Electrochemically Grown Mesoporous Gold Film as High Surface Area Material for Electro-Oxidation of Alcohol in Alkaline Medium D. H. Nagaraju and V. Lakshminarayanan* Raman Research Institute, C.V.Raman AVenue, Bangalore 560080, India ReceiVed: April 29, 2009; ReVised Manuscript ReceiVed: July 2, 2009 We show here that, by using a simple template free electrodeposition process, it is possible to obtain a dense mesoporous gold film on a metal surface possessing good adhesion, large surface area, and mechanical integrity. The measured electrochemically active true surface area of the film prepared by this method is the highest reported to date for a mesoporous gold surface. The real surface area also increases with increasing time of deposition, showing its potential for scalability. The mesoporous surface was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and cyclic voltammetry (CV). The surface characterization studies confirm the formation of porous film constituted of Au nanoparticles. We find, from the CV studies, that the mesoporous gold surface prepared using the method described here shows excellent catalytic activity for alcohol electro-oxidation in an alkaline medium. 1. Introduction The mesoporous metal thin films on solid supports find several technological applications as materials for catalysis, fuel cells, solar cells, microelectronics, supercapacitors, sensors, and medical diagnostics. 1-4 However, the realization of high surface area mesoporous metal coatings on conductive surfaces poses several challenges which are not trivial. One of the early reports of the formation of a high surface area mesoporous coating is by electrochemical deposition in a lyotropic liquid crystalline phase as a template to produce ordered porous films of platinum possessing high specific surface area, well-defined long-range porosity, and good mechanical and electrochemical stability. 1 The method involves electrodeposition of the required metal through the channels provided by the template in the liquid crystal electrolyte to access the conductive substrate. This is a general synthetic scheme for forming metal films containing a lattice of periodic channels with nanometer dimensions. Ordered porous mesoscale structures of Pt were synthesized by Warren et al. from ligand stabilized Pt nanoparticles loaded in self- assembled block copolymers acting as templates. 3 The frequently used method of preparing 2D and 3D nanostructures of gold is by the process of dealloying where an alloy of Au is treated in a suitable medium to preferentially etch away the alloying metal such as Ag, Al, and Hg, producing a mesoporous structure of gold. 5-8 This method is quite versatile and has generated renewed interest in mesoporous films by expanding their potential applications. We present in this work a simple and effective alternative method of preparing a mesoporous thin film of gold comprised of nanoparticles on a gold substrate by utilizing the unique affinity of the sulfhydryl group to gold 9 and its inhibitory role in limiting the growth of nanoparticles. We have earlier demonstrated an electrochemical method of synthesizing monolayer protected clusters (MPCs) of alkanethi- ols. 10 In this method, gold dissolves anodically in a 1:1 ethanol-water mixture containing 1% by weight of NaBH 4 , 10 mM decanethiol, and 1 M KCl. The dissolved gold ions form a chloroaurate complex in the solution, which is subsequently reduced by NaBH 4 in the electrolyte to produce thiol stabilized gold nanoparticles of about 1-3 nm in size. This is a simple one-step in situ method of preparation of MPCs in the solution, which can then be extracted to a toluene medium and purified. We also demonstrated that the thiol stabilized gold nanoparticles could be produced in the solution even in the absence of NaBH 4 , since, in that event, ethanol can act as the reducing agent. In the present work, we extend the latter method and show that the nanoparticles are formed on the cathode surface as a mesoporous coating, which can find application as an electro- catalyst for alcohol oxidation reactions in alkaline media. 2. Experimental Section 2.1. Chemicals. All of the chemical reagents used in this study were analytical grade (AR) reagents. 11-Mercapto- undecanoic acid (Aldrich), potassium chloride, methanol (Quali- gen), and ethanol (Merck) were used as received. Millipore Milli-Q water having a resistivity of 18 MΩ cm was used to prepare all of the aqueous solutions. 2.2. Surface Characterization. Scanning electron micros- copy (SEM) characterization was carried out using a JEOL JSM- 840A model instrument with an energy dispersive X-ray (EDAX) attachment. Atomic force microscopy (AFM) studies were conducted using a Pico plus (molecular imaging) instru- ment in ac mode (tapping mode) at a frequency of 175 kHz with a cantilever of n + -silicon of type PPP-NCL-50 from nanosensors, USA. The images shown here were corrected for plane tilt using scanning probe image processor (SPIP) software (Image Metrology, Denmark). Surface X-ray diffraction (XRD) measurements of surfaces coated with Au NPs were carried out using an Ultima X-ray diffractometer using Cu KR radiation with a wavelength of 1.540 Å in grazing angle mode. The 2θ values were varied from 10 to 90°. 2.3. Electrochemical Instrumentation. The electrolysis was carried out using an EG&G potentiostat (model 263 A) interfaced to a computer through a GPIB card (National Instruments). This was used to control the current in a chronopotentiometry mode during the electrodeposition in a two- electrode configuration. During the cyclic voltammetry (CV) studies, the potentiostat was used in a normal three-electrode * Corresponding author. E-mail: narayan@rri.res.in. J. Phys. Chem. C 2009, 113, 14922–14926 14922 10.1021/jp903949t CCC: $40.75  2009 American Chemical Society Published on Web 07/28/2009