Published: February 28, 2011 r2011 American Chemical Society 4456 dx.doi.org/10.1021/jp110011w | J. Phys. Chem. C 2011, 115, 4456–4465 ARTICLE pubs.acs.org/JPCC Length-Scale Modulated and Electrocatalytic Activity Enhanced Nanoporous Gold by Doping Xiaoguang Wang, † Jan Frenzel, ‡ Weimin Wang, † Hong Ji, † Zhen Qi, † Zhonghua Zhang,* ,† and Gunther Eggeler ‡ † Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (MOE), School of Materials Science and Engineering, Shandong University, Jingshi Road 17923, Jinan 250061, People's Republic of China ‡ Institut f€ ur Werkstoffe, Ruhr Universit € at Bochum, Bochum 44780, Germany b S Supporting Information 1. INTRODUCTION Porous materials have recently been attracting considerable attention because of a wide range of applications in catalysis, sensors, heat exchangers, supercapacitors, and so on. 1-4 Among the varieties of porous candidates, nanoporous gold (np-Au) is of special interest due to its unique mechanical, physical, and chemical properties associated with a three-dimensional bicontin- uous interpenetrating ligament-channel structure with a length scale in nanometers. 5-7 With the progress of research toward np- Au, it has been experimentally proved that the size of ligaments/ channels has a significant influence on the associated properties of np-Au. 8 However, the commonly as-obtained np-Au exhibits a characteristic length scale of ligaments/channels located in several tens of nanometers, especially under free corrosion conditions (for example, the ligaments/channels of the np-Au dealloyed from the Au 32 Ag 68 alloy in nitric acid are in the scope of 20- 40 nm when performing at room temperature.). 5,9 It is known that the coarser structure of np-Au is generally obtained through heating treatment and can be modulated to several hundreds of nanometers. 8 However, it is difficult to obtain the ultrafine np-Au with a length scale of ligaments/channels less than 10 nm at room temperature because of fast diffusion of gold atoms along alloy/ electrolyte interfaces. 10 At present, some research groups have reported that the np- Au with an ultrafine microstructure, especially with ligaments/ channels less than 10 nm, reveals lots of peculiar physical, chemical, and mechanical properties, such as strong surface- enhanced Raman spectroscopy, improved effective Young’s modulus, excellent catalytic activity, etc. 8,11,12 Thus, more and more attention has been paid to explore suitable strategies to design ideal np-Au with ultrafine ligaments/channels. Among them, low-temperature and anodic-potential-modulated dealloy- ing techniques are usually applied to fabricate this ultrafine np-Au with ligaments/channels below 10 nm. Qian and Chen 13 have found that the average nanopore can be reduced to ∼7 nm when performing dealloying of Ag-Au alloys at -20 °C for 4 h, and even to a smaller value (∼5 or ∼3 nm) within a shorter dealloying time (1 h or 10 min). In general, the dealloying manipulated at a rigorous low temperature (down to minus tens of degrees centigrade) is complicated and expensive. On the one hand, the dealloying time should be accurately controlled to avoid coarsening as soon as possible. On the other hand, the rather slow reaction kinetics at such a low temperature will unavoidably result in a long reaction time for full dealloying, especially for ribbon-like and bulk precursors. Obviously, the low-temperature method is merely suitable for ultrathin film Received: October 19, 2010 Revised: February 4, 2011 ABSTRACT: In the present paper, we have investigated the dealloying of Pt- and/or Pd-doped Al 2 Au intermetallic compounds and the formation of ultrafine nanoporous Au (np-Au) alloys through a chemical dealloying strategy. The microstructural char- acterization confirms that these doping atoms enter into crystal lattices of the precursors and then transmit into the as-obtained np- Au, both existing in the form of solid solutions. When dealloying in the 20 wt % NaOH solution is performed, a certain amount of Pt and/or Pd addition shows a superior refining effect and the ligament/channel sizes of the as-doped np-Au can be facilely modulated below 10 nm. When dealloying in the 5 wt % HCl solution is performed, however, the anticoarsening capacity of Pt doping is more remarkable compared with that of Pd doping. In addition, the amount of doping also has an important influence on the ligament resistance to coarsening. Apart from causing the refinement of ligaments/channels, the introduction of Pt and/or Pd into np-Au has generated novel bi- or trimetallic functionalized nanoporous alloys. These as-doped np-Au alloys with an appropriate amount of Pt and/or Pd exhibit excellent electrocatalytic activities toward methanol and formic acid oxidation and will find promising applications in the catalysis-related areas.