Study On The Dealloying Of Al-X-Pd (X=Cu, Ag) Alloys And The Formation Of Nanoporous Alloys

In this paper, we chose rapidly solidified Al-X-Pd (X= Cu, Ag) ribbons as the starting alloys. We have investigated the dealloying mechanisms of the Al-X-Pd alloys through analyzing the chemical/electrochemical process of these alloys as well as the microstructure of the as-dealloyed products. It has been found that the phase constituents of the rapidly solidified Al-Cu-Pd alloys markedly change, but those of the Al-Ag-Pd alloys do not alter with increasing Pd addition into the starting alloys. The addition of Pd has a significant influence upon the dealloying processes of the rapidly solidified Al-Cu-Pd and Al-Ag-Pd alloys and the formation of nanoporous alloys. The Al-Cu-Pd system with different Pd contents can be fully dealloyed in the HCl solution under free corrosion conditions forming nanoporous alloy structures, accompanied by the partial dissolution of Cu. The Al-30Ag-5Pd alloy can be dealloyed in the HCl solution forming nanoporous Ag-Pd alloy, but the Al-25Ag-10Pd alloy can be partially dealloyed in the same solution. Moreover, the characteristic length scale of nanoporous alloys through dealloying of the Al-Cu-Pd and Al-Ag-Pd alloys can be greatly refined, due to suppression on the diffusion of Cu and Ag adatoms along the alloy/solution interface by the Pd adatoms with slower diffusivities. The open-circuit and Tafel measurements have demonstrated that the electrochemical activities of the rapidly solidified Al-Cu-Pd alloys decrease with increasing Pd content in the starting alloys. Ultrafine nanoporous Cu-Pd alloys can be fabricated by electrochemical dealloying of the Al-Cu-Pd alloys in the 1M HC1 solution. Nanoporous Cu-Pd alloys exhibit excellent catalytic activities towards electro-oxidation of methanol, formic acid and especially ethanol, which show wide application prospects in direct alcohol and direct formic acid fuel cells.