The microstructural refinement and performance improvement of a nanoporous Ag/CeO catalyst for NaBH oxidation.

In this paper, Cu and Ce were added to melt-spun Al-Ag precursor alloys to refine the microstructures of nanoporous Ag and Ag/CeO composite catalysts for NaBH oxidation. After the precursor alloys were dealloyed in 20% NaOH, calcined in air and corroded again in 50% NaOH, AgAl in the precursor alloys was completely removed, and refined nanoporous Ag could be obtained; from this process, the finest microstructures were exhibited by AlAgCu. When more than 0.3% Ce was added to the AlAgCu ribbons, a refined nanoporous Ag material that consisted of CeO nanorods interspersed between Ag ligaments was obtained. Electrochemical measurements indicated that the catalytic properties were clearly increased due to the Cu addition to the Al-Ag alloy. After Ce was added to the AlAgCu ribbons, the catalytic properties of the resulting material were further improved. In regard to melt-spun AlAgCuCe, the obtained nanoporous Ag/CeO presented the best properties, and its current density was 2.5 times that of AlAgCu, 3.1 times that of AlAgCu and 2.3 times that of Ag/Ce from the AlAgCe precursor alloy without Cu. It was believed that the core-shell structure composed of Ag and Cu-rich phases formed during dealloying could limit the diffusion of Ag and prevent the coarsening of Ag ligaments. Thus, the refined microstructures could provide a large specific surface or additional active sites for the catalytic reaction. Strong interactions resulted from the many interfaces between the Ag ligaments and interspersed CeO nanorods, and the more effective utilization of Ag was due to the decomposition of AgAl; this result was the key reason for the clear improvement in catalytic performance.