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

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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 Ni 2+ -doped ceria (Ce 1-x Ni x O 2-δ , 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 Ni 2+ 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°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 - CeO 2-δ < Ce 0·95 Ni 0·05 O 2-δ < Ce 0·9 Ni 0·1 O 2-δ . The anode polarization resistances in 97% H 2 – 3% H 2 O are 0.24, 0.31 and 0.37 Ω⋅cm 2 for Ce 0·9 Ni 0·1 O 2-δ , Ce 0·95 Ni 0·05 O 2-δ and CeO 2-δ at 600°C, respectively. Thin (La 0·9 Sr 0.1 ) (Ga 0.8 Mg 0.2 )O 3-δ -electrolyte fuel cells with nanostructured SmBa 0.5 Sr 0·5 Co 2 O 5+δ cathodes and Ce 0·9 Ni 0·1 O 2-δ anodes yield the highest power densities among the investigated series of anodes, e.g. , 820 mW⋅cm −2 in 97% H 2 – 3% H 2 O and 598 mW⋅cm −2 in 68% CH 3 OH - 32% N 2 . XPS analyses of reduced nanorods indicate that the highest catalytic activities of Ce 0·9 Ni 0·1 O 2-δ 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. • Nanorods of Ni 2+ -doped ceria are synthesized as the anode catalysts for SOFCs. • Maximum power densities of 820⋅mW cm −2 were achieved in H 2 at 600°C. • Maximum power densities of 598⋅mW cm −2 were achieved in CH 3 OH at 600°C. • Exsolution of nano-scale Ni particles were observed for Ni 2+ -doped ceria anodes. • Doping Ni 2+ into ceria facilitated surface reduction at low temperatures.