Nanoporous bimetallic Pt–Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid

Abstract

We present a facile route to fabricate novel nanoporous bimetallic Pt–Au alloy nanocomposites by dealloying a rapidly solidified Al₇₅Pt₁₅Au₁₀ precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al₇₅Pt₁₅Au₁₀ precursor is composed of a single-phase Al₂(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt₆₀Au₄₀ nanocomposites (np-Pt₆₀Au₄₀ NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt₆₀Au₄₀ NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt₆₀Au₄₀ NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt₆₀Au₄₀ NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acid fuel cells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance.