demand and environmental issues. Direct alcohol fuel cells are potential energy sources with quick start-up, zero emissions, and high power density. However, current electrocatalysts’ poor efficiency and catalytic activity hinder their commercialization. In this study, Pd–Nb metal nanoparticles (MNPs) supported on carbon nano-onions (CNOs) were synthesized using the polyol method for the electro-oxidation of isopropanol and ethanol in an alkaline medium. An inexpensive CNO support was synthesized using the soot-based approach. High-resolution transmission electron microscopy analysis confirmed the successful synthesis of CNOs with a quasi-spherical structure and concentric rings resembling an onion. The Fourier transform infrared spectroscopy analysis confirmed the presence of oxygen moieties on the surface of the CNOs, which were used to anchor the MNPs to the surface of the support. The X-ray photoelectron spectroscopy analysis confirmed the composition of the electrocatalysts and the presence of Pd and Nb in different oxidation states. The synthesized Pd–Nb/CNOs exhibited high catalytic activity and stability for isopropyl alcohol and ethanol electro-oxidation. The addition of Nb to Pd reduced the loading of Pd, thus reducing the cost of the electrocatalyst and improving the physicochemical properties and electrocatalytic activity of Pd toward isopropanol and ethanol electro-oxidation. The increased electrocatalytic activity of Pd–Nb/CNOs is attributed to the increased active sites on the surface of the MNPs and the synergistic effects arising from the CNO support and the Pd–Nb MNPs.