The Preparation And Electrochemical Application Of Nanoporous Au/Alloys

A green and simple strategy has been proposed to fabricate novel bi-modal nanoporous bimetallic Pt-Au alloy by electrochemical dealloying of a ternary Al75Pt15Au10precursor in a neutral sodium chloride solution. The Al75Pt15Au10precursor is composed of a single Al2(Pt,Au) phase with lattice vacancies inside. The bi-modal nanoporous Pt-Au alloy exhibits an island-channel structure and the islands show an ultrafine three-dimensional bicontinuous interpenetrating ligament-channel (～3.5nm) characteristic. The dealloying mechanism of the precursor and the formation of the nanoporous structure have been addressed using electrochemical measurements (potentiodynamic and potentiostatic polarization) and microstructural analysis (scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis). The dealloying at the low potential of-0.4V vs. Ag/AgCl is associated with the partial dissolution of Al and the disappearance of the vacancies, leading to the formation of the stoichiometric Al2(Pt,Au). The subsequent dealloying at0.6V vs. Ag/AgCl is related to the complete dissolution of Al and surface diffusion of Pt/Au, resulting in the formation of the ultrafine nanoporous structure. Besides, the bi-modal nanoporous Pt-Au alloy shows superior catalytic activity towards the electro-oxidation of formic acid in the acid media in comparison to the commercial JM-Pt/C catalyst.The electrochemical dealloying of doped Al2Au(M) alloys in aqueous sodium chloride solutions with different doped elements have been systematically investigated using electrochemical measurements including open circuit measurement, potentiodynamic polarization (tafel) and potentiostatic polarization, and microstructural analysis. On the whole, both the open circuit potentials and the corrosion potentials of the doped Al2Au(M) alloys are markedly influenced by the addition of M elements. The addition of Pt and Pd can increase the Eocp and Ecor values while the addition of Ni and Co hardly alters the Ecop and Ecor values of Al2Au. During the dealloying process, the inert instinct of Pt and Pd results in the decrease of reaction rate while the addition of Ni and Co easily leads to passivation on the surface of alloys during the electrochemical dealloying process. Pt and Pd atoms with a low surface diffusivity have a dramatical pinning effect on mobile Au atoms, thus leading to the formation of the ultrafine nanostructure with ligaments/channels of as small as5～10nm. However, it is hard to retain the Ni and Co during the electrochemical dealloying process. Besides, ligaments/channels size is of～40nm, equal to the NPG fabricated by pure Al2Au. Due to the difference between the diffusion coefficients of Pt and Pd, these two doped elements have different pitting effects on the Auad surface diffusion process. The addition of Ni and Co has little effect on the Auad surface diffusion. This leads to the order of Ds values as follows:Al2Au(Pt)<Al2Au(Pt, Pd)<Al2Au(Pd)<Al2Au(Ni). The addition of doped elements has a similar influence on the activation energy (Ea) values.