In this work, the impact of structure and composition on the dealloying of bulk and nanoscale alloys Cu x Au(1–x) have been discussed. In comparison with the dealloying of AgAu alloys, the CuAu system exhibits dealloying curves with more features associated generally with multistage dealloying. It has been shown for the first time that three stages exist during dealloying process of bulk Cu x Au(1–x) (x = 0.7 and 0.8) alloys. The dealloying critical potential, E c, has been associated with the starting point of stage II in which the anodic current slowly increases. Analysis of data from this work along with results of others suggests a monotonic potential dependence of E c upon the composition of bulk Cu x Au(1–x) alloys in the range of x from 0.70 to 0.95. The dealloying behavior of Cu0.75Au0.25 (Cu3Au) intermetallic (length ∼19 nm, width ∼10 nm) and random alloy (length ∼23 nm, width ∼9 nm) nanorods have also been discussed. Very close values of E c have been determined for both types of nanorods with the random alloy dealloying at slightly more negative potentials (c.a. 15–20 mV) than the intermetallic. In addition, both Cu3Au nanorods feature close to 200 mV lower E c than bulk alloys with identical composition. Formic acid oxidation tests reveal that the catalysts generated by platinization of as-synthesized and dealloyed nanorods exhibit very good activity with peak current densities in the range of 3.5 to 5.5 mA.cm–2. Both catalysts withstand testing of more than 1500 cycles. Overall, the results of this study demonstrate unique aspects of Cu x Au(1–x) dealloying and ascertain the feasibility of nanosized frameworks (dealloyed structures or nanoparticles) as catalyst supports in fuel cell applications.

Abstract:The fabrication of a nanoporous gold (NPG)-based catalyst on a glassy carbon (GC) support results normally in large isolated and poorly adhering clusters that suffer considerable material loss upon durability testing. This work exploits thermochemical oxidation of GC, which, coupled with the utilization of some recent progress in fabricating continuous NPG layers using a Pd seed layer, aims to enhance the adhesion to the GC surface. Thermochemical oxidation causes interconnected pores within the GC structure to open and substantially improves the wettability of the GC surface, which are both beneficial toward the improvement of the overall quality of the NPG deposit. It is demonstrated that thermochemical oxidation neither affects the efficiency of the Au 0.3 Ag 0.7 alloy (NPG precursor) deposition nor hinders the achievement of continuity in the course of the NPG fabrication process. Furthermore, adhesion tests performed by a rotating disk electrode setup on deposits supported on thermochemically-oxidized and untreated GCs ascertain the enhanced adhesion on the thermochemically-oxidized samples. The best adhesion results are obtained on a continuous NPG layer fabricated on thermochemically-oxidized GC electrodes seeded with a dense network of Pd clusters.

Electrodeposited CuxAu(1-x) thin films with different compositions have been found to undergo selective dissolution (de-alloying) in three specific potential ranges unlike their bulk counterparts known to de-alloy at composition dependent critical potentials. The general potential trend associated with coexistence of different thermodynamically stable alloy phases suggests increasing de-alloying rate in positive direction with the decreasing Cu content in the alloy. Following de-alloying, the resulting nanoporous Au (NPG) thin films exhibit significant surface area (SA) development, manifested by about threefold increase in comparison with de-alloyed AgxAu(1-x) precursor counterparts. SEM characterization have seconded the SA results by revealing a finer structure of the NPG films which feature pores and ligaments of less than 10 nm. Formic acid oxidation tests suggest that the platinization of accordingly synthesized NPG thin films leads to the synthesis of catalysts exhibiting initial mass activities of 3-5 A.mg-1 (combined Pt-Au catalyst) and withstanding more than 2500 potential cycles.

Thin continuous films of platinized nanoporous Au (Pt-NPG) catalyst have been synthesized by all-electrochemical routines including successive Ag x Au (1-x) deposition and de-alloying. However, when deposited on inexpensive substrates like glassy carbon (GC), the alloy precursor grows in isolated clusters. This constitutes a challenge addressed in the present work by using a Pd seeding process to promote continuity in NPG films on GC. The approach relies on electroless seeding of an ultra high density Pd cluster network that facilitates the coalescence at very low thickness of the deposited alloy precursor. The seeding has been performed in both naturally aerated and de-oxygenated PdCl 2 solutions on Sn 2+ sensitized GC electrodes. Also, the alloy deposition process has been studied in the presence and absence of O 2 and with different supporting electrolytes. The O 2 content of both seeding and deposition solutions has been identified as a key factor in controlling the densification of the NPG-based catalyst. Electrochemical and SEM characterizations have been used to assess the outcome of the densification process. The alloy compositional homogeneity has been examined by de-alloying polarization curves. The surface area evolution has been studied by Pb UPD. Optimum conditions for achieving continuity of the deposit have been elucidated and further discussed.

Glass fiber reinforced epoxy composites with various carbon nanotube loadings are fabricated and studied by Guang‐Lin Zhao and co‐workers in their article, number http://doi.wiley.com/10.1002/adem.201900780. The composites show high microwave absorption and low mass density with much enhanced tensile strength, which provides a multifunctional potential for various applications.