DOI: 10.1002/cssc.200800188 Ethanol Oxidation on Electrocatalysts Obtained by Spontaneous Deposition of Palladium onto Nickel-Zinc Materials Valentina Bambagioni, [a] Claudio Bianchini,* [a] Jonathan Filippi, [a] Werner Oberhauser, [a] Andrea Marchionni, [a] Francesco Vizza,* [a] Rinaldo Psaro, [b] Laura Sordelli, [b] Maria Luisa Foresti, [c] and Massimo Innocenti [c] Introduction Primary alcohols with a molecular weight higher than that of methanol are arousing major interest as fuels in direct alcohol fuel cells (DAFC) for various reasons, including their low toxici- ty, high boiling point, high specific energy and, most impor- tantly, the capacity of some of them to be renewable. [1–4] In- cluded in this group is ethanol, which can be produced on a massive scale from biomass feedstocks originating from agri- culture (first-generation bioethanol), forestry and urban resi- dues (second-generation bioethanol). Also, ethanol has a spe- cific energy (6 kWh kg 1 ) comparable to that of gasoline (10– 11 kWh kg 1 ). Despite the high cost, platinum is still the most commonly used metal in manufacturing anode catalysts for fuel-cell elec- trodes. [5] However, apart from methanol for which there exists platinum-based catalysts capable of producing power densities of several tens of mW cm 2 , the higher alcohols such as etha- nol are difficult to oxidize on platinum or platinum alloyed with either noble or non-noble metals. [1–4] In particular, no known anode catalyst based on platinum, even at high metal loadings, has demonstrated the capacity to produce accepta- ble power densities in a direct ethanol fuel cell (DEFC). The best performances so far reported were obtained in active cells at temperatures above 90 8C with binary Pt-Sn and Pt-Ru anode catalysts in conjunction with platinum-based cathodes and Nafion proton-exchange membranes. [1–4] However, the power densities never exceed 60–70 mW cm 2 and the overall efficiency suffers the consequences of the partial oxidation of ethanol to mixtures of acetaldehyde, acetic acid and CO 2 . [1–4] It has been established that a major contribution to the over- ACHTUNGTRENNUNGpotentials of Pt-based anodes in DEFCs is provided by the poi- soning of catalysts by CO, which is an intermediate of ethanol oxidation. [1, 2, 6] For all of these reasons, notable efforts are being carried out in the design of new catalytic structures for DEFC anodes that either do not contain platinum or contain tiny amounts of this metal and, most of all, are able to oxidize ethanol with fast ki- netics, tolerable deactivation with time and high substrate con- centration. Palladium has recently aroused notable interest in electroca- talysis as it is more abundant in nature, hence less expensive than platinum and has the capacity to promote the oxidation of several alcohols, including ethanol, in alkaline media. [2–4] Cur- rent synthetic methods for the preparation of Pd-based elec- trocatalysts for anodes of DAFCs are manifold. [7] Electroless procedures generally involve the adsorption of a palladium [a] Dr. V. Bambagioni, Dr. C. Bianchini, Dr. J. Filippi, Dr. W. Oberhauser, Dr. A. Marchionni, Dr. F. Vizza Istituto di Chimica dei Composti Organometallici (ICCOM-CNR) via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy) Fax: (+ 39) 0555225203 E-mail : claudio.bianchini@iccom.cnr.it [b] Dr. R. Psaro, Dr. L. Sordelli Istituto di Scienze e Tecnologie Molecolari (ISTM-CNR) via C. Golgi 19, 20133 Milano (Italy) [c] Dr. M. L. Foresti, M. Innocenti Dipartimento di Chimica, Università degli Studi di Firenze via della Lastruccia 3, 50019 Sesto Fiorentino (Italy) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.200800188. Ni-Zn and Ni-Zn-P alloys supported on Vulcan XC-72 are effective materials for the spontaneous deposition of palladium through redox transmetalation with Pd IV salts. The materials obtained, Pd- (Ni-Zn)/C and Pd-(Ni-Zn-P)/C, have been characterized by a varie- ty of techniques. The analytical and spectroscopic data show that the surface of Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C contain very small, highly dispersed, and highly crystalline palladium clusters as well as single palladium sites, likely stabilized by interaction with oxygen atoms from Ni O moieties. As a reference material, a nanostructured Pd/C material was prepared by reduction of an aqueous solution of PdCl 2 /HCl with ethylene glycol in the pres- ence of Vulcan XC-72. In Pd/C, the Pd particles are larger, less dis- persed, and much less crystalline. Glassy carbon electrodes coated with the Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C materials, con- taining very low Pd loadings (22–25 mgcm 2 ), were studied for the oxidation of ethanol in alkaline media in half cells and pro- vided excellent results in terms of both specific current (as high as 3600 A g(Pd) 1 at room temperature) and onset potential (as low as 0.6 V vs Ag/AgCl/KCl sat ). ChemSusChem 2009, 2, 99 – 112  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 99