Niobium: a promising Pd co-electrocatalyst for ethanol electrooxidation reactions

Abstract

This work reports the sol–gel synthesis and characterization of Pd x Nb y /C binary electrocatalysts applied to ethanol electrooxidation reactions (EORs). Catalysts were prepared using different Pd/Nb mass ratios (1:0; 1:1; 1:3; 3:1; 0:1) and were supported on Vulcan XC-72 carbon (20 wt%). The materials were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. The EOR catalytic activity was studied by cyclic voltammetry (CV) and chronoamperometry (CA). The results showed that the EOR current density peak using Pd1Nb1/C (45.5 mA mg−1) was 2.86 times higher than that of commercial Pd/C (15.9 mA mg−1). This catalyst also showed a less positive EOR onset potential and 2.35 times higher current density than Pd/C did in CA. The Pd1Nb1/C (− 0.54 V) showed onset potential more negative than Pd/C (− 0.50 V) for CO-stripping analysis. Additionally, the addition of Nb in the Pd/C reduces COads poisoning of the electrocatalyst. The results suggest that Nb decreases the poisoning effect of CO on the Pd surface due to the bifunctional mechanism in which Nb supplies oxygenated species for CO oxidation at poisoned Pd active sites. No evidence of Pd/Nb alloy formation has been found. The maximization of the bifunctional effect occurs in Pd1Nb1/C.