Hierarchical Macro-mesoporous Pt Deposits on Gold Microwires for Efficient Methanol Oxidation Matthias Heim, a Chularat Wattanakit, a, c StØphane Reculusa, a, b Chompunuch Warakulwit, c Jumras Limtrakul, c Serge Ravaine, b Alexander Kuhn* a a UniversitØ de Bordeaux 1, CNRS, ISM, ENSCBP, 16 Avenue Pey Berland, 33607 Pessac, France b CNRS, Univ. Bordeaux, CRPP, UPR 8641, 33600 Pessac, France c Department of Chemistry and NANOTEC Center for Nanoscale Materials Design for Green Nanotechnology, Kasetsart University, Bangkok 10900, Thailand *e-mail: kuhn@enscbp.fr Received: September 7, 2011 Accepted: September 16, 2012 Published online: November 5, 2012 Abstract Hierarchically ordered macro-mesoporous Pt films have been synthesized on gold microwires by filling the void space of a colloidal crystal template with mesoporous Pt through electrodepositing the metal in the presence of self- assembled surfactant molecules, followed by a dissolution of the template. The network of interconnected macro- and mesopores in the homogeneous films was characterized using microscopy (SEM, TEM) and electrochemical techniques. The active surface areas of the porous wires increased by more than three orders of magnitude com- pared to nonporous samples. These high surface-to-volume ratios resulted in a high electrocatalytic activity for methanol oxidation. Keywords: Hierarchical structures, Macropores, Mesopores, Electrocatalysis DOI: 10.1002/elan.201200490 1 Introduction In recent years, the elaboration of electrodes with or- dered hierarchical porosity has become an important issue owing to their great potential in various fields of ap- plications including catalysis [1], sensors [2] and conver- sion [3] or storage [4] of energy. Many applications re- quire electrode structures which possess large pores in order to minimize diffusion constraints and smaller pores to efficiently increase the active surface area of the elec- trode. A general pathway to create well-organized porous films on electrode surfaces consists in using template as- sisted electrochemical deposition [5, 6]. By taking advant- age of the structure directing properties of colloidal and lyotropic liquid crystal (LLC) templates, macro- and mes- oporous electrodes have been obtained from a wide range of different materials, respectively [7,8]. Even though several routes for the synthesis of bi- and trimodal carbon and metal oxides exist [3,9–12], only very few re- ports so far have dealt with the fabrication of hierarchical porous metal deposits [2,13–16]. A possibility to reach this goal consists in designing multimodal colloidal tem- plates by chemically bonding spheres of different size to- gether [16]. Deposition of platinum on gold nanoparti- cles, which previously had been infiltrated into the void space of a colloidal crystal, represents another strategy [13]. Furthermore, a double template process has been proposed involving the infiltration of a colloidal template with block copolymers [15] or a LLC template [14]. How- ever, typical concentrations of surfactant molecules in LLCs of more than 40 weight % [17] result in highly vis- cous solutions, preventing them from being uniformly in- troduced into a very confined space like the one inside a colloidal template. This obstacle was overcome by per- forming a heating step [2] or by addition of solvent [14] aiming at reducing the viscosity of the LLC solution prior to the infiltration process. An easier, more straightfor- ward way to meet the defined objective would be to use plating solutions with much lower concentrations of sur- factant. It has been shown that by controlling the poten- tial applied to an electrode a desired configuration of sur- factant phases can be induced at the electrode surface [18–20]. Based on these findings, mesoporous films of metals [21], oxides [22,23] and conducting polymers [24] could be synthesized from solutions with surfactant con- centrations below the critical micelle concentration (cmc), corresponding to 0.1 weight % for sodium dodecyl sulfate (SDS), by taking advantage of potential-controlled assembly of surfactant molecules at the solid-liquid inter- face. In this contribution we present a method for the elaboration of macro-mesoporous Pt films on gold micro- wires by combining colloidal crystal and interfacial sur- factant templating. Gold microwires of different diame- 888  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2013, 25, No. 4, 888 – 894 Full Paper