Changchun Zhao

Fabrication and characterization of nanoporous gold composites through chemical dealloying of two phase Al–Au alloys

We present a facile route to fabricate nanoporous gold composites (NPGCs) through chemical dealloying of two phase Al–Au alloys comprising Al2Au and AlAu intermetallic compounds under free corrosion conditions. The microstructures of the NPGCs were characterized using X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and transmission electron microscopy. The dealloying of Al2Au and AlAu separately proceeds, and results in the formation of the NPGCs. The microstructures of the NPGCs are composed of intracellular and intercellular areas which exhibit two kinds of nanoporous structures with different length scales of ligaments/channels. The nanoporous structure of the intracellular areas forms due to the dealloying of Al2Au and that of the intercellular area forms owing to the dealloying of AlAu. Moreover, the proportion of the intercellular areas in the NPGCs increases with increasing Au content in the starting Al–Au alloys. In addition, the length scale of ligaments/channels in the NPGCs can be adjusted by simply changing the dealloying solution. The NPGCs show abnormal coarsening behaviors when subjected to annealing at different temperatures. In comparison to nanoporous gold (NPG) with a homogeneous structure, the NPGCs exhibit higher Youngs modulus and yield strength. We can tailor the microstructures, properties and applications of these NPGCs through changing the composition of the starting Al–Au alloys, changing the dealloying solution, and adopting proper post treatment including annealing at high temperatures and acid treatment at room temperature.

Formation, control and functionalization of nanoporous silver through changing dealloying media and elemental doping

In this paper, the influence of alloy composition, dealloying solution and elemental doping on the dealloying process of rapidly solidified Mg–Ag based alloys and the formation of nanoporous silver (NPS) has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM). The results show that NPS and nanoporous silver-palladium (NPS–Pd) alloys can be fabricated by dealloying the Mg–Ag based alloys in acid media under free corrosion conditions. The NPS and NPS–Pd exhibit an open, three-dimensional bicontinuous interpenetrating ligament-channel structure. Furthermore, alloy composition and phase constitution of the Mg–Ag precursors have a significant influence on the ligament/channel size and the formation of cracks in NPS. The length scales of ligaments/channels in NPS can be tuned by simply changing the dealloying solution. Crack-free NPS with good mechanical integrity and small ligament/channel sizes can be obtained by dealloying the Mg–Ag alloys in suitable acid solutions. Moreover, the addition of Pd into Mg–Ag has a significant influence on the dealloying process and results in the formation of ultrafine bimodal NPS–Pd with ligaments/channels of ∼5 nm. The NPS–Pd alloy shows excellent hydrogen sensing properties with stable sensitivity, fast response and low detection limit. Our present findings provide implications for control and functionalization of nanoporous metals or alloys by alloy design, selection of dealloying media and elemental doping.

Ultrafine nanoporous Cu–Pd alloys with superior catalytic activities towards electro-oxidation of methanol and ethanol in alkaline media

In this work, the dealloying of ternary Mg–Cu–Pd alloys and formation of nanoporous Cu–Pd alloys have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy dispersive X-ray (EDX) analysis and electrochemical measurements. The results show that the Pd addition has a significant influence on the phase constitution and dealloying process of the rapidly solidified Mg–Cu–Pd alloys. Ultrafine nanoporous Cu–Pd alloy nanostructures with ligaments/channels of less than 10 nm can be obtained in the as-dealloyed samples. The dealloying mechanism and formation of ultrafine nanoporous structures have been rationalized by electrochemical activity measurements and surface diffusion of Cu/Pd adatoms. These ultrafine nanoporous Cu–Pd alloys exhibit high specific surface areas and superior electrocatalytic performance towards electro-oxidation of methanol and ethanol in alkaline media. The present findings provide a facile dealloying route to fabricate nanoporous Cu–Pd alloy electrocatalysts for applications in direct alcohol fuel cells.

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

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.

An ultrafine nanoporous bimetallic Ag–Pd alloy with superior catalytic activity

An ultrafine nanoporous Ag80Pd20 alloy can be fabricated by chemical dealloying of a rapidly solidified Mg60Ag32Pd8 alloy. The addition of the third element Pd into Mg–Ag realizes the design and functionalization of a nanoporous bimetallic structure, which exhibits superior catalytic activity towards electro-oxidation of ethanol.

Fabrication and characterization of magnetic nanoporous Cu/(Fe,Cu)3O4 composites with excellent electrical conductivity by one-step dealloying

In the present study, magnetic nanoporous Cu(NPC)/(Fe,Cu)3O4 composites with tunable magnetism and excellent conductivity were fabricated by a facile one-step dealloying process. Three ternary Al–Cu–Fe alloys with different compositions were chosen as the precursors to carry out the dealloying process in a 20 wt% NaOH solution under free corrosion conditions. The microstructure of these NPC/(Fe,Cu)3O4 composites have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) with nanobeam-EDX (NB-EDX). These NPC/(Fe,Cu)3O4 composites are composed of a NPC matrix with ligament/channel sizes of 20–40 nm and octahedral (Fe,Cu)3O4 embedded particles of 600–800 nm. The formation of these composites has been discussed based upon the surface diffusion of Cu adatoms and oxidation of Fe/Cu adatoms during dealloying. The N2 absorption/desorption results show that the NPC/(Fe,Cu)3O4 composites have a high surface area of up to 25.24 m2 g−1. The maximum values of the magnetic parameters of these NPC/(Fe,Cu)3O4 composites can reach 27.3 emu g−1, 7.7 emu g−1 and 218.5 Oe for the saturation magnetization, remanence and coercivity, respectively. The magnetic properties and the ratio of NPC : (Fe,Cu)3O4 in the NPC/(Fe,Cu)3O4 composites can be tuned by simply changing the Cu/Fe ratio in the Al–Cu–Fe precursor alloys, while keeping their excellent electrical conductivity. These functional composites will find potential applications in sensors, information storage, medical diagnostics, and so forth.

On the vacancy-controlled dealloying of rapidly solidified Mg–Ag alloys

The dealloying of rapidly solidified Mg–Ag alloys with 50–65 at% Mg was performed in HCl solution. The precursor alloys are composed of a single MgAg phase with different vacancy content which exhibits dominant influence on the dealloying process. A vacancy-controlled dealloying mechanism is proposed based on a layer-by-layer model.