Highly Active Pd-CeO2-NR/C (cerium oxide nanorods) Bifunctional Nanocatalysts with Remarkable Stability for the Ethanol Oxidation and Oxygen Reduction Reactions in Alkaline Media

Monday, 14 October 2019
Grand Ballroom (The Hilton Atlanta)
P. C. Meléndez-González (Cinvestav Unidad Saltillo), M. E. Sánchez-Castro (CINVESTAV UNIDAD SALTILLO), I. L. Alonso-Lemus (CONACYT. Cinvestav Saltillo), R. Pérez-Hernández (ININ), M. T. Ochoa-Lara (CIMAV), B. Escobar-Morales (Centro de Investigación Científica de Yucatán), P. Quintana-Owen (Cinvestav Unidad Mérida), A. M. Garay-Tapia (Cimav Monterrey), and F. J. Rodríguez-Varela (Cinvestav Unidad Saltillo)
The electrochemical stability and catalytic activity of 20 wt. % Pd-CeO2-NR/C (Pd:CeO2-NR 1:1 atomic ratio) and 20 wt. % Pd/C nanocatalysts for the Oxygen Reduction Reaction (ORR) and the Ethanol Oxidation Reaction (EOR) in 0.5 mol L-1 KOH is evaluated in this work. The nanocatalysts have been synthesized by the polyol method. The morphology and chemical composition of the synthesized Pd-CeO2-NR/C and Pd/C have been determined in a Field Emission Scanning Electron Microscope (FESEM) with an energy dispersive X-Ray detector. The results show a chemical composition close to the nominally expected. Meanwhile, the XRD analysis demonstrates the crystalline nature of the nanocatalysts with crystallite size of Pd-CeO2-NR/C and Pd/C of 11.8 and 7.9 nm, respectively. XPS analysis indicates mainly the presence of Pd0, Pd2+, and Pd4+ species on both electrocatalyst, as well as Ce3+ and Ce4+ in Pd-CeO2-NR/C. It has been determined that after accelerated degradation test (ADT, 3000 cycles between 0.6 and 1.0 V/RHE), the ECSA loss of Pd-CeO2-NR/C is of around 3 %, clearly smaller compared to 80 % in the case of Pd/C, which suggests a synergic effect between CeO2-NR and Pd that stabilizes the metallic nanoparticles. Evaluation by RRDE shows that Pd-CeO2-NR/C has a catalytic activity for the ORR similar to Pd/C in terms of onset potential of the ORR (0.98 and 0.94 V/RHE before ADT, respectively; 0.91 and 0.92 V/RHE after ADT, respectively). Nevertheless, Pd-CeO2-NR/C delivers higher mass and specific activities than Pd/C, with both nanocatalysts producing about the same amount of H2O2 (around 3 - 4.5 %). Meanwhile, the polarization curves of the EOR before ADT show a peak mass current density of 697.70 mA mgPd-1 generated by Pd-CeO2-NR/C (at 0.86 V/RHE), higher than 665.66 mA mgPd-1 obtained from Pd/C (at 0.92 V/RHE). After ADT, the mass current density increased by 1.6 and 1.4 times at Pd-CeO2-NR/C and Pd/C, respectively. The results show that Pd-CeO2-NR/C is a highly electrochemically stable bifunctional nanocatalysts with high catalytic activity for the ORR and the EOR in alkaline media, which make it a promising candidate for A-DEFCs applications.