Electrochemical dealloying of Al2(Au,X) (X = Pt, Pd, PtPd, Ni, Co and NiCo) alloys in NaCl aqueous solution

Abstract

The electrochemical dealloying of rapidly solidified Al2(Au,X) (X = Pt, Pd, PtPd, Ni, Co and NiCo) precursors in a 1.0 M NaCl aqueous solution has been systematically investigated using electrochemical measurements including open-circuit measurement, potentiodynamic polarization and potentiostatic polarization, and microstructural analysis. The results show that the kind of alloying element(s) has a significant influence on the open-circuit and corrosion potentials of the rapidly solidified Al2(Au,X) precursors. The bulk dealloying of the Al2(Au,X) precursors is affected by the kind of alloying element(s) and also sensitive to the applied potential (or overpotential). The addition of Ni or/and Co easily leads to passivation on the surface of precursors during potentiostatic dealloying. The potentiostatic dealloying of Al2(Au,Pt), Al2(Au,Pd) and Al2(Au,Pt,Pd) results in the formation of ultrafine nanoporous AuPt, AuPd and AuPtPd alloys, owing to the pinning effect of Pt or/and Pd on surface diffusion of Au adatoms. In comparison, the potentiostatic dealloying of Al2(Au,Ni), Al2(Au,Co) and Al2(Au,Ni,Co) leads to the formation of nanoporous Au with a ligament/channel size of ~40 nm due to the simultaneous dissolution of Al and Ni/Co. Moreover, the addition of Pt, Pd or PtPd not only inhibits surface diffusion of Au adatoms (lower diffusivities), but also improves the activation energy for the diffusion process during potentiostatic dealloying. Based upon the present results, nanoporous metals or alloys can be greenly fabricated through electrochemical dealloying in NaCl solutions.