Fabrication of bi-modal nanoporous bimetallic Pt–Au alloy with excellent electrocatalytic performance towards formic acid oxidation

Abstract

In the present work, a green and simple strategy has been proposed to fabricate novel bi-modal nanoporous bimetallic Pt–Au alloy by electrochemical dealloying of a ternary Al₇₅Pt₁₅Au₁₀ precursor in a neutral sodium chloride solution. The Al₇₅Pt₁₅Au₁₀ precursor 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 (∼3.5 nm) 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 −0.4 V 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 at 0.6 V 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. Our present findings provide implications for green synthesis of novel multi-functional nanoporous alloys through the electrochemical dealloying strategy in benign neutral salt solutions under mild conditions.