Impact of the Synthetic Route on the De-Alloying of Electrodeposited Cu3au Alloys

Abstract

The development of highly active, durable, and cost-effective catalysts is essential in today’s fuel cell industry. Virtually all such catalysts include high priced Pt.1 A preferred synthetic route aimed at reducing total catalyst cost involves the use of an inert support coated by a small amount of Pt-based catalyst. A good candidate for the support is nanoporous Au (NPG).1-3 This conductive material has an open, 3D porous framework with surface areas that even in ultra thin NPG layer configuration are tens to hundreds of times larger than the area of planar Au. Once deposited, on a commonly C-based support, the NPG can be further functionalized with Pt by surface-limited redox replacement (SLRR) to form Pt-NPG, and then applied as the catalyst in the formic acid oxidation reaction.4 In our previous work, we established an all-electrochemical synthetic method for a NPG-based catalyst.4 This fabrication procedure entails Au(1−x)Agx alloy electrodeposition followed by selective dissolution of Ag (de-alloying) ultimately generating the desired NPG structure with a thickness of less than 20nm. To further study nanoporous Au, in this report we switch our focus to a Cu3Au precursor alloy synthesized/electrodeposited through various routes. After the synthetic step we selectively dissolve the Cu to fabricate the NPG with interest in its structural and morphological characteristics. More specifically, the Cu3Au alloys of interest are generated by conventional bulk deposition, Underpotential co-deposition (UPCD)5 and surfactant mediated electrochemical deposition6. The de-alloying process of accordingly generated ultra-thin films is compared to the parting behavior of chemically synthesized Cu3Au nanorods (intermetallic and random alloy).7-9 The de-alloying curves from each of the nanomaterial studied in this work exhibit quite unique behavior owing to size and structural differences. Overall, the de-alloying curves for the Cu3Au thin films illustrate multiple peaks that indirectly suggest phase coexistence in the precursor alloy. Along with that, the Cu3Au nanoparticles de-alloying is presented for comparison. The NPG resulting from the de-alloying process has been studied for surface area development by Pb Underpotential deposition (Pb UPD). X-ray Diffraction (XRD) is used to study the potential presence of different phases. Scanning electron microscope (SEM) and Transmission Electron Microscopy (TEM) images display the morphology before and after de-alloying. Finally, basic tests of the catalytic properties of various Pt-coated de-alloyed structures during formic acid oxidation are presented and discussed as well. Reference: L. Bromberg, J. Xia, M. Fayette, and N. Dimitrov; J. Electrochem.Soc, 2014, 161(7), D3001-D3010.M.Collinson; ISRN Analytical Chemistry, 2013. 2013: p. 21M. Kamundi, L. Bromberg and N. Dimitrov; J. Phys. Chem. C 2012, 116, 14123−14133D.McCurry, M.Kamundi and N. Dimitrov; ACS Appl. Mater. Interfaces 2011, 3, 4459–4468Defu Liang and Giovanni Zangari; Langmuir 2014, 30, 2566−2570S. R. Brankovic, N. Dimitrov and K. Sieradzki; Electrochem. Solid-State Lett. 1999, 2, (9), 443-445S.Chen,S. Jenkins, J.Taoand J. Chen; J. Phys. Chem. C 2013, 117, 8924−8932Bracey, C. L.; Ellis, P. R.; Hutchings, G. J; Chem. Soc. Rev. 2009, 38, 2231−2243.Jana, N. R.; Gearheart, L.; Murphy, C. J; Adv. Mater. 2001,13, 1389−1393.