Investigation of Ni2+-doped ceria nanorods as the anode catalysts for reduced-temperature solid oxide fuel cells

Tailoring the surface chemistry of oxides has been widely used to adjust their catalytic behavior in the energy conversion and storage devices. Herein, nanorods of Ni2+-doped ceria (Ce1-xNixO2-delta, x = 0, 0.05, 0.1, 0.15) are synthesized via a modified hydrothermal method, and evaluated as the anode catalysts for reduced-temperature solid oxide fuel cells (SOFCs). X-Ray diffraction patterns of as-synthesized powders in air imply successful incorporation of Ni2+ into the fluorite lattice of ceria for x = 0.05 and 0.1, with a secondary phase of NiO observed for x = 0.15. Transmission electron microscopy (TEM) examination confirms a rod-like morphology with a diameter of 10-13 nm and a length of 55-105 nm. Exposure of these powders in H-2 at 600 degrees C results in exsolution of some spherical Ni particles of 11 nm in diameter. Electrochemical measurements on both symmetrical anode fuel cells and functioning cathode-supported fuel cells show an order of the catalytic activity toward hydrogen oxidation - CeO2-delta < Ce0.95Ni0.05O2-delta < Ce0.9Ni0.1O2-delta. The anode polarization resistances in 97% H-2 - 3% H2O are 0.24, 0.31 and 0.37 Omega.cm(2) for Ce0.9Ni0.1O2-delta, Ce0.95Ni0.05O2-delta and CeO2-delta at 600 degrees C, respectively. Thin (La0.9Sr0.1) (Ga0.8Mg0.2)O3-delta-electrolyte fuel cells with nanostructured SmBa0.5Sr0.5Co2O5+delta cathodes and Ce0.9Ni0.1O2-delta anodes yield the highest power densities among the investigated series of anodes, e.g., 820 mW.cm(-2) in 97% H-2 - 3% H2O and 598 mW.cm(-2) in 68% CH3OH - 32% N-2. XPS analyses of reduced nanorods indicate that the highest catalytic activities of Ce0.9Ni0.1O2-delta toward fuel oxidation reactions should be correlated to the presence of highly active Ni nanoparticles and increased surface active oxygen, as confirmed by substantially facilitated extraction of the lattice oxygen on the surface by H-2 in temperature-programmed reduction (TPR) measurements. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

Tailoring the surface chemistry of oxides is effective in adjusting their catalytic behavior. In this study, nickel-doped cerium oxide nanorods were synthesized and evaluated as anode catalysts for solid oxide fuel cells. The results show that the incorporation of nickel significantly enhances the catalytic activity, which is attributed to the presence of nanoparticles and increased surface active oxygen.