Ternary PdNiO nanocrystals-ornamented porous CeO₂/onion-like carbon for electrooxidation of carbon monoxide: unveiling the effect of supports and electrolytes

Porous ternary Pd-based catalysts are highly promising for various electrocatalytic applications, due to their low Pd mass, high surface area, accessible active sites, and tunable electronic structure; however, their activity for CO oxidation (CO_oxid) in different electrolytes is yet to be reported. Herein, ternary PdNiO nanocrystals supported on porous CeO₂/onion-like carbon nanostructures (PdNiO-CeO₂/OLC) were prepared by the sol-gel and impregnation approaches for electrochemical CO_oxid in different electrolytes at room temperature. Notably, porous CeO₂/OLC acts as a support and nanoreactor for supporting the growth of PdNiO without the need for reducing agents or surfactants. The as-obtained PdNiO-CeO₂/OLC had a porous sponge-like structure composed of ultra-small PdNiO nanocrystals (8 ± 1 nm) distributed on porous flower-like CeO₂ and OLC, which possessed unique merits of multifunctional structure, clean surface, low mass of Pd (10 wt%), porosity (0.30 cm³ g⁻¹), and high surface area (155.66 m² g⁻¹). The CO_oxid activity of PdNiO-CeO₂/OLC was higher than those of PdNiO/OLC, PdNiO-CeO₂, and commercial Pd/C catalyst, owing to the electronic interaction of PdNiO with CeO₂/OLC support, which eases CO adsorption/activation alongside activation/dissociation of H₂O to generate active oxygenated species (i.e., OH) needed for accelerating CO_oxid kinetics. The CO_oxid activity of PdNiO-CeO₂/OLC in acidic electrolyte (HClO₄) was better than those in alkaline (KOH) and neutral (NaHCO₃) electrolytes. This study may open new doorways for understanding the effect of electrolytes and supports on the CO_oxid activity of porous ternary Pd-based catalysts.